Fragile-X mutation and Klinefelter syndrome: a reappraisal.

To date the concurrent presence of the fragile-X and the Klinefelter syndromes in the same individual has been found at least 8 times either in the course of screening for the fra(X) condition in mentally retarded males or among the relatives of fra(X) propositi. Given the high frequency of both events in the general population and the heterogeneous approaches with which the above cases were ascertained, it has not been possible to determine unequivocally so far whether the finding is purely coincidental or the expression of some underlying biological relationship. To evaluate the issue, we have screened a large population of institutionalized mentally retarded males for microorchidism, and submitted to a full karyotype analysis and fra(X) testing the patients that were found to have marked bilateral microorchidism. Thus, in a total of 32 microorchidism patients identified among 1115 mentally retarded males, we found 6 to have a 47,XXY chromosome complement in all (or in most) of their cells, with one of them having also the fra(X) marker in 9% of the metaphases examined. In addition, another bearer of the fra(X) marker (but only in 4% of his metaphases) was found among 26 47,XXY mentally normal males ascertained throughout routine cytogenetic analysis of males with microorchidism referred to our genetic counseling unit during the last 10 years. In our laboratory the fra(X) marker has never been observed with such a frequency in a total of several hundred normal XY males and XX females studied as control cases in the course of previously reported family and population studies.(ABSTRACT TRUNCATED AT 250 WORDS)