Glycogen storage disease type VI

Glycogen storage disease type VI, also called GSD VI or Hers disease, is an inherited disorder in which liver cells cannot break down glycogen, the stored form of sugar, because the liver form of the enzyme glycogen phosphorylase does not work properly. The gene involved is PYGL, and the condition is passed on in an autosomal recessive pattern. The first sign is usually an enlarged liver in infancy or early childhood, and during long periods without food a child may have low blood sugar or ketones in the blood. Growth can be slower than in other children, and some have mild delays in motor skills, but signs tend to improve with age and most adults have no related health problems. The exact prevalence is unknown, though the disorder is more common in the Old Order Mennonite population.