tokens: Five novel mutations from Tay - Sachs disease patients were detected a 5 - bp deletion of TCTCC in IVS - 9 ; a 2 - bp deletion of TG in exon 5 ; G78 to A , giving a stop codon in exon 1 ; G533 to T in exon 5 , producing the third amino acid substitution detected at this site ; and G to C at position 1 of IVS - 2 , expected to produce abnormal splicing .