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At a glance

Glycogen storage disease Type VI (GSD VI) is a type of glycogen storage disease caused by a deficiency in liver glycogen phosphorylase or other components of the associated phosphorylase cascade system. Autosomal recessive inborn error of metabolism of glycogen associated with mild hypoglycemia, hyperlipidemia, and hyperketosis may occur. Lactic acid and uric acid levels may be normal. However, lactic acidosis may occur during fasting. Patients generally have a benign course, and typically present with hepatomegaly and growth retardation early in childhood.

Synonyms

Hers Syndrome; Hers Disease; Glycogen Phosphorylase Deficiency; Hepatic Phosphorylase Kinase Deficiency; Liver Phosphorylase Deficiency; X-Linked Liver Glycogenosis; Glycogenosis Type VI; Phosphorylase b Kinase Deficiency.

History

It is also known as “Hers’ disease,” after Henri G. Hers (23 July 1923-14 December 2008) who was a Belgian physiologist and biochemist, and a professor at the Universite Catholique de Louvain. He characterized this medical condition in 1959. In 1966, he was awarded the Francqui Prize on Biological and Medical Sciences, and in 1975 was awarded the Gairdner Foundation International Award of the Gairdner Foundation.

N.B.: The Francqui Prize is a prestigious Belgian scholarly and scientific prize named after Émile Francqui [1863-1935] who was a Belgian Soldier, Diplomat, Business man, and Philanthropist. Normally annually since 1933, the Francqui Foundation awards it in recognition of the achievements of a scholar or scientist, who at the start of the year had to be under 50. It currently represents a sum of 250,000 Euros and is awarded in the following 3-year rotation of subjects: exact sciences, social sciences or humanities, and biological or medical sciences.

Nature

Inborn error of metabolism consisting of a deficiency of liver phosphorylase (classic form) or other enzyme defects of the phosphorylase cascade system such as phosphorylase b kinase deficiency (formerly GSD IX, GSD VIII by McKusick) and adenosine 3′,5′-cyclic monophosphate (cyclic AMP)-dependent protein kinase deficiency (formerly GSD X).

Incidence

The incidence of GSD VI is approximately 1 case per 65,000 to 85,000 births, which accounts for about 30% of all GSD, of which approximately 75% result from the X-linked recessive form of phosphorylase kinase deficiency. Incidence up to 0.1% in the Mennonite population (3% incidence of specific splice-site mutation in the liver phosphorylase gene of this religious group).

Genetic inheritance

Approximately 75% of these GSD VI cases result from the X-linked recessive forms of phosphorylase kinase deficiency, all other forms are autosomal recessive. It is believed to be inherited as autosomal recessive (classic form; accounts for about 25% of cases) and X-linked recessive form (phosphorylase kinase deficiency). Phosphorylase b kinase genes are multimeric (four different subunits, each coded by a unique gene located on different chromosomes). Different isoforms of each enzyme with differential tissue expression exist.

Pathophysiology

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