Prenatal diagnosis and genetic counseling of uniparental disomy.

Uniparental disomy (UPD) is the inheritance of both homologous chromosomes from a single parent. Most chromosomes involving UPD have no pathogenic effects. However, abnormal phenotypes in cases with UPD can be mainly caused by disrupting genetic imprinting and by uncovering harmful autosomal recessive mutations. The documented phenotypes of UPD associated with imprinted genes include maternal UPD for chromosomes 7, 11, 14, 15, 16, and 20, and paternal UPD for chromosomes 6, 11, 14, 15, and 20. Prenatal awareness of UPD is important to provide accurate genetic counseling and prenatal UPD test is suggested when abnormal fetal ultrasound with suspicious phenotypes for UPD syndromes caused by genetic imprinting disorders or presence of chromosomal aberrations involving the imprinted chromosomes.