Required for normal glycogen accumulation (PubMed:8463281, PubMed:26199317, PubMed:8613547). The alpha 1-6 branches of glycogen play an important role in increasing the solubility of the molecule (Probable). Transfers a segment of a (1->4)-alpha-D-glucan chain to a primary hydroxy group in a similar glucan chain. Glycan biosynthesis; glycogen biosynthesis. Monomer. Binds its carbohydrate substrate close to the active site, but also via regions close to the N-terminus; this may result in increased affinity and therefore increased catalytic efficiency. The disease is caused by variants affecting the gene represented in this entry. Neuromuscular perinatal glycogen storage disease type 4 is associated with non-immune hydrops fetalis, a generalized edema of the fetus with fluid accumulation in the body cavities due to non-immune causes. Non-immune hydrops fetalis is not a diagnosis in itself but a symptom, a feature of many genetic disorders, and the end-stage of a wide variety of disorders. The disease is caused by variants affecting the gene represented in this entry. Belongs to the glycosyl hydrolase 13 family. GlgB subfamily.