Differential diagnosis of pseudotrisomy 13 syndrome

Pseudotrisomy 13 syndrome is determined by the combination of three findings: holoprosencephaly, postaxial polydactyly, and a normal karyotype. We report two cases of a prenatal diagnosis of pseudotrisomy 13 syndrome and one case of a suspected hydrolethalus syndrome, another disorder with a similar phenotype and karyotype. Thorough literature search yields limited information, and the genetic cause of this syndrome remains unclear; however, it is thought to be monogenic and inherited as an autosomal recessive disorder. Given the poor prognosis and the easily recognizable malformations associated with this disease, it is important to perform an early diagnosis.