Is down syndrome genetic disorder
Down syndrome - Symptoms and causes
Overview
The genetic basis of Down syndrome
The genetic basis of Down syndrome
There are 23 pairs of chromosomes, for a total of 46. Half the chromosomes come from the egg (the mother) and half come from the sperm (the father). This XY chromosome pair includes the X chromosome from the egg and the Y chromosome from the sperm. In Down syndrome, there is an additional copy of chromosome 21, resulting in three copies instead of the normal two copies.
Down syndrome is a genetic disorder caused when abnormal cell division results in an extra full or partial copy of chromosome 21. This extra genetic material causes the developmental changes and physical features of Down syndrome.
Down syndrome varies in severity among individuals, causing lifelong intellectual disability and developmental delays. It's the most common genetic chromosomal disorder and cause of learning disabilities in children. It also commonly causes other medical abnormalities, including heart and gastrointestinal disorders.
Better understanding of Down syndrome and early interventions can greatly increase the quality of life for children and adults with this disorder and help them live fulfilling lives.
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Symptoms
Each person with Down syndrome is an individual — intellectual and developmental problems may be mild, moderate or severe. Some people are healthy while others have significant health problems such as serious heart defects.
Children and adults with Down syndrome have distinct facial features. Though not all people with Down syndrome have the same features, some of the more common features include:
- Flattened face
- Small head
- Short neck
- Protruding tongue
- Upward slanting eye lids (palpebral fissures)
- Unusually shaped or small ears
- Poor muscle tone
- Broad, short hands with a single crease in the palm
- Relatively short fingers and small hands and feet
- Excessive flexibility
- Tiny white spots on the colored part (iris) of the eye called Brushfield's spots
- Short height
Infants with Down syndrome may be average size, but typically they grow slowly and remain shorter than other children the same age.
Intellectual disabilities
Most children with Down syndrome have mild to moderate cognitive impairment. Language is delayed, and both short and long-term memory is affected.
When to see a doctor
Children with Down syndrome usually are diagnosed before or at birth. However, if you have any questions regarding your pregnancy or your child's growth and development, talk with your doctor.
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Causes
Human cells normally contain 23 pairs of chromosomes. One chromosome in each pair comes from your father, the other from your mother.
Down syndrome results when abnormal cell division involving chromosome 21 occurs. These cell division abnormalities result in an extra partial or full chromosome 21. This extra genetic material is responsible for the characteristic features and developmental problems of Down syndrome. Any one of three genetic variations can cause Down syndrome:
- Trisomy 21.
About 95 percent of the time, Down syndrome is caused by trisomy 21 — the person has three copies of chromosome 21, instead of the usual two copies, in all cells. This is caused by abnormal cell division during the development of the sperm cell or the egg cell. - Mosaic Down syndrome. In this rare form of Down syndrome, a person has only some cells with an extra copy of chromosome 21. This mosaic of normal and abnormal cells is caused by abnormal cell division after fertilization.
- Translocation Down syndrome. Down syndrome can also occur when a portion of chromosome 21 becomes attached (translocated) onto another chromosome, before or at conception. These children have the usual two copies of chromosome 21, but they also have additional genetic material from chromosome 21 attached to another chromosome.
There are no known behavioral or environmental factors that cause Down syndrome.
Is it inherited?
Most of the time, Down syndrome isn't inherited.
It's caused by a mistake in cell division during early development of the fetus.
Translocation Down syndrome can be passed from parent to child. However, only about 3 to 4 percent of children with Down syndrome have translocation and only some of them inherited it from one of their parents.
When balanced translocations are inherited, the mother or father has some rearranged genetic material from chromosome 21 on another chromosome, but no extra genetic material. This means he or she has no signs or symptoms of Down syndrome, but can pass an unbalanced translocation on to children, causing Down syndrome in the children.
Risk factors
Some parents have a greater risk of having a baby with Down syndrome. Risk factors include:
- Advancing maternal age. A woman's chances of giving birth to a child with Down syndrome increase with age because older eggs have a greater risk of improper chromosome division. A woman's risk of conceiving a child with Down syndrome increases after 35 years of age.
However, most children with Down syndrome are born to women under age 35 because younger women have far more babies. - Being carriers of the genetic translocation for Down syndrome. Both men and women can pass the genetic translocation for Down syndrome on to their children.
- Having had one child with Down syndrome. Parents who have one child with Down syndrome and parents who have a translocation themselves are at an increased risk of having another child with Down syndrome. A genetic counselor can help parents assess the risk of having a second child with Down syndrome.
Complications
People with Down syndrome can have a variety of complications, some of which become more prominent as they get older. These complications can include:
- Heart defects. About half the children with Down syndrome are born with some type of congenital heart defect. These heart problems can be life-threatening and may require surgery in early infancy.
- Gastrointestinal (GI) defects. GI abnormalities occur in some children with Down syndrome and may include abnormalities of the intestines, esophagus, trachea and anus. The risk of developing digestive problems, such as GI blockage, heartburn (gastroesophageal reflux) or celiac disease, may be increased.
- Immune disorders. Because of abnormalities in their immune systems, people with Down syndrome are at increased risk of developing autoimmune disorders, some forms of cancer, and infectious diseases, such as pneumonia.
- Sleep apnea. Because of soft tissue and skeletal changes that lead to the obstruction of their airways, children and adults with Down syndrome are at greater risk of obstructive sleep apnea.
- Obesity. People with Down syndrome have a greater tendency to be obese compared with the general population.
- Spinal problems. Some people with Down syndrome may have a misalignment of the top two vertebrae in the neck (atlantoaxial instability).
This condition puts them at risk of serious injury to the spinal cord from overextension of the neck. - Leukemia. Young children with Down syndrome have an increased risk of leukemia.
- Dementia. People with Down syndrome have a greatly increased risk of dementia — signs and symptoms may begin around age 50. Having Down syndrome also increases the risk of developing Alzheimer's disease.
- Other problems. Down syndrome may also be associated with other health conditions, including endocrine problems, dental problems, seizures, ear infections, and hearing and vision problems.
For people with Down syndrome, getting routine medical care and treating issues when needed can help with maintaining a healthy lifestyle.
Life expectancy
Life spans have increased dramatically for people with Down syndrome. Today, someone with Down syndrome can expect to live more than 60 years, depending on the severity of health problems.
Prevention
There's no way to prevent Down syndrome. If you're at high risk of having a child with Down syndrome or you already have one child with Down syndrome, you may want to consult a genetic counselor before becoming pregnant.
A genetic counselor can help you understand your chances of having a child with Down syndrome. He or she can also explain the prenatal tests that are available and help explain the pros and cons of testing.
By Mayo Clinic Staff
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Down syndrome: MedlinePlus Genetics
Description
Down syndrome is a chromosomal condition that is associated with intellectual disability, a characteristic facial appearance, and weak muscle tone (hypotonia) in infancy. All affected individuals experience cognitive delays, but the intellectual disability is usually mild to moderate.
People with Down syndrome often have a characteristic facial appearance that includes a flattened appearance to the face, outside corners of the eyes that point upward (upslanting palpebral fissures), small ears, a short neck, and a tongue that tends to stick out of the mouth.
Affected individuals may have a variety of birth defects. Many people with Down syndrome have small hands and feet and a single crease across the palms of the hands. About half of all affected children are born with a heart defect. Digestive abnormalities, such as a blockage of the intestine, are less common.
Individuals with Down syndrome have an increased risk of developing several medical conditions. These include gastroesophageal reflux, which is a backflow of acidic stomach contents into the esophagus, and celiac disease, which is an intolerance of a wheat protein called gluten. About 15 percent of people with Down syndrome have an underactive thyroid gland (hypothyroidism). The thyroid gland is a butterfly-shaped organ in the lower neck that produces hormones. Individuals with Down syndrome also have an increased risk of hearing and vision problems. Additionally, a small percentage of children with Down syndrome develop cancer of blood-forming cells (leukemia).
Delayed development and behavioral problems are often reported in children with Down syndrome.
Affected individuals can have growth problems and their speech and language develop later and more slowly than in children without Down syndrome. Additionally, speech may be difficult to understand in individuals with Down syndrome. Behavioral issues can include attention problems, obsessive/compulsive behavior, and stubbornness or tantrums. A small percentage of people with Down syndrome are also diagnosed with developmental conditions called autism spectrum disorders, which affect communication and social interaction.
People with Down syndrome often experience a gradual decline in thinking ability (cognition) as they age, usually starting around age 50. Down syndrome is also associated with an increased risk of developing Alzheimer disease, a brain disorder that results in a gradual loss of memory, judgment, and ability to function. Approximately half of adults with Down syndrome develop Alzheimer disease. Although Alzheimer disease is usually a disorder that occurs in older adults, people with Down syndrome commonly develop this condition earlier, in their fifties or sixties.
Frequency
Down syndrome occurs in about 1 in 700 newborns. About 5,300 babies with Down syndrome are born in the United States each year, and approximately 200,000 people in this country have the condition. Although women of any age can have a child with Down syndrome, the chance of having a child with this condition increases as a woman gets older.
Causes
Most cases of Down syndrome result from trisomy 21, which means each cell in the body has three copies of chromosome 21 instead of the usual two copies.
Less commonly, Down syndrome occurs when part of chromosome 21 becomes attached (translocated) to another chromosome during the formation of reproductive cells (eggs and sperm) in a parent or very early in fetal development. Affected people have two normal copies of chromosome 21 plus extra material from chromosome 21 attached to another chromosome, resulting in three copies of genetic material from chromosome 21. Affected individuals with this genetic change are said to have translocation Down syndrome.
A very small percentage of people with Down syndrome have an extra copy of chromosome 21 in only some of the body's cells. In these people, the condition is called mosaic Down syndrome.
Researchers believe that having extra copies of genes on chromosome 21 disrupts the course of normal development, causing the characteristic features of Down syndrome and the increased risk of health problems associated with this condition.
Inheritance
Most cases of Down syndrome are not inherited. When the condition is caused by trisomy 21, the chromosomal abnormality occurs as a random event during the formation of reproductive cells in a parent. The abnormality usually occurs in egg cells, but it occasionally occurs in sperm cells. An error in cell division called nondisjunction results in a reproductive cell with an abnormal number of chromosomes. For example, an egg or sperm cell may gain an extra copy of chromosome 21. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra chromosome 21 in each of the body's cells.
People with translocation Down syndrome can inherit the condition from an unaffected parent. The parent carries a rearrangement of genetic material between chromosome 21 and another chromosome. This rearrangement is called a balanced translocation. No genetic material is gained or lost in a balanced translocation, so these chromosomal changes usually do not cause any health problems. However, as this translocation is passed to the next generation, it can become unbalanced. People who inherit an unbalanced translocation involving chromosome 21 may have extra genetic material from chromosome 21, which causes Down syndrome.
Like trisomy 21, mosaic Down syndrome is not inherited. It occurs as a random event during cell division early in fetal development. As a result, some of the body's cells have the usual two copies of chromosome 21, and other cells have three copies of this chromosome.
Other Names for This Condition
- 47,XX,+21
- 47,XY,+21
- Down's syndrome
- Trisomy 21
- Trisomy G
Additional Information & Resources
Genetic Testing Information
- Genetic Testing Registry: Complete trisomy 21 syndrome
Genetic and Rare Diseases Information Center
- Down syndrome
Patient Support and Advocacy Resources
- Disease InfoSearch
- National Organization for Rare Disorders (NORD)
Research Studies from ClinicalTrials.
gov- ClinicalTrials.gov
Catalog of Genes and Diseases from OMIM
- DOWN SYNDROME
Scientific Articles on PubMed
- PubMed
References
- Antonarakis SE, Lyle R, Dermitzakis ET, Reymond A, Deutsch S. Chromosome 21 and down syndrome: from genomics to pathophysiology. Nat Rev Genet. 2004 Oct;5(10):725-38. doi: 10.1038/nrg1448. Citation on PubMed
- Capone G, Goyal P, Ares W, Lannigan E. Neurobehavioral disorders in children, adolescents, and young adults with Down syndrome. Am J Med Genet C Semin Med Genet. 2006 Aug 15;142C(3):158-72. doi: 10.1002/ajmg.c.30097. Citation on PubMed
- Carter JC, Capone GT, Gray RM, Cox CS, Kaufmann WE. Autistic-spectrum disorders in Down syndrome: further delineation and distinction from other behavioral abnormalities. Am J Med Genet B Neuropsychiatr Genet. 2007 Jan 5;144B(1):87-94. doi: 10.1002/ajmg.b.30407.
Citation on PubMed - Chapman RS, Hesketh LJ. Behavioral phenotype of individuals with Down syndrome. Ment Retard Dev Disabil Res Rev. 2000;6(2):84-95. doi: 10.1002/1098-2779(2000)6:23.0.CO;2-P. Citation on PubMed
- Cohen WI. Current dilemmas in Down syndrome clinical care: celiac disease, thyroid disorders, and atlanto-axial instability. Am J Med Genet C Semin Med Genet. 2006 Aug 15;142C(3):141-8. doi: 10.1002/ajmg.c.30102. Citation on PubMed
- de Graaf G, Buckley F, Skotko BG. Estimates of the live births, natural losses, and elective terminations with Down syndrome in the United States. Am J Med Genet A. 2015 Apr;167A(4):756-67. doi: 10.1002/ajmg.a.37001. Citation on PubMed
- de Graaf G, Buckley F, Skotko BG. Estimation of the number of people with Down syndrome in the United States. Genet Med. 2017 Apr;19(4):439-447. doi: 10.1038/gim.2016.127. Epub 2016 Sep 8. Citation on PubMed
- Kumin L.
Speech intelligibility and childhood verbal apraxia in children with Down syndrome. Downs Syndr Res Pract. 2006 Jul;10(1):10-22. doi: 10.3104/reports.301. Citation on PubMed - Lott IT, Head E. Alzheimer disease and Down syndrome: factors in pathogenesis. Neurobiol Aging. 2005 Mar;26(3):383-9. doi: 10.1016/j.neurobiolaging.2004.08.005. Citation on PubMed
- Lubec G, Engidawork E. The brain in Down syndrome (TRISOMY 21). J Neurol. 2002 Oct;249(10):1347-56. doi: 10.1007/s00415-002-0799-9. Citation on PubMed
- Roizen NJ, Patterson D. Down's syndrome. Lancet. 2003 Apr 12;361(9365):1281-9. doi: 10.1016/S0140-6736(03)12987-X. Citation on PubMed
- Shapiro BL. Down syndrome and associated congenital malformations. J Neural Transm Suppl. 2003;(67):207-14. doi: 10.1007/978-3-7091-6721-2_18. Citation on PubMed
- Sherman SL, Allen EG, Bean LH, Freeman SB. Epidemiology of Down syndrome.
Ment Retard Dev Disabil Res Rev. 2007;13(3):221-7. doi: 10.1002/mrdd.20157. Citation on PubMed - Steingass KJ, Chicoine B, McGuire D, Roizen NJ. Developmental disabilities grown up: Down syndrome. J Dev Behav Pediatr. 2011 Sep;32(7):548-58. doi: 10.1097/DBP.0b013e31822182e0. No abstract available. Citation on PubMed
- Zigman WB, Lott IT. Alzheimer's disease in Down syndrome: neurobiology and risk. Ment Retard Dev Disabil Res Rev. 2007;13(3):237-46. doi: 10.1002/mrdd.20163. Citation on PubMed
Down's syndrome
Down's syndrome is a genetic disease that causes mental retardation, delayed physical development, and congenital heart defects. In addition, it is often accompanied by impaired thyroid function, impaired hearing, and vision.
Down's syndrome is the most common disorder caused by chromosome anomalies. As the mother ages, the risk of having a child with Down syndrome increases.
There is no cure for the condition and its severity may vary.
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Treatment depends on the manifestations of the disease. Although it is impossible to get rid of the syndrome itself, working with a defectologist from an early age contributes to the development of the child's mental functions.
Synonyms Russians
Trisomy on the 21st chromosome, trisomy G.
Synonyms English
Down Syndrome, Down Syndromy 21.
Symptoms 9000. there are specific facial features and structural features of the head:
- small head,
- wide face,
- short neck, excess skin on back of neck,
- short and wide nose
- underdeveloped upper jaw,
- light gray spots on the iris up to the 12th month of life,
- epicanthus - a semilunar skin fold in the inner corner of the upper eyelid - the "third eyelid" - and, as a result, a narrow, Mongoloid incision of the eyes, nine0031 small, asymmetrical, low-attached ears,
- large tongue without central groove, often open mouth,
- misaligned teeth.
The following symptoms are also typical for Down syndrome patients:
- low muscle tone,
- disproportionate physique,
- underdevelopment of sexual characteristics,
- wide short palms with one crease instead of two, the thumb is placed low in relation to the other fingers,
- sandal gap between the first and second toes,
- relatively short, overly flexible fingers.
Children with Down syndrome usually develop more slowly than normal. They begin to sit, crawl and walk about twice as late as children with normal development.
Patients also have a moderate degree of mental retardation.
General information about the disease
Down syndrome is a genetic disease caused by an abnormality of the 21st chromosome, which manifests itself in the form of mental retardation, heart defects and developmental disorders. nine0003
It is often accompanied by dysfunction of the thyroid gland, impaired hearing and vision.
There are 23 pairs of chromosomes in the human chromosome set. In this case, one chromosome from the pair comes from the mother, one from the father. There are 46 chromosomes in the body.
The cause of Down's disease is an anomaly of the 21st chromosome, which is characterized by the presence of additional copies of genetic material on the 21st chromosome in the form of a trisomy or translocation. The 21st chromosome affects almost all organ systems and is responsible for the traits and developmental features that are impaired in Down's disease. nine0003
- Trisomy 21 suggests the presence of a copy of this chromosome. That is, instead of two chromosomes, the 21st pair is represented by three. Thus, in all cells of the body there are three chromosomes of the 21st pair instead of two.
Trisomy accounts for 95% of chromosome 21 anomalies. It occurs when there is a violation of cell division during the formation of germ cells (spermatozoa and eggs) of the parents.
Almost always, an extra chromosome is passed on to a child with Down syndrome from the mother. As the age of the mother increases, the risk of having a child with Down syndrome increases. The older the egg, the greater the likelihood of abnormal cell division. nine0003
- The mosaic variant of the syndrome occurs when only some cells of the body have an abnormal copy of the 21st chromosome. The "mosaic" of abnormal and normal cells is due to a violation of cell division after fertilization in the embryo.
- Translocation of the 21st chromosome to other chromosomes (more often to the 15th or 14th). Children have two chromosome 21 pairs and extra material on chromosome 21. At the same time, part of the 21st chromosome moves to another when chromosome division is disturbed during the formation of spermatozoa and eggs of the parents (about 25% of cases of translocation) or at the time of conception (about 75% of cases). nine0032
Down's syndrome is thus caused by a defect in cell division during the development of an egg, sperm or fetus.
Down syndrome is not a hereditary disease, although there is a predisposition to its development. Women with Down syndrome have a 50% chance of having an affected child, and spontaneous miscarriage often occurs. Men with Down syndrome are infertile, except for the mosaic variant of the syndrome.
Carriers of a genetic chromosome translocation will also have an increased chance of having a child with Down syndrome. If the mother is the carrier, a child with Down syndrome is born in 10-30%, if the father is the carrier - in 5%. nine0003
Women who have a child with Down syndrome have a 1% chance of having a second child with Down syndrome.
Children with Down syndrome may experience the following complications.
- Heart defects. Approximately half of children with Down syndrome are born with heart defects that may require surgery in early childhood.
- Leukemia (malignant disease of the hematopoietic system). Children with Down syndrome, especially at an early age, are more likely to develop leukemia than other children.
nine0032 - Infectious diseases. Due to disorders of the body's immune system, children with Down syndrome are more susceptible to infectious diseases.
- Dementia. After the age of 40, Down syndrome patients are at an increased risk of developing dementia.
- Sleep apnea. Children with Down syndrome are prone to sleep apnea, a condition in which ventilation is interrupted for 20 to 30 seconds during sleep. In severe cases, sleep apnea can take up to 60% of a night's sleep. Regular sleep apnea leads to daytime sleepiness, memory impairment, decreased intelligence, performance and constant fatigue. nine0032
- Obesity.
The life expectancy of people with Down syndrome depends on the severity of manifestations and averages 50 years or more.
Who is at risk?
- Women with Down syndrome (men with Down syndrome are usually infertile).
- Mothers after 30 years. With age, the risk of giving birth to a child with Down syndrome increases: by the age of 35 it is 1 in 400, by 45 - 1 in 35.
However, approximately 80% of children with Down syndrome are born to mothers under 35 years old. nine0032 - Fathers over 42.
- Carriers of genetic translocation of chromosomes. If the mother is the carrier, the risk of having a child with Down syndrome is about 10-30%, if the father is about 5%.
- Parents who already have a child with Down syndrome. The risk of having another child with this disease is approximately 1%.
Diagnosis
The diagnosis is made on the basis of a characteristic clinical picture. Newborns are tested for Down syndrome. Pregnant women are also assigned studies aimed at identifying Down syndrome in the fetus. nine0003
Down's syndrome is suspected based on the presence of features of appearance characteristic of this disease. The diagnosis is confirmed by karyotyping - a study of the child's chromosomes for abnormalities.
In addition, the functions that may be impaired in Down's syndrome are investigated - thyroid function, visual, auditory analyzers.
Possible heart defects, leukemia are detected.
- Thyroid stimulating hormone (TSH) is a hormone produced by the pituitary gland, a small gland located in the brain. It regulates the functioning of the thyroid gland. If its function is impaired, its level, as a rule, changes. nine0032
- Thyroxine is a hormone produced by the thyroid gland and affects many types of metabolism in the body. With Down's syndrome, its level can be reduced.
- Bone marrow biopsy. Examination of a bone marrow sample under a microscope reveals leukemia.
Fetal Down syndrome may be suspected by screening and ultrasound findings. All pregnant women are advised to test for alpha-fetaprotein. In addition, the examination of pregnant women involves the following tests. nine0003
First trimester of pregnancy
- Human chorionic gonadotropin (hCG) is a hormone produced by the fetal membrane and is involved in maintaining pregnancy.
- Pregnancy-associated plasma protein A (PAPP A).
Abnormal levels of hCG and PAPP-A may indicate fetal developmental disorders.
Second trimester of pregnancy
- Ultrasound examination - allows you to identify abnormalities in the development of the fetus. nine0031 Alpha-fetoprotein (alpha-FP) - its low level may indicate Down's syndrome.
- Beta subunit of human chorionic gonadotropin (beta hCG). An increase in the concentration of hCG in some cases is associated with a child's illness.
- Estriol free. Low estriol levels are a sign of Down syndrome.
The results of ultrasound, PAPP-A, alpha-FP, hCG and estriol, combined with data on the age and heredity of the mother, allow us to calculate the risk of having a child with Down syndrome. nine0003
These studies are especially important for women who are at risk for having children with this disease.
If the risk is found to be very high, the following tests may be performed.
- Amniocentesis - taking a sample of amniotic fluid and then examining the chromosomes of the fetus.
- Chorionic biopsy - obtaining a tissue sample from the chorion (the outer germinal membrane surrounding the embryo). Allows detection of chromosomal abnormalities.
- Cord blood sampling - allows to detect chromosomal abnormalities. The test is performed if previous studies have been ineffective. nine0032
For women with a predisposition to the disease, genetic counseling is recommended during pregnancy planning.
Treatment
Down syndrome cannot be cured, so therapy is directed at specific manifestations of the disease.
If necessary, surgical operations are performed to treat heart defects, anomalies of the gastrointestinal tract, examination by a neurologist, cardiologist, ophthalmologist, defectologist, speech therapist, pediatrician, etc.
Early treatment will maximize the development of children with Down syndrome and improve their quality of life. Immediately after birth, it is extremely important to develop the motor, cognitive sphere of the child, his mental functions.
There are special preschool and school institutions where a program has been developed for children with an appropriate level of intelligence.
Prevention
Prevention of the birth of children with Down syndrome has not been developed. People who are at risk of having a child with this disease are advised to undergo a genetic test during pregnancy planning. nine0003
Recommended tests
- Human chorionic gonadotropin free beta (free beta hCG)
- Plasma pregnancy-associated protein A (PAPP A)
- Alpha-fetoprotein (alpha-FP)
- Free estriol
- Thyroid Stimulating Hormone (TSH)
- Thyroxine free (T4 free)
- General thyroxine (T4)
Literature
- Dan L. Longo, Dennis L. Kasper, J. Larry Jameson, Anthony S. Fauci, Harrison's principles of internal medicine (18th ed.). New York: McGraw-Hill Medical Publishing Division, 2011.
Down Syndrome - Symptoms, Risks, Early Diagnosis
Down Syndrome is a genetic disorder caused by abnormal cell division that results in an extra full or partial copy of chromosome 21. This extra genetic material causes developmental changes and physical features Down syndrome. nine0003
The manifestations of the syndrome vary in severity from person to person, causing lifelong mental retardation and developmental delay. This is the most common genetic chromosomal disorder and is the cause of limited learning ability in children. It also often causes other medical problems, including heart and gastrointestinal problems.
Unfortunately, a large number of stereotypes and misconceptions about this condition are still widespread in Russia. In addition, not all future parents know what to do in order to identify the risks of this syndrome. nine0003
In this article we will describe the main facts about Down syndrome and talk about the possibilities of modern genetic diagnostics, which allow us to detect this syndrome in time.
Down syndrome is one of the most common chromosomal abnormalities. Most of the manifestations of this condition are associated with trisomy - the presence of an additional complete or partial copy - of chromosome 21. This anomaly accounts for up to 90% of cases of Down syndrome.
Interesting fact
Why does chromosome 21 have exactly this serial number
In 1959, when the first conference on the creation of the International System of Human Cytogenetic Nomenclature (ISCN) was held, scientists decided to number the non-sex chromosomes from 1 to 22 in accordance with their decreasing size. So, the smallest chromosome was numbered 22, and the largest - 1. However, at that time, geneticists did not yet have reliable tools for accurately assessing the size of each chromosome, and later it turned out that the 21st chromosome was still smaller than the 22nd. However, several studies have already been published linking the onset of Down syndrome to trisomy 21.
To avoid confusion, the numbering was not changed. So chromosome 21 retained its number despite being the smallest. nine0003
Source: Thomas Eggermann and Gesa Schwanitz 2011
The cause of trisomy 21 has not yet been clearly identified. It is generally accepted that it is the result of a spontaneous error, which manifests itself in the inability of the 21st chromosome to separate during the development of an egg or sperm.
Source: National Human Genome Research Institute
In addition to the standard trisomy of chromosome 21, Down syndrome can be caused by its various chromosomal rearrangements: Robertsonian translocations, reciprocal translocations, duplications, submicroscopic aberrations. In rare cases of Down syndrome, mosaicism or mutation of chromosome 21 has been identified. The rarest case of Down syndrome is chromosome 21 tetrasomy - the presence of four free chromosomes 21, or two normal chromosomes and, in addition, isochromosome 21. Aberration usually leads to death in early pregnancy.
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Learn more about the genetics of Down syndrome
Our geneticists have extensive experience in advising on congenital genetic diseases, including Down syndrome. You can sign up for a consultation and get answers to all questions about the genetic causes of this disease, as well as assess the risk of its occurrence in your future children. You can sign up by phone 8 (499) 677-52-22 or via chat.
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Down syndrome - symptoms
In addition to the well-known features of the disease, such as mental retardation and learning difficulties, Down syndrome has more than 80 other phenotypic manifestations, including those that affect the central nervous system, heart, gastrointestinal tract, skeleton, and immune system. The phenotypes associated with Down syndrome vary in both frequency and severity, resulting in a wide range of phenotypic combinations.
Cognitive impairment, hypotension, and craniofacial features are universal phenotypes, while cardiac anomalies affect only about half of people with Down syndrome.
Individual phenotypes similar to those seen in Down syndrome have been documented in individuals without trisomy 21, but the overall higher frequency and severity of these phenotypes in individuals with Down syndrome suggests that trisomy plays an important role in initiating or modifying these features. Although it has been suggested that common mechanisms may be involved in the similar phenotypes seen in people with and without trisomy 21, the overall pathophysiology must be proven for each individual phenotype. nine0003
Source: Roper and Reeves, 2006
People with Down syndrome are at increased risk of congenital heart disease, epilepsy, leukemia, thyroid disease, and various mental disorders. Due to various physiological manifestations of the syndrome, such as growth retardation, low muscle tone, flexible ligaments, short arms, atlantoaxial joint instability, and others, their quality of life is markedly reduced. Most often, they cannot have children, or their children inherit the syndrome.
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15 times more often
Leukemia occurs in children with Down syndrome.
Down syndrome - how to assess the risk?
Down syndrome occurs in approximately 1 in 660 newborns. At the same time, the risk of giving birth to a child with this syndrome increases with the age of the mother. In 20-year-old mothers, it is less than 0.1% and increases gradually to 3% in mothers aged 45.
0.5% of newborns
On average, this is exactly the frequency of manifestation of Down syndrome in developed countries. However, it should be noted that this risk increases with the age of the mother. nine0003
The age of the mother remains the only factor by which we can assess the risk of having Down's syndrome before conception. Parents of children with this condition are usually healthy, and no behavioral or environmental factors affect the likelihood of having a child with this syndrome.
Various prenatal tests and comprehensive studies are used to assess the risk of Down's syndrome after conception.
non-invasive prenatal tests remain the safest and most reliable way
- Safe
- Informative
- Fast
- Exactly
Benefits of NIPT
The non-invasive prenatal test requires only the venous blood of a pregnant woman, which contains small fragments of her own genetic material and fragments of the extracellular fetal DNA of the unborn child. With the help of a unique technology, extracellular fetal DNA is isolated, followed by its sequencing by the NGS method. Thanks to this, we can accurately assess the risks of Down syndrome in the fetus. nine0003
The choice of a non-invasive prenatal test depends on many factors. The main things we pay attention to are the history, the gestational age, whether the pregnancy occurred naturally or after IVF, whether donor cells were used in the IVF cycle, the number of fetuses, the presence of a missing twin, what are the results of other tests, and so on.
Want to choose NIPT?
Our geneticist will review the circumstances of your pregnancy and help you select a non-invasive prenatal test to assess your risk of Down syndrome.
