Occurrence of Rett syndrome in boys

The neurologic disorder Rett syndrome was originally described exclusively in girls. We present two boys with clinical features of Rett syndrome. Othe r than head circumference deceleration, no longer considered mandatory, pat ient I meets all of the criteria. Using fluorescent in situ hybridization a nalysis, 97.6% of cells were found to be karyotypically normal (46,XY). No mutation was detected on screening of the coding region of the MECP2 gene. The second patient also has classic features of Rett syndrome. However, cyt ogenetic analysis of peripheral blood revealed a karyotype 47,XXY[23]/46,XY [7] confirming mosaicism for Klinefelter's syndrome. A T158M missense mutat ion in the methylcytosine-binding domain of the MECP2 gene was identified. A diagnostic bias against the clinical identification of Rett syndrome in b oys may exist. This presentation of the male phenotype could be more common than it would appear, although boys with MECP2 mutations might also manife st in other ways. Rett syndrome remains a clinical diagnosis that should no t be dismissed in boys, and thorough evaluation including karyotype and mut ation testing is warranted.