Severely affected offspring may be born to minimally affected adults. An autosomal recessive disorder is one which is fully expressed only when a mutation is present in both genes of a pair. It is highly unusual to find other affected individuals in preceding or succeeding generations. The disorder is generally found only in sibs, thus resulting in a horizontal pattern of inheritance. Either sex can be affected, on average in equal numbers.
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.