Glycogen Storage Disease Type Ib
Summary
GSD Ib shares the fasting hypoglycaemia and liver problems of GSD Ia (they affect the same metabolic pathway), but adds a distinctive complication: neutropenia and neutrophil dysfunction. The SLC37A4 gene encodes the transporter that moves glucose-6-phosphate into the endoplasmic reticulum where it can be processed — a different step in the same pathway as GSD Ia.
Practical takeaway
This matters when planning children. Carrier testing through a GP or genetic counselling service can determine your partner's status. The encouraging context: GSD Ib is treatable with dietary management plus targeted therapy for neutropenia. Realised does not calculate reproductive risk or advise on reproductive decisions.
Evidence detail
What Carrier Status Means For You
You are not affected. One working copy of SLC37A4 produces sufficient transporter for normal glucose metabolism and neutrophil function. Standard 25/50/25 recessive inheritance applies if your partner is also a carrier.
Population Context
GSD Ib occurs across all ethnic groups without dramatic population-specific enrichment. Incidence is approximately 1 in 300,000-500,000 births, accounting for roughly 20% of all GSD type I cases.
Limitations
23andMe tests 2 of over 90 known pathogenic SLC37A4 variants. Coverage is limited. A "not detected" result provides only modest reduction in carrier risk. Comprehensive screening recommended if partner is a known carrier.
Sources (4)
- ClinVar: SLC37A4 pathogenic/likely pathogenic variant database↗
- OMIM: #232220 (Glycogen Storage Disease Ib)↗
- Wortmann et al. (2020), "Empagliflozin for glycogen storage disease type Ib" — NEJM↗
- Kishnani et al. (2014), "Diagnosis and management of glycogen storage disease type I" — Genetics in Medicine↗