Two cases of familial paracentric inversion in man associated with sex chromosome anomaly. 47,XXY,inv(5)(q21q32) and 45,X,inv(7)(q11.3q22.3).

A paracentric inversion of chromosome 5 was detected after RHG banding in a subject affected by Klinefelter's syndrome. The inversion was also observed in the patient's mother, and was confirmed by QFQ- and RBA-banding techniques. A second paracentric inversion affecting chromsome 7 was detected in a woman with Turner's syndrome. The same structural anomaly was found in her father and her half-brother. The possible relationship between sex chromosome nondisjunction and paracentric inversion is discussed. Furthermore, the inversion of chromosome 7 reproduces exactly the chromosome 7 of the gorilla, which is presumed to be ancestral to the human 7. This therefore appears to be the first reported case of reverse chromosomal mutation.