PHKA2 variants expand the phenotype of phosphorylase B kinase deficiency to include patients with ketotic hypoglycemia only

Anne Benner, Yazeid Alhaidan, Matthew A. Lines, Klaus Brusgaard, Diva D. De Leon, Rebecca Sparkes, Anja L. Frederiksen, Henrik T. Christesen*

*Corresponding author for this work

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Abstract

Idiopathic ketotic hypoglycemia (IKH) is a diagnosis of exclusion with glycogen storage diseases (GSDs) as a differential diagnosis. GSD IXa presents with ketotic hypoglycemia (KH), hepatomegaly, and growth retardation due to PHKA2 variants. In our multicenter study, 12 children from eight families were diagnosed or suspected of IKH. Whole-exome sequencing or targeted next-generation sequencing panels were performed. We identified two known and three novel (likely) pathogenic PHKA2 variants, such as p.(Pro869Arg), p.(Pro498Leu), p.(Arg2Gly), p.(Arg860Trp), and p.(Val135Leu), respectively. Erythrocyte phosphorylase kinase activity in three patients with the novel variants p.(Arg2Gly) and p.(Arg860Trp) were 15%–20% of mean normal. One patient had short stature and intermittent mildly elevated aspartate aminotransferase, but no hepatomegaly. Family testing identified two asymptomatic children and 18 adult family members with one of the PHKA2 variants, of which 10 had KH symptoms in childhood and 8 had mild symptoms in adulthood. Our study expands the classical GSD IXa phenotype of PHKA2 missense variants to a continuum from seemingly asymptomatic carriers, over KH-only with phosphorylase B kinase deficiency, to more or less complete classical GSD IXa. In contrast to typical IKH, which is confined to young children, KH may persist into adulthood in the KH-only phenotype of PHKA2.

Original languageEnglish
JournalAmerican Journal of Medical Genetics. Part A
Volume185
Issue number10
Pages (from-to)2959-2975
ISSN1552-4825
DOIs
Publication statusPublished - Oct 2021

Keywords

  • glycogen storage disease
  • inborn errors of metabolism
  • ketotic hypoglycemia
  • next-generation sequencing
  • whole-exome sequencing

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