Invited editorial comment--The human phenotype of germline PIGA mutations.

Two research groups have published reports on PIGA (phosphatidylinositol glycan class A) mutations that validate and extend our understanding of the range of phenotypes of this phenotypic spectrum. One report is primarily confirmatory of the discovery in 2012 that mutations in this gene cause a phenotype of dysmorphic features, neurologic manifestations, and biochemical perturbations. The second report describes an intriguing family with a phenotypically distinct neurological picture, distinguished primarily by CNS iron accumulation. These reports address important lessons in judging causality in the exome age and bear on the question of syndrome nomenclature.