UTP--glucose-1-phosphate uridylyltransferase catalyzing the conversion of glucose-1-phosphate into UDP-glucose, a crucial precursor for the production of glycogen. alpha-D-glucose 1-phosphate + H(+) + UTP = diphosphate + UDP-alpha-D-glucose Glycan biosynthesis; glycogen biosynthesis. Homooctamer. Highly expressed in various brain regions. Expressed in amygdala, anterior cingulate cortex, caudate, cerebellar hemisphere, cerebellum, cortex, frontal cortex, hippocampus, hypothalamus, nucleus accumbens, putamen, spinal cord and substantia nigra (PubMed:31820119). Also widely expressed among other tissues, including liver, heart, placenta, lung, kidney, pancreas and skeletal muscle (PubMed:8354390, PubMed:8631325). Predominantly expressed in developing brain (PubMed:31820119). Preferentially expressed in the developing cortex and cerebellum from gestational weeks 14, 20 and 28 and in the frontal cortex of brains from weeks 21 and 23 (at protein level) (PubMed:31820119). The disease is caused by variants affecting the gene represented in this entry. A recurrent, pathogenic variant affecting the translation initiation codon of isoform 2 has been found in multiple DEE83 families. The variant results in the absence of isoform 2 and leads to reduced levels of functional UGP2 enzyme in neural stem cells. The absence of isoform 2 is compensated by an increased abundance of a functional isoform 1, carrying variant p.Met12Val, which may explain the survival of the patients. A complete absence of functional UGP2 in all cells would be embryonic lethal. Belongs to the UDPGP type 1 family. The human genome was initially thought to contain 2 genes for UTP--glucose-1-phosphate uridylyltransferase: UGP1 and UGP2 (PubMed:8354390, PubMed:8631325). However, the sequence defined as UGP1 (PubMed:8354390) probably does not exist and corresponds to UGP2.