Excess of mental retardation and/or congenital malformation in reciprocal translocations in man.

In this report the Leuven experience (1970-1984) on reciprocal translocations is summarized. A total of 153 unrelated index patients, carriers of different types of reciprocal translocations, and their families were investigated. Familial reciprocal, apparently balanced translocations were found in 75 unrelated families bringing the total numbers of translocation carrier parents and their offspring to 132 and 445, respectively. In 61.5% of the patients the reciprocal translocation was detected after the birth of a malformed child with unbalanced karyotype or through investigation because of recurrent spontaneous abortions, stillbirths, or infertility. In 41 patients (28 familial and 13 de novo), however, the reciprocal balanced translocation was found to be associated with mental retardation and/or congenital malformations (MR/CM) which is significantly higher than expected. This excess of MR/CM in de novo and familial balanced translocation carriers is illustrated and discussed.