Two clinical phenotypes are encountered. The severe neonatal presentation is a rapidly fatal disorder with massive cardiomegaly. The milder variant of the disease is a more slowly progressive muscular disorder.
Enzyme activity is essentially undetectable in both presentations.
Upon cleavage by the enzyme, 4-methylumbelliferone is released and can be quantified fluorimetrically. Turn around time is 3-5 days. Prenatal diagnosis can be performed on cultured amniotic fluid cells or chorionic villus cells. Prior contact with the laboratory is required before submitting any samples for prenatal diagnosis. Turn around time is dependent on cell growth but is usually 1-2 weeks.