Abstracts

Rationale: Genetic approaches are providing evidence for the importance of molecular mechanism in early-onset epileptic encephalopathies (EOEE). Recently, a PIGA germline mutation involved in the first step of the glycosylphosphatidylinositol (GPI) biosynthesis and its somatic mutation responsible for paroxysmal nocturnal hemoglobinuria has been reported in an X-linked family of multiple congenital anomalies and neonatal seizures with poor prognosis. At least two of three patients showed severe myoclonic seizures with suppression-burst on EEG, suggesting early myoclonic encephalopathy (EME). The identification of the PIGA mutation in the EME phenotype prompted screening for this gene in an EOEE patient cohort.Methods: We searched for all PIGA variants identified by whole-exome sequencing using the Illumina HiSeq system in 106 individuals with various EOEE. Patients with ARX, STXBP1, KCNQ2, SCN1A, and SCN2A mutations were excluded. We also tested the hematopoietic cells of the subjects for the absence of GPI-anchored proteins using FACSCalibur flow cytometry.Results: We found two PIGA mutations in two sporadic EOEE cases. Flow cytometry analysis demonstrated reduced CD16 expression (15% and 5% in patients 1 and 2, respectively), which is a GPI-anchored protein, compared with controls. Patient 1 had a hemizygous nonsense mutation, c.1234C>T (p.R412X), which was the same as that in an EME family. He was born after a 33-week gestation by artificial insemination and polyhydramnios. He showed multiple congenital anomalies, i.e., depressed nasal bridge, high-arched palate, hepatomegaly due to hepatoblastoma, and joint contractures. He showed tonic seizures with suppression-burst on EEG at 1 month and was diagnosed with Ohtahara syndrome. MRI in infancy showed brain atrophy, delayed myelination, and abnormal signals in the bilateral thalamus and brainstem. At 6 years, he showed hypotonia, profound intellectual disability, and frequent myoclonus. Patient 2 had a maternally inherited hemizygous missense mutation, c.616A>T (p.I206F) and was born after a 40-week gestation. He had a peculiar face with malar flattening, depressed nasal bridge, short anteverted nose, and joint contractures. He showed myoclonus or spasm-like movement at 3 months. His interictal EEG showed hypsarrhythmia but no ictal discharges. Brain MRI at 2 years showed delayed myelination. He was diagnosed with early-onset West syndrome with cerebral hypomyelination; no SPTAN1 mutation was found. At 8 years, he showed tonic seizures with periodic multifocal spike-and-slow wave complex clusters, similar to suppression-burst on EEG, profound intellectual disability, spastic quadriplegia, and bulbar palsy with gastrostomy and tracheostomy.Conclusions: PIGA mutations cause various EOEE such as EME, Ohtahara syndrome, and West syndrome. Multiple anomalies including a peculiar face, delayed myelination, and myoclonus are key findings in EOEE caused by the PIGA mutation.