Transmission of an unbalanced (Y;1) translocation in Brittany, France.

Unbalanced and balanced Y;autosome translocations are rare structural rearrangements that constitute a heterogeneous group. According to Nielsen and Rasmussen, the frequency of these translocations in the general population is approximately 1 in 2000 (six cases out of 11 148 newborn infants). All these six cases were in an unbalanced form. In the majority of cases, there is a non-reciprocal translocation of the heterochromatic region of the long arm of the Y chromosome to the short arm of an acrocentric chromosome, most frequently a chromosome 15. 3 Most of these translocations are familial and transmitted down several generations through both sexes. No increased incidence of infertility or spontaneous abortions has been reported in these families. Invariably, subjects with this type of translocation have a normal male or female phenotype. The majority of carriers with an unbalanced Y;acrocentric chromosome translocation are detected incidentally through newborn cytogenetic surveys or during the familial investigation of an infant with congenital anomalies. Another group is composed of balanced reciprocal Y;autosome translocations. This group consists of translocations between the Y chromosome and any autosome excluding the short arm of the acrocentric chromosomes. About 80% of males with this type of translocation, which arises almost exclusively de novo, have azoospermia. The translocation is mainly discovered during a consultation for infertility. Finally, unbalanced Y;autosome translocations, with or without other chromosome abnormalities, are seen in children with malformations and/or sexual ambiguity owing to deletions, duplications, or rearrangements. The cases reported here share similarities with those of the first category but concern a chromosome 1 instead of an acrocentric. To our knowledge, this is the first segregation study of such an unbalanced (Y;1) translocation.