Mucopolysaccharidosis (
MPS) IIIB is a lysosomal storage disorder (
LSD) caused by abnormalities of the
enzyme α-N-
acetylglucosaminidase (
NAGLU) that is required for degradation of
heparan sulfate. The patient in this study was a 4-yr-old boy. He presented with normal height and weight,
pectus carinatum, and multiple persistent Mongolian spots on his back. He had mild dysmorphic features with prominent speech developmental delays and, to a lesser extent, motor developmental delays. The
cetylpyridinium chloride precipitation test revealed excessive mucopolysacchariduria (657.2 mg
glycosaminoglycan/g
creatinine; reference range, <175 mg
glycosaminoglycan/g
creatinine). Thin layer chromatography showed urinary
heparan sulfate excretion.
NAGLU enzyme activity was significantly decreased in leukocytes (not detected; reference range, 0.9-1.51 nmol/hr/mg
protein) as well as in plasma (0.14 nmol/hr/mg
protein; reference range, 22.3-60.9 nmol/hr/mg
protein). PCR and direct sequencing analysis of the
NAGLU gene showed that the patient was a compound heterozygote for 2 mutations: c.200T>C (p.L67P) and c.1444C>T (p.R482W). The c.200T>C mutation was a novel finding. This is the first report of a Korean patient with
MPS IIIB who was confirmed by molecular genetic analyses and biochemical investigation.