Holoprosencephaly-postaxial polydactyly syndrome

Holoprosencephaly-postaxial polydactyly syndrome (also known as pseudotrisomy 13 syndrome or holoprosencephaly-polydactyly syndrome) is an extremely rare congenital malformation syndrome characterized by the combination of holoprosencephaly (a failure of the forebrain to properly divide into two hemispheres) and postaxial polydactyly (extra digits on the outer side of the hands and/or feet). The condition primarily affects the central nervous system and the limbs, and may also involve craniofacial abnormalities such as midline facial defects (cyclopia, cebocephaly, median cleft lip, or hypotelorism), microcephaly, and other structural brain malformations. Cardiac defects and other visceral anomalies have also been reported in some cases. The clinical presentation overlaps significantly with trisomy 13 (Patau syndrome), but affected individuals have a normal karyotype, which is why the condition has been referred to as pseudotrisomy 13. The severity of holoprosencephaly can range from alobar (most severe) to lobar forms, and the prognosis is generally very poor, with most affected infants dying in the neonatal period or early infancy. The condition is typically identified prenatally or at birth based on the characteristic combination of brain and limb malformations. There is no specific curative treatment; management is supportive and symptomatic, focusing on comfort care and addressing individual medical complications as they arise. Genetic counseling is recommended for affected families.

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