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Functional evaluation of 16 SCHAD missense variants: Only amino acid substitutions causing congenital hyperinsulinism of infancy lead to loss‐of‐function phenotypes in vitro
Author(s) -
Velasco Kelly,
StLouis Johanna L.,
Hovland Henrikke N.,
Thompson Nels,
Ottesen Åsta,
Choi Man Hung,
Pedersen Line,
Njølstad Pål R.,
Arnesen Thomas,
Fjeld Karianne,
Aukrust Ingvild,
Myklebust Line M.,
Molven Anders
Publication year - 2021
Publication title -
journal of inherited metabolic disease
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.462
H-Index - 102
eISSN - 1573-2665
pISSN - 0141-8955
DOI - 10.1002/jimd.12309
Subject(s) - missense mutation , biology , phenotype , loss function , hek 293 cells , enzyme , gene , population , genetics , biochemistry , medicine , environmental health
Short‐chain 3‐hydroxyacyl‐CoA dehydrogenase (SCHAD), encoded by the HADH gene, is a ubiquitously expressed mitochondrial enzyme involved in fatty acid oxidation. This protein also plays a role in insulin secretion as recessive HADH mutations cause congenital hyperinsulinism of infancy (CHI) via loss of an inhibitory interaction with glutamate dehydrogenase (GDH). Here, we present a functional evaluation of 16 SCHAD missense variants identified either in CHI patients or by high‐throughput sequencing projects in various populations. To avoid interactions with endogenously produced SCHAD protein, we assessed protein stability, subcellular localization, and GDH interaction in a SCHAD knockout HEK293 cell line constructed by CRISPR‐Cas9 methodology. We also established methods for efficient SCHAD expression and purification in E. coli , and tested enzymatic activity of the variants. Our analyses showed that rare variants of unknown significance identified in populations generally had similar properties as normal SCHAD. However, the CHI‐associated variants p.Gly34Arg, p.Ile184Phe, p.Pro258Leu, and p.Gly303Ser were unstable with low protein levels detectable when expressed in HEK293 cells. Moreover, CHI variants p.Lys136Glu, p.His170Arg, and p.Met188Val presented normal protein levels but displayed clearly impaired enzymatic activity in vitro, and their interaction with GDH appeared reduced. Our results suggest that pathogenic missense variants of SCHAD either make the protein target of a post‐translational quality control system or can impair the function of SCHAD without influencing its steady‐state protein level. We did not find any evidence that rare SCHAD missense variants observed only in the general population and not in CHI patients are functionally affected.