An abnormal large human chromosome identified as an end‐to‐end fusion of two X's by combined results of the new banding techniques and microdensitometry

An abnormal large chromosome was described by Gouw et al. (1964) in the karyotype (46 X‐X?) of a patient presenting a Turner‐like syndrome. The structure of this abnormal chromosome, re‐studied with the new banding techniques (Quinacrine mustard fluorescence completed with micro‐densitometric recordings, modified Giemsa and centromeric stainings) appears to be the result of a fusion of two X chromosomes, short arms to short arms. This chromosome is not dicentric but C‐heterochromatin has been demonstrated on its long arms, at the probable centromeric region of the second X involved in the fusion. These findings, their relation to the clinical features and their possible mechanisms of formation, are discussed.