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J Med Genet. 2017 Mar;54(3):196-201. doi: 10.1136/jmedgenet-2016-104202. Epub 2016 Sep 30.

Mutations in the phosphatidylinositol glycan C (PIGC) gene are associated with epilepsy and intellectual disability.

Author information

1
Monique and Jacques Roboh Department of Genetic Research, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.
2
Pediatric Neurology Unit, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.
3
WPI Immunology Frontier Research Center and Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan.
4
CHU Sainte-Justine Research Center, University of Montreal, Montreal, Québec, Canada.
5
Department of Pediatrics and Genetics, Makassed Hospital, Al-Quds Medical School, Jerusalem, Israel.
6
Department of Microbiology and Immunology, CHU Sainte Justine, Montreal, Québec, Canada.
7
Department of Microbiology Infectiology and Immunology, University of Montreal, Montreal, Québec, Canada.
8
Department of Pediatrics, University of Montreal, Montreal, Québec, Canada.
9
Department of Medicine, Centre for Hematology and Regenerative Medicine, Karolinska Institutet, Karolinska University Hospital Huddinge, Stockholm, Sweden.

Abstract

BACKGROUND:

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.

OBJECTIVES:

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.

METHODS:

Exome analysis was performed in DNA of the three patients. The identified PIGC variants 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.

RESULTS:

Three PIGC mutations were identified; homozygous p.L189W in one family and compound heterozygosity for p.L212P/p.R21X variants in another. PIGC participates 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.

CONCLUSIONS:

PIGC joins 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.

KEYWORDS:

Glycosylphosphatidylinositol anchoring; Intellectual disability

PMID:
27694521
DOI:
10.1136/jmedgenet-2016-104202
[Indexed for MEDLINE]

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