Figure 3. Genetic analysis of family MEP68. A: AgileMultiIdeogram representation of the homozygous regions from SNP-genotyping data of two affected individuals (IV:1 & IV:3). Homozygous regions are highlighted in light blue, and common autozygous regions are highlighted in dark blue. SIX6 (arrow) maps to a common 42 Mb homozygous region on chromosome 14 (33,856,948–75,827,741, GRCh37, hg19). B: Sequence electropherograms highlighting the nucleotide substitution mutation, c.547G>C, in an affected individual from the family and a normal control subject. C: Multiple protein sequence alignment of human SIX6 with orthologs surrounding the p.D183 residue. Accession numbers: human, NP_031400.2; chimp, XP_522870.3; monkey, XP_014999313.1; dog, XP_547840.3; mouse, NP_035514.1; rat, NP_001101502.1; chicken, NP_001376294; frog, NP_001093696.1; zebrafish NP_957399.1; mosquito, XP_003436640.1. D: Modeling of SIX6 wild-type and p.(Asp183His) mutant. Ribbon representation of the structural model of SIX6 protein (green) bound to DNA (orange). The N-terminus and the atom types at the 183^rd residue (white=carbon; blue=nitrogen; red=oxygen) are highlighted. Note the location of the 183^rd residue sitting in the major groove of double-stranded DNA. It is likely that the change from a negatively charged D183 amino acid in the wild-type sequence to a positively charged H183 in the mutant is likely to disrupt this protein-DNA interaction.