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XXX syndrome—this is trisomy XXX and other multiple X-chromosomal abnormalities. Many of these girls are phenotypically normal but may have mild mental retardation and menstrual abnormalities.
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DiGeorge syndrome—this is also known as 22q11.2 deletion syndrome and is a syndrome caused by the deletion of a small segment of chromosome 22. There is failure of the development of the third and fourth pharyngeal pouches so there is agenesis of the parathyroid glands and thymus. There is T-cell deficiency, hypocalcemia, congenital heart problems, certain facial features, frequent infections, developmental delay, learning problems and cleft palate.
AUTOSOMAL DOMINANT DISORDERS Autosomal dominant disorders have the characteristic of being associated with an autosomal gene and not a sex gene. It is dominant, meaning there is no carrier state as the individual who has the disorder will likely have the disease unless there is incomplete penetrance. The likelihood of passing on this type of gene disorder is 50 percent to both male and female offspring. These are the major autosomal dominant disorders: •
Autosomal dominant polycystic kidney disease—this has an onset in adult life and can lead to chronic renal failure and death. There are multiple cysts in the kidneys, leading to enlarged kidneys. There may also be liver cysts. People with this condition are born with one mutated copy of the PKD1 or PKD2 gene in each cell. About 90 percent of these cases are inherited with the rest being sporadic mutations.
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Ehlers-Danlos syndrome—this represents a wide-ranging group of inherited, usually autosomal dominant disorders, involving different defects in collagen synthesis. This connective tissue disease involves joint laxity, extreme elasticity of the skin, and poor wound healing. The most common cause of death is a dissecting aortic aneurysm.
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Familial hypercholesterolemia—this is an autosomal dominant defect in the LDLreceptor. It leads to accelerated atherosclerosis in the person who is heterozygous 7
