Further delineation of PIGB-related early infantile epileptic encephalopathy.

Pathogenic variants in phosphatidylinositol glycan anchor biosynthesis class B (PIGB) gene have been first described as the cause of early infantile epileptic encephalopathy 80 (EIEE-80) in 2019. This disorder, an inherited glycosylphosphatidylinositol deficiency, is associated with a complex neurologic phenotype, including developmental delay, early-onset epilepsy and peripheral neuropathy. We report on a 5 year-old girl born from consanguineous parents, manifesting severe global developmental delay with absent speech, mixed peripheral polyneuropathy, hypotonia, bilateral equino-varo-supinated-cavus foot, early-onset scoliosis, elevated serum alkaline phosphatase and a single episode of febrile status epilepticus. Hypomyelination was documented on brain MRI. Whole-exome sequencing (WES) disclosed the likely pathogenic biallelic PIGB NM_004855.4: c.463G > C, p.(Asp155His) missense variant. In our patient, while other characteristic clinical, neuroimaging and laboratory findings (as described in the first research paper) were present, seizures were not a major clinical issue, thus contributing to our knowledge on this ultra-rare disorder.