Also known as trisomy 21, a common form of mental retardation caused by a chromosomal abnormality; formerly called mongolism. Two types are recognized, based on the nature of the chromosomal aberration: the translocation type and the non-disjunction type. Physical findings include widely spaced eyes with slanting openings, small head with flattened occiput, lax joints, flabby hands, small ears, and congenital anomalies of the heart.
Also known as trisomy 21, a common form of intellectual disability caused by a chromosomal abnormality formerly called mongolism. Two types are recognized, based on the nature of the chromosomal aberration: the translocation type and the nondisjunction type. Physical findings include widely spaced eyes with slanting openings, small head with flattened occiput, lax joints, flabby hands, small ears, and congenital anomalies of the heart.
A birth defect related to faulty chromosomes. Chromosomal aberrations are of three types: (a) trisomy 21, (b) translocation, or (c) mosaicism.
Down syndrome is a relatively well-known genetic disorder that is strongly associated with mental retardation. It is usually identified at birth and is confirmed by a karyotype showing trisomy of Chromosome 21. Down syndrome usually is caused by an error in cell division called nondisjunction. However, two other types of chromosomal abnormalities, mosaicism and translocation, also are implicated in Down syndrome, although to a much lesser extent. Regardless of the type of Down syndrome that a person may have, all people with Down syndrome have an extra, critical portion of the Chromosome 21 present in all, or some, of their cells.
Down syndrome can result from three genetic errors in cell division. Over 90% of the cases constitute the full form, Trisomy 21. Instead of the normal pair, every cell in the body has three number 21 chromosomes. Mosaic Trisomy 21, present in 2-4% of the cases, results when the extra Chromosome 21 is present in some, but not all, cells. The remaining 2-4% of the Down syndrome cases are caused by a translocation. This occurs when cells, in addition to the normal complement of 46 chromosomes, have material from Chromosome 21 stuck or translocated onto another chromosome. With translocation Trisomy 21, the individual still has features associated with Down syndrome (National Institute of Child Health and Human Development [NICHD], 2000).
A congenital condition resulting from a chromosomal abnormality, usually the existence of three copies (trisomy) of chromosome 21, instead of the normal two; also called Down syndrome, trisomy 21, or congenital acromicria. Down’s syndrome is the most common cause of mental retardation, affecting one in approximately 600 to 650 births. Children with Down’s syndrome characteristically have eyes that slope upward at the outer corners and are partly covered by epi- canthal folds, folds of skin on the inner corners, giving them a supposedly “Asian” appearance (hence, the earlier name, mongolism). They also tend to have small facial features, a large tongue, a skull flattened in the back, and hands with a single horizontal palm crease. Down’s syndrome children are unusually likely to have heart problems, atresia (narrowing) in the intestinal system, ear and hearing problems, leukemia, and atherosclerosis (narrowing of the arteries)—so much so that, until recent medical advances, relatively few reached full adulthood. No treatment is known to alter the course of Down’s syndrome.
Congenital defect, usually caused by the presence of an extra No. 21 chromosome (trisomy) and characterized by mental retardation (the I.Q. averages 50- 60); oblique placement of the eyes; a small head flattened at the back; a large, furrowed tongue; short stature; bowel defects; and heart abnormalities. The syndrome, the most common of the chromosomal abnormalities, is associated with advanced maternal age, especially over age 35 (1 in 80 off-spring of women over 40 will be affected); it can be detected through amniocentesis. Care of a Down’s syndrome child involves both the prevention of physical problems (e.g., respiratory infections, to which these children are especially prone) and long-range programs to promote mental and motor skills. A less common form of the disease, caused by a translocation of a chromosome, is an inherited (genetic) defect, not associated with maternal age.
A genetic defect that causes characteristic (mongoloid) facial features as well as varying degrees of mental retardation and other defects.
A chromosomal abnormality that results in mental retardation and other complications. Down syndrome results from an extra copy of chromosome 21 and is also known as trisomy 21. Pregnant women aged 35 or older have a significantly increased risk of having a baby with Down syndrome.
A form of mental sub-normality due to a chromosome defect (there are three no. 21 chromosomes instead of the usual two). The main physical features are a slightly oblique slant to the eyes, as in Mongolian persons (hence the former name of this condition, mongolism); a round head; flat nasal bridge; fissured tongue; abnormalities of the palms, including single transverse creases and characteristic dermal ridges; small round or knotty ears; and short stature. Many of these features are present at birth, enabling an early diagnosis; the condition can also be diagnosed prenatally, by ‘amniocentesis. The ultimate mental attainment is about that of a five year-old child, i.e. an IQ of 50-60. Rare partial forms of Down’s syndrome occur with a slightly higher IQ.
A genetic disorder in which the affected person usually carries an extra chromosome 47 instead of the usual 46. The extra chromosome occurs in the no. 21 group, hence the disorder is described as trisomy 21. The condition was named after Dr J L H Down, the London doctor who first described it in 1866. The incidence is around one in 600 births. The disorder is characterized by a particular physical appearance and learning difficulties. Most people with the syndrome have eyes that slope up at the outer corners and vertical skin folds that cover the inner corners. The face and features are smaller than normal, while the tongue is larger; the back of the head is flattened and the hands are usually short and broad. Muscles tend to be floppy and they have a tendency to be overweight.
A chromosomal abnormality leads to individuals experiencing varying degrees of learning difficulties and exhibiting characteristic physical features.
Individuals with Down’s syndrome possess an additional chromosome, resulting in a total of 47 chromosomes instead of the typical 46. The condition is often referred to as trisomy 21 since those affected have three copies of chromosome number 21 instead of the usual two. In most instances, the cause is a mistake during meiosis, where a sperm or egg is formed with an extra chromosome 21, as the chromosome pair fails to separate properly into distinct cells. If fertilization involves one of these abnormal sperm or egg cells, the resulting baby will also inherit the extra chromosome. This type of abnormality is more commonly observed when the mother is over the age of 35.
An infrequent cause is a genetic irregularity known as a translocation, where a portion of one parent’s 21st chromosome combines with a different chromosome. Although this doesn’t impact the parent, it significantly increases their likelihood of having children with Down Syndrome.
Individuals with Down’s syndrome commonly exhibit distinct physical characteristics. These can include a petite facial structure, eyes that slope upwards, and extra skin folds at the inner corners of the eyes. A larger than average tongue, a back of the head that appears flat, and short, wide hands marked by a single crease across the palm are also typical features. Their height is generally shorter than the average. It’s common for those with Down’s syndrome to experience learning challenges, which can vary from mild to severe. Despite these difficulties, many are known to possess cheerful and amiable dispositions.
Individuals with Down’s syndrome face an increased risk of certain health issues. One potential complication is a congenital heart defect, prevalent in up to 40% of newborns with this condition. They also may encounter challenges such as intestinal atresia, which is a constriction in the intestines, and innate hearing loss. Children with Down’s syndrome tend to be more prone to acute leukemia compared to their peers. They are particularly vulnerable to ear infections as well. Moreover, adults with Down’s syndrome who are above 40 years of age have a heightened risk of developing Alzheimer’s disease.
In the early stages of pregnancy, certain screening tests such as a nuchal translucency ultrasound, which measures the thickness of the skin at the back of the fetus’ neck, can help identify the likelihood of the baby having Down syndrome. If these screenings indicate a high probability, an amniocentesis may be suggested. This test involves analyzing the chromosomes of fetal cells. In some instances, Down syndrome may not be detected until after the child is born. To confirm the diagnosis, a chromosome analysis is performed using cells from the baby.
While there is no cure for Down syndrome, children with this condition can maximize their abilities through suitable environmental and educational stimulation and support. Many children acquire skills such as reading and writing, and some adults may even be capable of working. However, the majority of individuals with Down syndrome cannot live independently and require continuous care either from their families or within a residential care facility.