Mutation screening of the entire coding regions of the TSC1 and the TSC2 gene with the protein truncation test PTT identifies frequent splicing defects

Mutation analyses in tuberous sclerosis (TSC) have reported a wide variety of disease-causing aberrations in the two known predisposing genes, TSC1 an d TSC2 on chromosomes 9q34 and 16p13, comprising mainly small mutations dis tributed over the entire genes. So far, all known TSC1 mutations as well as the majority of TSC2 mutations truncate the proteins hamartin and tuberin, respectively. We describe for the first time an RNA-based screening of the entire coding regions of both TSC genes for truncating mutations applying the protein truncation test (PTT). Simultaneous investigation of both TSC g enes in a group of 48 unassigned TSC patients, which were previously tested to exclude large intragenic TSC2 rearrangements, revealed aberrant migrati ng polypeptides resulting from truncating mutations in nine TSC1 cases and in 16 TSC2 eases while three TSC2 cases showed enlarged proteins. TSC1 muta tions include two nonsense mutations, four insertions, and three splice mut ations. Nineteen mutations identified in TSC2 were composed of four differe nt nonsense mutations in five patients, one deletion, one insertion, and se ven different splicing aberrations due to at least eight different mutation s found in 12 patients. Additional predicted truncating mutations according to PTT without possible identification of the causative alteration allowed assignment to TSC1 in one and TSC2 in seven cases. Twelve patients without abnormalities in the PTT are assumed to harbor missense mutations, probabl y in TSC2. The high proportion of TSC2 splicing aberrations strengthens the importance of intronic disease causing mutations and the application of RN A-based screening methods to confirm their consequences. Hum Mutat 14:401-4 11, 1999, (C) 1999 Wiley-Liss, Inc.