ABSTRACT
Phosphoglucomutase 3 (PGM3) deficiency is a rare congenital disorder of glycosylation. Most of patients with autosomal recessive hypomorphic mutations in PGM3 encoding for phosphoglucomutase 3 present with eczema, skin and lung infections, elevated serum IgE, as well as neurological and skeletal features. A few PGM3-deficient patients suffer from a more severe disease with nearly absent T cells and severe skeletal dysplasia. We performed targeted next-generation sequencing on two kindred to identify the underlying genetic etiology of a severe combined immunodeficiency with developmental defect. We report here two novel homozygous missense variants (p.Gly359Asp and p.Met423Thr) in PGM3 identified in three patients from two unrelated kindreds with severe combined immunodeficiency, neurological impairment, and skeletal dysplasia. Both variants segregated with the disease in the two families. They were predicted to be deleterious by in silico analysis. PGM3 enzymatic activity was found to be severely impaired in primary fibroblasts and Epstein-Barr virus immortalized B cells from the kindred carrying the p.Met423Thr variant. Our findings support the pathogenicity of these two novel variants in severe PGM3 deficiency.
Subject(s)
Abnormalities, Multiple/genetics , Bone Diseases, Developmental/genetics , Limb Deformities, Congenital/genetics , Nervous System Diseases/genetics , Phosphoglucomutase/genetics , Severe Combined Immunodeficiency/genetics , Child, Preschool , Face/abnormalities , Female , Humans , Infant , Infant, Newborn , MaleABSTRACT
Our aim was to identify the product formed by sedoheptulokinase and to understand the mechanism of formation of erythritol in patients with sedoheptulokinase deficiency. Mouse recombinant sedoheptulokinase was found to be virtually specific for sedoheptulose and its reaction product was identified as sedoheptulose 7-phosphate. Assays of sedoheptulose in plant extracts disclosed that this sugar is present in carrots ( approximately 7mumol/g) and in several fruits. Sedoheptulose 1-phosphate is shown to be a substrate for aldolase B, which cleaves it to dihydroxyacetone-phosphate and erythrose. This suggests that, in patients deficient in sedoheptulose-7-kinase, sedoheptulose is phosphorylated by fructokinase to sedoheptulose 1-phosphate. Cleavage of the latter by aldolase B would lead to the formation of erythrose, which would then be reduced to erythritol.
Subject(s)
Erythritol/biosynthesis , Phosphotransferases (Alcohol Group Acceptor)/metabolism , Sugar Phosphates/metabolism , Animals , Fructose-Bisphosphate Aldolase/chemistry , Fruit/enzymology , Humans , Mice , Phosphotransferases (Alcohol Group Acceptor)/chemistry , Phosphotransferases (Alcohol Group Acceptor)/deficiency , Phosphotransferases (Alcohol Group Acceptor)/genetics , Plant Proteins/chemistry , Plant Proteins/genetics , Plant Proteins/metabolism , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Sugar Phosphates/chemistry , Transcription Factors/chemistry , Transcription Factors/deficiency , Transcription Factors/genetics , Vegetables/enzymologyABSTRACT
To identify the sequence of hydroxyacid-oxoacid transhydrogenase (HOT), responsible for the oxidation of 4-hydroxybutyrate in mammalian tissues, we have purified this enzyme from rat liver and obtained partial sequences of proteins coeluting with the enzymatic activity in the last purification step. One of the identified proteins was 'iron-dependent alcohol dehydrogenase', an enzyme encoded by a gene present on human chromosome 8q 13.1 and distantly related to bacterial 4-hydroxybutyrate dehydrogenases. The identification of this protein as HOT was confirmed by showing that overexpression of the mouse homologue in HEK cells resulted in the appearance of an enzyme catalyzing the alpha-ketoglutarate-dependent oxidation of 4-hydroxybutyrate to succinate semialdehyde.
