Analysis of the CYP7A1 gene. (a) DGGE analysis of exon 6 showing the 1302-1303delTT mutation. Prior to DGGE, samples were digested with MboI. Lanes 1, 2, 3, and 5, unaffected individuals; lane 4, subject IV-19. Normal homoduplex bands and mutant, gel-shifted homoduplex band are marked. (b) Sequence of a portion of exon 6 showing the TT deletion, which results in a frameshift and premature stop codon. (c) Diagrammatic depiction of the CYP7A1 gene structure with normal and predicted mutant proteins.