Parental mosaicism is a pitfall in preimplantation genetic diagnosis of dominant disorders.

[cowden syndrome]

PCR amplification on single cells is prone to allele drop-out (PCR failure of one allele ), a cause of misdiagnosis in preimplantation genetic diagnosis (PGD ). Owing to this error risk , PGD usually relies on both direct and indirect genetic analyses . When the affected partner is the sporadic case of a dominant disorder , building haplotypes require spermatozoon or polar body testing prior to PGD , but these procedures are cost and time-consuming . A couple requested PGD because the male partner suffered from a dominant Cowden syndrome (CS ). He was a sporadic case , but the couple had a first unaffected child and the non-mutated paternal haplotype was tentatively deduced . The couple had a second spontaneous pregnancy and the fetus was found to carry the at -risk haplotype but not the PTEN mutation . The mutation was present in blood from the affected father , but at low level , confirming the somatic mosaicism . Ignoring the possibility of mosaicism in the CS patient would have potentially led to selection of affected embryos . This observation emphasizes the risk of PGD in families at risk to transmit autosomal-dominant disorder when the affected partner is a sporadic case .