Biallelic variants in PIGN cause ‘multiple congenital anomalies-hypotonia-seizures syndrome type 1' (MCAHS1; OMIM 614080).19, 26 However, a recent review of published cases highlights significant phenotypic heterogeneity.24 Although seizures, developmental delay and hypotonia are always present, other features can include dysmorphisms (low-set ears, micrognathia and distal digital hypoplasia), cerebellar atrophy, nystagmus and diaphragmatic hernia. Here, PIGN is linked to pathologic nystagmus.