Risk for recombinants in pericentric inversions of the (p11 leads to q21) region of chromosome 18.

A child with female hypospadia complicated by bilateral hydronephrosis, hydroureter, and hydrocolpos was heterozygous for a pericentric inversion of chromosome 18, 46,XX,inv(18)(p11q21). The normal mother and her father had the same inversion. The abnormal phenotype of the girl could be due to undetectable recombination or to a position effect. She had a low level of the enzyme peptidase-A whose locus is on 18q, while her mother and grandfather had normal levels. The two other cases of familial inversions for chromosomes 18 in the literature both involve the same (p11 leads to q21) region. These three families give a tentative figure of at least 10% as the risk for a normal carrier of this pericentric inversion to have an affected offspring due to recombination.