Abstracts

Rationale: Glyocosylphosphatidylinostiol (GPI) is a complex glycolipid added post-translationally to proteins that serves to tether them to the outer leaflet of the cellular membrane. Inherited GPI-anchor deficiencies (IGD) are a subclass of congenital disorders of glycosylation (CDG) caused by pathogenic variants in phosphotidylinositol glycan (PIG) genes, responsible for GPI biosynthesis. The phenotypic spectrum of IGDs includes infantile epileptic encephalopathy. To date, five cases of IGD have been reported in association with compound heterozygous or homozygous missense variants in PIGW, which encodes an enzyme involved in the addition of an acyl-chain to inositol in an early step of GPI biogenesis 1-4. Here, we present the detailed electroclinical phenotypes of three siblings with early-onset encephalopathy and epilepsy, associated with compound heterozygosity in PIGW. Methods: Phenotypes were characterized by clinical assessment, review of charts, radiological studies, electroencephalography (EEG) recordings, pathology specimens, and parental interview. Results: Three siblings (table) born to non-consanguineous parents each presented between 2 to 3 months of age with focal seizures, characterized by tonic stiffening then hemi-clonic or bilateral clonic jerking. Interictal EEG was significant for medium amplitude multifocal spikes most abundant in the posterior quadrants. Ictal EEG showed focal-onset attenuation with overriding fast activity and/or rhythmic epileptiform activity in the right or left centro-parietal regions with hemispheric or bi-hemispheric spread. All three children developed hypsarrhythmia and epileptic spasms by age 4 to 6 months. Pyridoxine was tried and was ineffective. Seizure frequency improved in response to a combination of vigabatrin, clobazam, and the ketogenic diet. However, the interictal EEG gradually worsened to an asynchronous discontinuous high-amplitude background (Figures 1 and 2).The infants were hypotonic and developmentally delayed from birth, but further regression was noticed at the onset of seizures with loss of visual and auditory attention and social smile. Inability to take adequate nutrition enterally and severe gastroesophageal reflux led to placement of gastrostomy tubes and Nissen fundoplication procedures in all children. Over time, they developed progressive respiratory failure with ventilator dependence. Patient 3 developed cardiomyopathy at 26 months of age. Patient 1 one died from septic shock from Pseudomonas aeruginosa and Candida parapsilosis infections at 2 years of age. Patients 2 and 3 remain profoundly neurodevelopmentally impaired at last follow up, 8 years old and 3.5 years old, respectively. All three children had similar facial dysmorphisms, including a depressed nasal bridge, anterverted nares, long philtrum, high arched palate, tenting of upper lip, hypodontia, and upslanting palpebral fissures with a prominent forehead. Magnetic resonance imaging (MRI) showed progressive cortical and cerebellar progressive atrophy with hypomyelination and thinning of the corpus callosum. Brain pathology of patient 1 at autopsy showed diffuse spongiform leukoencephalopathy with subventricular gliosis and neuronal loss in the hippocampus and cerebellum. Extensive metabolic evaluations demonstrated variable elevation in serum alkaline phosphatase (AP) levels at different points in the clinical course. Karyotype and chromosomal microarray were uninformative. Whole exome sequencing revealed two missense variants in PIGW: p.Arg36Gly (paternally inherited) and p.Pro257Leu (maternally inherited). The pPro257Leu variant is absent from gnomAD. The p.Arg36Gly variant has a minor allele frequency of 2×10−4 and been reported homozygous in a case of fetal demise with features consistent with an IGD6. In silico analysis predicted each of these variants to be deleterious with high probability (polyphen-2, > 0.986). Conclusions: PIGW IGD should be considered among the causes of infantile onset developmental and epileptic encephalopathy. While serum AP levels may provide a biomarker to suggest the diagnosis, levels are not universally elevated, as has been previously reported2. We found this to be the case even in a given patient over time. In contrast to other reports, we did not find pyridoxine to be effective5, but in agreement with a report on PIGA-associated epilepsy7, we did find ketogenic diet to be very helpful in reducing the seizure frequency There was clinical and electrographic deterioration over time independent of seizure control, highlighting the importance of the underlying metabolic disorder in disease progression.References:1. Chiyonobu T, Inoue N, Morimoto M, Kinoshita T, Murakami Y. Glycosylphosphatidylinositol (GPI) anchor deficiency causedby mutations in PIGW is associated with west syndrome and hyperphosphatasia with mental retardation syndrome. J Med Genet 2014;51:203e7.2. Hogrebe M,Murakami Y,Wild M ,et.al. A novel mutation in PIGW causes glycosylphosphatidylinositol deficiency without hyperphosphatoasia. American journal of medical genetics 2016; 170A:3319-33223. Gretchen Kissel Foskett,Edgar et.al.; Use of flow cytometry for diagnosis of epilepsy associated with homozygous PIGW variants. Pediatric Neurology 85 (2018) 67-704. Li’na Fu, Yan Liu et.al. Mutations in the PIGW gene associated with hyperphophatasia and mental retardation syndrome: a case report; BMC Pediatrics (2019) 19:685. Kuku I, Takahashi Y, et.al.; Vitamin B6- responsive epilepsy due to inherited GPI deficiency. Neurology 2013; 81 (16)6. Meier N, Bruder E, et.al. Exome sequencing of fetal anomaly syndromes: novel phenotype-genotype discoveries. Eur J Hum Genet. 2019 May;27(5):730-737. doi: 10.1038/s41431-018-0324-y. Epub 2019 Jan 24. PubMed PMID: 30679815.7. Charuta Joshi, Diana Kolbe, et.al.; Ketogenic diet- a novel treatment for early epileptic encephalopathy due to PIGA deficiency; Brain and Development 38 (2016) 848-851 Funding: No funding