Congenital Disorders of Glycosylation (CDG) are a heterogenous group of primarily autosomal recessive mendelian diseases caused by disruptions in the synthesis of lipid linked oligosaccha-rides and their transfer to proteins. CDGs affect multiple organ systems and vary in presentation, even within families. Here we describe a chemically induced mouse mutant, tvrm76, with early onset photoreceptor degeneration. The recessive mutation was mapped to Chromosome 9 and as-sociated with a missense mutation in the Dpagt1 gene encoding UDP-N-acetyl-D-glucosamine:dolichyl-phosphate N-acetyl-D-glucosaminephosphotransferase (EC 2.7.8.15). The mutation is predicted to cause a substitution of aspartic acid with glycine at residue 166 of DPAGT1. Increased expression of Ddit3, and elevated levels of HSPA5 (BiP) sug-gest the presence of early-onset endoplasmic reticulum (ER) stress. These changes were associated with induction of photoreceptor apoptosis in tvrm76 retinas. Mutations in human DPAGT1 cause Myasthenic Syndrome 13 and severe forms of Congenital Disorder of Glycosylation Type Ij. In contrast, Dpagt1tvrm76 homozygous mice present with congenital photoreceptor degeneration without overt muscle or muscular junction involvement. Our results suggest the possibility of DPAGT1 mutations in human patients that present primarily with retinitis pigmentosa with little or no muscle disease. Variants in DPAGT1 should be considered when evaluating cases of non-syndromic retinal degeneration.