HOMOZYGOSITY FOR PERICENTRIC INVERSIONS OF CHROMOSOME-9 - PRENATAL-DIAGNOSIS OF 2 CASES

The finding of homozygosity for a pericentric inversion of chromosome 9 [inv(9)] is rare, and previously has not been reported at prenatal d iagnosis. We describe mio unrelated cases of homozygosity for inv(9) i dentified in amniocytes. In each case, both parents were heterozygotes for the inv(9); 46,XX,inv(9)(p11q13) and 36,XY,inv(9) (p11q13). Case 1 resulted in a normal term infant who at age 5 years was phenotypical ly and developmentally normal, Case 2 was referred for severe intraute rine growth retardation (IUGR) and oligohydramnios, and subsequently e xpired in utero. Even though inv(9) is a normal chromosome variant wit h a frequency of 1 to 3% in the general population, the finding of hom ozygosity for inv(9) and IUGR in this fetus suggested the possibility of uniparental disomy (UPD), Molecular studies confirmed the presence of both parental inv(9) chromosomes, excluding the possibility of chro mosome 9 UPD as the cause of IUGR in this fetus. Presumably, inv(9) ho mozygosity results from the high frequency of inv(9) heterozygosity, a nd is a normal variant, However, until the effects of UPD for chromoso me 9 are established parental karyotypes and, where appropriate, molec ular studies should be performed to exclude UPD. In addition, more rep orts of inv(9) homozygosity detected prenatally are needed to assess i ts frequency and outcome.