Mutations in the phosphatidylinositol glycan C (PIGC) gene are associated with epilepsy and intellectual disability.
Of our 1400 exome-studied patients, 67% originate from consanguineous families. ∼80% suffer from variable degree of intellectual disability (ID). The search for disease causing genes using homozygosity mapping was progressing slowly until 2010, then markedly accelerated by the introduction of exome analysis.



To identify the disease causing mutation(s) in three patients from two unrelated families who suffered from global developmental delay, severe ID and drug-responsive seizure disorder.



Exome analysis was performed in DNA of the three patients. The identifiedPIGCvariants were generated and transfected into PIGC-defective mouse cells and the restoration of the surface expression of mouse CD90, CD48 and FLAER was assessed using flow cytometry. The expression of these proteins was also studied on the surface of patients' leucocytes.



ThreePIGCmutations were identified; homozygous p.L189W in one family and compound heterozygosity for p.L212P/p.R21X variants in another.PIGCparticipates in the biosynthesis of the glycosylphosphatidylinositol (GPI) anchor which tethers proteins to plasma membrane. In cells lacking PIGC protein, which were transfected with each of the PIGC variants, we detected a clear reduction of surface expression of GPI-anchored proteins. Furthermore, analyses of patients' leucocytes showed significant and constant decrease of CD16 surface expression in granulocytes, and moderate decrease of CD14, CD55, CD59 and FLAER levels.



PIGCjoins the list of genes in which mutations result in defective biosynthesis of GPI anchoring, manifesting by global developmental delay and seizure disorder. The lack of specific biomarker dictates exome sequencing as the diagnostic procedure of choice in similar patients.
Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.|Pediatric Neurology Unit, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.
Simon
S
Edvardson
WPI Immunology Frontier Research Center and Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan.
Yoshiko
Y
Murakami
CHU Sainte-Justine Research Center, University of Montreal, Montreal, Québec, Canada.
Thi Tuyet Mai
TT
Nguyen
Department of Pediatrics and Genetics, Makassed Hospital, Al-Quds Medical School, Jerusalem, Israel.
Maher
M
Shahrour
Department of Microbiology and Immunology, CHU Sainte Justine, Montreal, Québec, Canada.
Anik
A
St-Denis
Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.
Avraham
A
Shaag
Department of Pediatrics and Genetics, Makassed Hospital, Al-Quds Medical School, Jerusalem, Israel.
Nadira
N
Damseh
CHU Sainte-Justine Research Center, University of Montreal, Montreal, Québec, Canada.|Department of Microbiology and Immunology, CHU Sainte Justine, Montreal, Québec, Canada.|Department of Microbiology Infectiology and Immunology, University of Montreal, Montreal, Québec, Canada.|Department of Pediatrics, University of Montreal, Montreal, Québec, Canada.
Françoise
F
Le Deist
Department of Medicine, Centre for Hematology and Regenerative Medicine, Karolinska Institutet, Karolinska University Hospital Huddinge, Stockholm, Sweden.
Yenan
Y
Bryceson
Department of Pediatrics and Genetics, Makassed Hospital, Al-Quds Medical School, Jerusalem, Israel.
Bassam
B
Abu-Libdeh
CHU Sainte-Justine Research Center, University of Montreal, Montreal, Québec, Canada.|Department of Pediatrics, University of Montreal, Montreal, Québec, Canada.
Philippe M
PM
Campeau
WPI Immunology Frontier Research Center and Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan.
Taroh
T
Kinoshita
Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.
Orly
O
Elpeleg
D000015:Abnormalities, Multiple; D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D002658:Developmental Disabilities; D004827:Epilepsy / Q000235:genetics* / Q000503:physiopathology; D059472:Exome / Q000235:genetics; D005260:Female; D056726:Genetic Association Studies; D006602:Hexosyltransferases / Q000235:genetics*; D006720:Homozygote; D006801:Humans; D008607:Intellectual Disability / Q000235:genetics* / Q000503:physiopathology; D008297:Male; D008565:Membrane Proteins / Q000235:genetics*; D051379:Mice; D009154:Mutation; D010375:Pedigree
D008565:Membrane Proteins; D006602:Hexosyltransferases; C101351:PIGC protein, human
Glycosylphosphatidylinositol anchoring; Intellectual disability