Invited editorial comment-the human phenotype of germlinePIGAmutations

Congenital diaphragmatic hernia in siblings with PIGA-related congenital disorder of glycosylation

There are over 150 proteins involved in glycosylphosphatidylinositol (GPI)-anchored protein biosynthesis, a class within the larger category of congenital disorders of glycosylation (CDG). Pathogenic variants identified in phosphatidylinositol glycan class A protein (PIGA) are associated with X-linked PIGA-CDG, a GPI-anchor defect. The disease has primarily been characterized by hypotonia, epilepsy, and global developmental delay; however, only 89 known cases are reported, so the phenotypic spectrum has likely not yet been fully delineated. Congenital diaphragmatic hernia (CDH) has been reported in patients with various GPI-anchor related defects but has only been described in one prior individual with PIGA-CDG. Here, we describe the second and third reported cases of CDH in two brothers with PIGA-CDG caused by a pathogenic missense variant in PIGA: c.355C > T, p.R119W. Chromosomal microarray and whole exome sequencing did not reveal another plausible explanation for the CDH. We relate our patients' clinical features to the single previously reported individual with CDH and PIGA-CDG. We then compare this case series with the subset of individuals with CDH and other GPI-anchor defects. These findings suggest that CDH should be considered in the phenotypic disease spectrum of PIGA-CDG.

PIGA Mutations Can Mimic Neonatal Hemochromatosis

Neonatal hemochromatosis (NH), one of the most common causes of liver failure in the neonate, often causes fetal loss or death during the neonatal period. Most cases are thought to be due to gestational alloimmune disease; however, other rare causes have been reported. NH is generally considered congenital and familial but not heritable. We present an infant diagnosed with NH whose clinical course differed significantly from that of most NH cases: at 11 months of age he had normal levels of liver enzymes, ferritin, and bilirubin, and normal neurodevelopment. This term male infant was born with a history of intrauterine growth restriction, oligohydramnios, and pericardial effusion. On day of life 1, he had hyperbilirubinemia and transaminitis; on day of life 3, ferritin was elevated; and on day of life 9, an MRI revealed iron deposits in the liver and renal cortex. Phenotypic features prompted a genetics consult. Whole-exome sequencing revealed a variant in the phosphatidylinositol glycan biosynthesis class A protein (PIGA) gene. Germ-line PIGA mutations are generally thought to be lethal in utero; however, there are reports of infants with PIGA mutations associated with dysmorphic features, neurologic manifestations, biochemical perturbations, and systemic iron overload; development can be normal up to 6 months of age. Because of the differences between infants with NH versus PIGA germ-line mutations in inheritance, prognosis, and natural history of disease, we propose that PIGA gene testing should be considered when evaluating newborns who present with NH.

A novel PIGA mutation in a family with X-linked, early-onset epileptic encephalopathy

Early-onset epileptic encephalopathies (EOEEs) are severe and intractable infantile-onset epilepsies with progressive intellectual disability and other associated neurologic comorbidities. Whole-exome sequencing (WES) was recently used to determine the causative gene mutations in individuals with unclassified EOEEs. The present study used WES to determine the causative variant in a family with X-linked, EOEE. One potential variant (c. 427A>G, NM_002641.3; p.Lys143Glu, NP_002632.1) of the gene encoding phosphatidylinositol glycan biosynthesis class A protein (PIGA; PIGA) was found, which was verified by Sanger sequencing. The functional effect of this PIGA mutation was assessed by the surface expression levels of glycosylphosphatidylinositol-anchored proteins on blood cells: CD16 on red blood cells was significantly decreased in the proband (by 11.0%) and his mother (by 15.6%). This is the second report of a less-severe form of PIGA deficiency.

A recurrent germline mutation in the PIGA gene causes Simpson-Golabi-Behmel syndrome type 2

Hypomorphic germline mutations in the PIGA (phosphatidylinositol glycan class A) gene recently were recognized as the cause of a clinically heterogeneous spectrum of X-linked disorders including (i) early onset epileptic encephalopathy with severe muscular hypotonia, dysmorphism, multiple congenital anomalies, and early death ("MCAHS2"), (ii) neurodegenerative encephalopathy with systemic iron overload (ferro-cerebro-cutaneous syndrome, "FCCS"), and (iii) intellectual disability and seizures without dysmorphism. Previous studies showed that the recurrent PIGA germline mutation c.1234C>T (p.Arg412*) leads to a clinical phenotype at the most severe end of the spectrum associated with early infantile lethality. We identified three additional individuals from two unrelated families with the same PIGA mutation. Major clinical findings include early onset intractable epileptic encephalopathy with a burst-suppression pattern on EEG, generalized muscular hypotonia, structural brain abnormalities, macrocephaly and increased birth weight, joint contractures, coarse facial features, widely spaced eyes, a short nose with anteverted nares, gingival overgrowth, a wide mouth, short limbs with short distal phalanges, and a small penis. Based on the phenotypic overlap with Simpson-Golabi-Behmel syndrome type 2 (SGBS2), we hypothesized that both disorders might have the same underlying cause. We were able to confirm the same c.1234C>T (p.Arg412*) mutation in the DNA sample from an affected fetus of the original family affected with SGBS2. We conclude that the recurrent PIGA germline mutation c.1234C>T leads to a recognizable clinical phenotype with a poor prognosis and is the cause of SGBS2.