Mutations in the GALT gene encoding Galactose-1-phosphate uridylyl transferase are the most common cause of galactosemia, an autosomal recessive inborn error of metabolism. The cardinal features of classic galactosemia are hepatomegaly, cataracts, and mental retardation. Failure to thrive is the most common initial clinical symptom of galactosemia. Children with galactosemia require a special diet. Most cases of galactosemia are caused by sequence variants; however, occasionally there are deletions involving all or part of the GALT gene. This laboratory performs both Sanger sequencing of the GALT gene and deletion/duplication by MLPA.