Section 504. Individuals with disabilities may not be excluded from participating in programs and services receiving federal funds. It also prohibits job discrimination against people with disabilities in any program receiving federal financial assistance. Students not eligible for an Individualized Education Program (IEP) may be eligible for a 504 plan.

Single-nucleotide polymorphism. DNA sequence variation occurring when a single nucleotide adenine (A), thymine (T), cytosine (C), or guanine (G]) in the genome (or other shared sequence) differs between members of a species or paired chromosomes in an individual.

Smooth muscles. Muscles that are part of or surround internal organs, as along the gastrointestinal tract.

Social Security Disability Insurance (SSDI). A federal insurance program that provides cash assistance for individuals who have worked under Social Security long enough to have “insured status” and who are disabled. SSDI also includes disability benefits and other kinds of benefits for some family members of individuals who are insured and who have died, retired, or become disabled. Most individuals who qualify for SSDI also qualify for Medicare after they have been entitled to benefits for two years. For more information, visit: www.socialsecurity.gov/disability.

Somatic. Physical.

Somatic mosaicism. In DM1, the presence of different numbers of CTG repeats (the abnormality) found in different organs and systems within the same person; in DM2, the presence of different numbers of CCTG repeats found in different organs and systems within the same person.

Sonogram. An image created by ultrasound obtained by a computerized instrument; it can reveal internal parts of the body, such as thyroid gland or fetus in utero.

Southern blot. Method used in molecular biology for detection of a specific DNA sequence in DNA samples.

Steinert’s disease. The first name given to myotonic dystrophy when it was identified as a disease by Dr. Hans Steinert of Germany in 1909.

Strabismus. Inability of one eye to attain binocular vision with the other because of imbalance of the muscles of the eyeball--called also heterotropia, squint.

Sudden heart block. A condition of the heart in which the passage of an electrical impulse is arrested, wholly or in part, temporarily or permanently.

Supplemental Security Income (SSI). Supplemental Security Income (SSI) is a cash benefit for people who are elderly, blind, and/or disabled and who have very limited income and assets. Unlike Social Security Disability Insurance (SSDI), individuals do not need to have any work history to qualify for SSI assistance. SSI payments do not come from Social Security taxes and there is no insured status requirement as in SSDI.