Sanfilippo B syndrome: molecular defects in Greek patients.

Sanfilippo syndrome type B [mucopolysaccharidosis IIIB (MPS IIIB] is the most prevalent type of MPS III in Greece, accounting for 81% of all MPS III cases diagnosed at the Institute of Child Health (Athens) over the last 20 years. The majority of the patients originated from East Central/Central Greece, Thessaly, and Macedonia. We present the results of mutation analysis in 21 Greek patients from 18 different families, all of whom had the severe form of the disorder. Patients were initially screened for five previously known mutations by restriction enzyme digestion of polymerase chain reaction products. Unknown mutations were identified by single-strand conformation polymorphism analysis and DNA sequencing and were confirmed by restriction enzyme analysis. Seven previously described mutations (Y140C, R626X, 503-512del, H414R, G292R, 334del25, and E452K) and four novel mutations (P516L, L242P, E446K, and R482Q) were identified. Expression of the latter and H414R showed that they were all null activity mutations. Considerable genetic heterogeneity has been described in MPS IIIB patients of different origins. In our population, Y140C, H414R, and R626X account for approximately 70% of the studied alleles. Our findings, especially in combination with the origin of individual patients, can improve carrier detection and genetic counseling in affected families.