Consanguinity is noted more often among the parents of individuals with rare recessive disorders. A consanguineous relationship noted in the parents of a patient with an unidentified genetic disorder suggests the possibility of an autosomal recessive single gene disorder. An X-linked disorder is one in which the altered gene is located on the X chromosome. The hallmark of X-linked inheritance is that there is no male to male transmission, since males pass on Y chromosomes to their sons. Unaffected males cannot transmit the disorder because they do not carry the abnormal X-linked gene.
Affected males have clinically normal offspring.
Their sons receive a Y chromosome and are free of the trait. Their daughters receive an X chromosome and are normal, but obligate carriers. Sons who inherit the gene will be affected and daughters will be carriers like their mothers. Female carriers may be mildly symptomatic due to unequal inactivation of the X chromosomes. Although unlikely, a female can express an X-linked disorder if her father is affected and her mother is a carrier.