Cri du chat syndrome (CdCS) is caused by a deletion of the short arm of chromosome 5. Phenotype depends on the length of the deleted region. The deletion usually occurs de novo. Familial translocation as a cause of CdCS occurs in only 3% of patients. In familial translocations, rearrangements involving chromosome 5 and any other chromosome can occur. Therefore, children with different, unbalanced chromosome complements, could be born in the same family.

Here we report on a family where the mother was a balanced carrier of a translocation 5;9. One child had CdCS with a typical clinical presentation and with a classi­cal 5p deletion in the karyotype. Karyotyping of the mother confirmed the familial origin of this deletion. A sister of the proband had trisomy 5p, with some of the features of this syndrome. Three deceased children proba­bly all had unbalanced rearrangements of chromosomes since they all were mentally retarded. Two healthy girls were carriers of the balanced translocation 5;9, inherited from the mother, and were completely normal.

We conclude that a balanced translocation in a parent could be the origin of different chromosome complements in children from the same family. However, the risk of unbalanced offspring in the presented family was much higher than that described in the literature.