Partial trisomy 13q22→qter and monosomy 18q21→qter as a result of familial translocation

We report on a patient with a partial trisomy of chromosome 13q22-->qter and partial monosomy of chromosome 18q21-->qter showing distinct malformations. The phenotype of this unbalanced karyotype has not been previously described. The proband had a craniofacial dysmorphism, neck pterygium, closed fists with overlapping fingers, cutaneous appendix of the left fist, equinovarus and postaxial hexadactyly of the feet, atrial septum defect, unilateral cryptorchidism and hypertrophic pyloric stenosis. Using fluorescence in situ hybridization (FISH) the father's karyotype 46,XY.ish t(13;18)(13pter-->13q22::18q21-->18qter; 18pter-->18q21::13q22-->13qter) and the child's 46,XY.ish der(18)(18pter-->18q21::13q22-->13qter)pat were established. The mother's karyotype was normal. A risk of unbalanced offspring in carriers of a balanced reciprocal translocation depends on the length and genetic constitution of the exchanged segments. Risk figures should come only from empirical data. A phenotypically normal child with a balanced or normal karyotype could be born in the case of alternate segregation. Amniocentesis should therefore be recommended in any further pregnancy.