[Clinical and cytogenetic problems in diagnosis of fragile X syndrome].

The fragile X or Martin-Bell syndrome is the second most common chromosomal cause of mental retardation. It has a prevalence of 1:1000; the clinical and psychopathologic symptoms vary. The difficult diagnosis rests on cytogenetic evidence of the fragile site at Xq 27.3. 18 patients were tested for fragile X syndrome in 4 different laboratories. Of the 32 chromosomal analyses performed 17 were positive and 15 negative. In 11 patients 2 or more analyses were performed in different laboratories for verification. In all 11 cases the findings were discrepant and therefore the initial findings were considered false positive. The clinical and cytogenetic problems are discussed and diagnostic guidelines summarized.