[Genetics and epidemiology of XXXX ].

@entity5 @entity1 @entity74 @entity995
Recent studies of genetic epidemiology of @entity995 are reviewed, and major conclusions drawn are as follows: @entity995 occurs in heritable or nonheritable form. The primary @entity74 in the heritable form is a point mutation or deletion at a locus on 13 q 14. For the genesis of a @entity5 in either form, the loss or inactivation of both alleles at this locus is a prerequisite, although additional events may be needed for its development. Information about environmental risk factors for the occurrence of heritable or nonheritable @entity995 is still meager. Although viral etiology for nonheritable @entity5 cannot be excluded, an extensive epidemiologic study revealed no seasonal variation in the births of 675 @entity1 with sporadic unilateral cases, a great majority of which may be regarded as due to somatic mutation. Moreover, there was no paternal age effect at all on the occurrence of 225 sporadic bilateral cases. Paternal exposure to ionizing radiation or chemical mutagens, which should have an accumulated effect with advancing age, does not seem to play a major role in the production of germinal mutation at the Rb locus. Family studies show that host resistance genes at other loci can modify the process of @entity5 development when the primary @entity74 is already present in all the target cells. Unaffected gene carriers may be regarded as inherently resistant to @entity5 formation, whereas @entity1 who present early onset of @entity5 are the most susceptible. In certain families, however, non-expression in the carriers may be due to chromosomal rearrangement in a balanced state.
