Down’s syndrome is a genetic disorder caused by having three copies of the genes found on chromosome 21, rather than the normal two copies. Normal human cells have 23 paired chromosomes. Individuals with Down ’s syndrome have an extra chromosome 21 in their cells. This extra chromosome can be either a full or partial copy of chromosome 21. While Down’s syndrome is strongly associated with intellectual disability, those afflicted are at increased risk for conditions affecting the gastrointestinal, cardiovascular, endocrine, and special senses systems.
Down ’s syndrome is reported as occurring in approximately 1 out of 1000 births worldwide making it the most common genetic disorder caused by chromosomal abnormality. The incidence of Down’s syndrome correlates directly to increased maternal age, reaching approximately 1 in 10 births for woman of 49 years of age. Although Down’s syndrome is a genetic disorder, it is generally not inherited; rather it is typically the result of improper cell division during development of the egg, sperm, or embryo. There are three genetic variations that cause Down’s syndrome, which are listed below.
Chromosome 21 trisomy is by far the most prevalent type of Down’s syndrome, accounting for 95% of cases. It is caused by an error in cell division called nondisjunction. This causes the reproductive cell of either the mother or father to have an extra copy of chromosome 21. The reproductive cells of mother and father fuse to create a fertilized egg or zygote. Because the original genetic material making up this single cell has an additional copy of chromosome 21, all future cells will also contain this variation.
Mosaic Down’s syndrome is the rarest form of Down’s syndrome accounting for only about 1% of cases. Individuals with this type of Down’s syndrome have a mixture of normal and abnormal cells in their body. This is because with Mosaic Down’s syndrome, nondisjunction occurs after fertilization.
Translocation Down’s syndrome occurs when part of chromosome 21 attaches (translocates) onto another chromosome. Individuals with this type of Down’s syndrome will have two copies of chromosome 21 while also having parts of chromosome 21 attached to the translocated chromosome. This type of Down’s syndrome is sometimes called familial Down’s syndrome because it can be inherited from a parent.
Social Security Medical Listing 10.06 – Non-mosaic Down’s Syndrome
The Social Security Administration ‘s Listing of Impairments gives criteria for non-mosaic Down’s syndrome, and thus is only to be used for the translocation and chromosome 21 trisomy varieties of Down’s syndrome. If you have non-mosaic Down’s syndrome, providing a report of karyotype analysis signed by a physician is proof of disability as defined by Social Security. If you do not have karyotype testing, a physician’s report that you have Down’s syndrome with the distinctive physical features accompanied with evidence that you function at a level consistent with non-mosaic Down’s syndrome will suffice.
If you have mosaic Down’s syndrome that has resulted in an inability to sustain full time work for a year or more you may also qualify for disability benefits. Your representative can help you determine if your condition is severe enough for you to qualify for disability benefits under the Social Security Administration.