Glycogen Storage Disease: Type Ib

Glycogen storage disease type Ib (GSD Ib) is an inherited disorder caused by the deficiency of an enzyme called glucose-6-phosphate translocase which acts as a transporter for the substrate of G6Pase. With defective enzyme function, individuals with GSD type Ib cannot maintain blood glucose levels during fasting and will develop low blood sugar. Symptoms become obvious as early as three to four months after birth and affected infants commonly present with low blood sugar, seizures, high lactic acid level, high uric acid and lipid levels in blood and enlarged liver. As they grow older, poor height and weight growth is noted. Kidney disease, high blood pressure in the lungs and decreased bone density are complications that can also occur as individuals grow older. With proper dietary management and careful medical surveillance, GSD Ib patients can live a normal lifespan. GSD Ib is caused by mutations in the SLC37A4 gene.

GSD Ib is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a mutation in the gene for a person to have the genetic disease. Both parents must be carriers of a mutation in the gene in order to be at risk to have an affected child. The child must inherit a mutation from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

There are no signs or symptoms associated with being a carrier for GSD Ib. However, the risk to have a child affected with the disease is increased. Testing of reproductive partners is recommended for carriers of GSD Ib.

GSD I is rare in the general population with an overall incidence of 1:100,000. GSD Ib accounts for about 20% of all GSD I cases.

Genetics Home Reference: Glycogen storage disease type I (http://ghr.nlm.nih.gov/condition/glycogen-storage-disease-type-i)
Association for Glycogen Storage Disease (http://www.agsdus.org/)

OMIM: Glycogen Storage Disease Type Ib (http://www.ncbi.nlm.nih.gov/omim)
Gene Reviews: Glycogen Storage Disease Type I (http://www.ncbi.nlm.nih.gov/books/NBK1116/)

• Full gene sequencing