Genetic Disorders - X-linked Genetic Disorders

X-Linked genetic disorders (XLGDs) can be either dominant or recessive. Dominant XLGDs affect females and males. Dominant XLGD's include: Albright's hereditary osteodystrophy (seizures, mental retardation, stunted growth), Goltz's syndrome (mental retardation), cylindromatosis (deafness and upper body tumors), oralfacial-digital syndrome (no teeth, cleft tongue, some mental retardation), and incontinentia pigmenti (abnormal swirled skin pigmentation).

Recessive XLGDs are passed to sons through their mothers, who are carriers. Often, a carrier mother will have an affected male relative. Major XLGDs include: severe combined immune deficiency syndrome (SCID), color blindness, hemophilia, Duchenne's muscular dystrophy (DMD), some spinal ataxias, and Lesch-Nyhan syndrome. Roughly one third of these XLGDs result from a spontaneous mutation. Of these disorders, color blindness is the most benign.

Hemophilia is a more serious XLGD caused by failure of one of the clotting proteins, which serves to prevent an injured person from bleeding to death. Hemophilia A is the most severe form of this disease, and is characterized by extreme bleeding. It primarily affects males, although a few females can develop symptoms. This disease has been associated with royalty, as England's queen Victoria was a carrier and her descendants became rulers in several European countries.