Significant neuropsychiatric symptoms: three mucopolysaccharidosis type IIIB cases, two of whom were siblings with a novel NAGLU gene mutation.

Mucopolysaccharidosis (MPS) type IIIB patients present with marked neurodevelopmental and neuropsychiatric problems and not with typical MPS symptoms such as coarse facial features, organomegaly, or short body height, especially at the first presentation. We present three pediatric cases, two of which are sisters with novel NAGLU gene mutations, to emphasize that diagnosis of MPS type IIIB should be remembered in patients presenting with neurodevelopmental and neuropsychiatric problems such as delayed speech, autistic-like symptoms, severe behavioral and sleep problems, motor deterioration or idiopathic intellectual disability with or without refractory epilepsy, especially if there is aconsanguineous marriage.