Early infantile epileptic-dyskinetic encephalopathy due to biallelic PIGP mutations

Annalisa Vetro; Tiziana Pisano; Silvia Chiaro; Elena Procopio; Azzurra Guerra; Elena Parrini; Davide Mei; Simona Virdò; Giusi Mangone; Chiara Azzari; Renzo Guerrini

doi:10.1212/NXG.0000000000000387

Early infantile epileptic-dyskinetic encephalopathy due to biallelic PIGP mutations

Neurol Genet. 2020 Jan 2;6(1):e387. doi: 10.1212/NXG.0000000000000387. eCollection 2020 Feb.

Authors

Affiliation

¹ Pediatric Neurology (A.V., T.P., S.C., E. Parrini, D.M., S.V., R.G.), Neurogenetics and Neurobiology Unit and Laboratories, Meyer Children's Hospital, University of Florence; Metabolic and Muscular Unit (E. Procopio), Meyer Children's Hospital, University of Florence; Department of Medical and Surgical Science (A.G.), University of Modena and Reggio Emilia; Pediatric Immunology (G.M., C.A.), Department of Health Sciences, Meyer Children's Hospital, University of Florence; and IRCCS Stella Maris (R.G.), Pisa, Italy.

Abstract

Objective: To describe clinical, biochemical, and molecular genetic findings in a large inbred family in which 4 children with a severe early-onset epileptic-dyskinetic encephalopathy, with suppression burst EEG, harbored homozygous mutations of phosphatidylinositol glycan anchor biosynthesis, class P (PIGP), a member of the large glycosylphosphatidylinositol (GPI) anchor biosynthesis gene family.

Methods: We studied clinical features, EEG, brain MRI scans, whole-exome sequencing (WES), and measured the expression of a subset of GPI-anchored proteins (GPI-APs) in circulating granulocytes using flow cytometry.

Results: The 4 affected children exhibited a severe neurodevelopmental disorder featuring severe hypotonia with early dyskinesia progressing to quadriplegia, associated with infantile spasms, focal, tonic, and tonic-clonic seizures and a burst suppression EEG pattern. Two of the children died prematurely between age 2 and 12 years; the remaining 2 children are aged 2 years 7 months and 7 years 4 months. The homozygous c.384del variant of PIGP, present in the 4 patients, introduces a frame shift 6 codons before the expected stop signal and is predicted to result in the synthesis of a protein longer than the wild type, with impaired functionality. We demonstrated a reduced expression of the GPI-AP CD16 in the granulocytic membrane in affected individuals.

Conclusions: PIGP mutations are consistently associated with an epileptic-dyskinetic encephalopathy with the features of early infantile epileptic encephalopathy with profound disability and premature death. CD16 is a valuable marker to support a genetic diagnosis of inherited GPI deficiencies.