Enables (N-acetylneuraminyl)-galactosylglucosylceramide N-acetylgalactosaminyltransferase activity. Involved in ganglioside biosynthetic process. Located in Golgi membrane and plasma membrane. Human ortholog(s) of this gene implicated in hereditary spastic paraplegia 26. Orthologous to human B4GALNT1 (beta-1,4-N-acetyl-galactosaminyltransferase 1). [provided by Alliance of Genome Resources, Apr 2022]