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# Hers disease (glycogen storage disease type VI)

In Hers disease liver phosphorylase fails: the child has a large liver and mild drops in blood sugar that improve with age.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Liver](https://durgical.com/en/anatomy/liver/)
- [Portal vein](https://durgical.com/en/anatomy/hepatic-portal-vein/)
- [Hepatic veins](https://durgical.com/en/anatomy/hepatic-veins/)

## In biochemistry

- [Glycogen phosphorylase](https://durgical.com/en/biochemistry/enzymes/glycogen-phosphorylase/)
- [Glycogen](https://durgical.com/en/biochemistry/molecules/glycogen/)

## What it is

Liver glycogen storage disease caused by lack of liver glycogen phosphorylase (PYGL gene). It is usually mild.

## Who gets it

Rare and probably underdiagnosed; commoner in the Old Order Mennonite community (1 in 1,000).

## Causes

- Autosomal recessive inheritance: PYGL gene variants

## Risk factors

- Carrier parents or affected siblings

## Pathophysiology

Without liver phosphorylase, glycogen accumulates in the liver and releases little glucose during fasting. Gluconeogenesis is intact, so hypoglycaemia is mild and accompanied by ketosis; lactate and uric acid are usually normal.

## Symptoms and signs

- Large [abdomen](https://durgical.com/en/anatomy/region/abdomen/) from hepatomegaly in early childhood
- Mild hypoglycaemia with long fasts or illness
- Slow growth
- Tiredness with exercise in some children

## Red flags

- Drowsiness or seizure during an illness with fasting

## Diagnosis

**Clinical**
Child with hepatomegaly, slow growth and mild ketotic hypoglycaemia.

**Tests**
Mildly raised transaminases, fasting ketosis, normal lactate and uric acid. PYGL gene testing (distinguishes GSD VI from GSD IX, phosphorylase kinase).

**Imaging**
Abdominal ultrasound with hepatomegaly.

## Treatment

**Lifestyle**
Avoid long fasts; frequent meals and uncooked cornstarch at bedtime if the metabolic team advises it

**Lifestyle**
Diet with good protein intake

**Follow-up**
Monitoring of growth and [liver](https://durgical.com/en/anatomy/liver/)

## Complications

- Liver fibrosis (rare)
- Hepatic adenomas (rare)

## Prognosis

Good: hepatomegaly and hypoglycaemia usually improve by puberty.

## Test yourself

Think of the answer, then tap the question to see it.

## Which enzyme is missing in Hers disease?

Liver glycogen phosphorylase (PYGL).

## Why is hypoglycaemia mild in Hers disease?

Gluconeogenesis works and makes glucose even though glycogen is not released.

## Which glycogen storage disease resembles type VI and how are they told apart?

Type IX (phosphorylase kinase); they are distinguished by genetic testing.

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## Related conditions

- [Von Gierke disease (glycogen storage disease type I)](https://durgical.com/en/conditions/von-gierke-disease/)
- [Cori disease (glycogen storage disease type III)](https://durgical.com/en/conditions/cori-disease/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Glycogen storage disease type VI: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/glycogen-storage-disease-type-vi/) (MedlinePlus, US National Library of Medicine, 2026); [PYGL gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/pygl/) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Source: https://durgical.com/en/conditions/hers-disease/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/hers-disease/