The use of testicular volume as a clinical marker for cytogenetic disorders in mentally retarded males.

The testicular volumes (V) of 817 adult (non-Down's syndrome) institutionalized males were calculated. The mean testicular volume was 19.5 +/- 15.8 ml, comparable to the normal adult male mean of 17-19 ml. However, the number of institutionalized males with V greater than or equal to 25 ml and V less than or equal to 10 ml was increased approximately fourfold over the normal male population. Resident adult males were grouped into three categories based on their testicular volumes: (1) V greater than or equal to 25 ml (macro-orchid); (2) V less than or equal to 15 ml (micro-orchid); and (3) 15 less than V less than 25 ml ('normal'). An equal number of randomly selected males from each category were cytogenetically screened for the fra(X) syndrome as well as for non-fra(X) chromosome abnormalities. The overall frequencies of these disorders were 3.1% and 3.9%, respectively. The fra(X) syndrome was found in a significantly higher percentage of macro-orchid males (10.3%) as compared to males with either micro-orchidism (1.2%) or normal testicular volume (1.2%). There was no significant difference in the distribution of either fra(X) negative non-specific XLMR or non-fra(X) chromosome abnormalities among resident males from these three categories. Testicular volumes greater than or equal to 25 ml, especially those exceeding 40 ml, were thus shown to be useful clinical markers in the diagnosis of the fra(X) syndrome. Reduced testicular volume was not a useful clinical marker in the evaluation of other non-Down's syndrome chromosome abnormalities.