CHARGE syndrome is an autosomal dominant disorder caused in about two-third of cases by mutations in the CHD7 gene. For other genetic diseases e.g. hereditary spastic paraplegia, it was shown that interacting partners are involved in the underlying cause of the disease. These data encouraged us to search for CHD7 binding partners by a yeast two-hybrid library screen and CHD8 was identified as an interacting partner. The result was confirmed by a direct yeast two-hybrid analysis, co-immunoprecipitation studies and by a bimolecular fluorescence complementation assay. To investigate the function of CHD7 missense mutations in the CHD7-CHD8 interacting area on the binding capacity of both proteins, we included three known missense mutations (p.His2096Arg, p.Val2102Ile and p.Gly2108Arg) and one newly identified missense mutation (p.Trp2091Arg) in the CHD7 gene and performed both direct yeast two-hybrid and co-immunoprecipitation studies. In the direct yeast two-hybrid system, the CHD7-CHD8 interaction was disrupted by the missense mutations p.Trp2091Arg, p.His2096Arg and p.Gly2108Arg, whereas in the co-immunoprecipitation studies disruption of the CHD7-CHD8 interaction by the mutations could not be observed. The results lead to the hypothesis that CHD7 and CHD8 proteins are interacting directly and indirectly via additional linker proteins. Disruption of the direct CHD7-CHD8 interaction might change the conformation of a putative large CHD7-CHD8 complex and could be a disease mechanism in CHARGE syndrome.

CHARGE (coloboma, heart defects, atresia of the choanae, retarded growth and development, genital hypoplasia, ear anomalies and deafness) syndrome is a congenital malformation syndrome caused by mutations in the CHD7 gene in approximately 2/3 of cases. In the vast majority of cases, CHARGE syndrome is sporadic. There are only a few reports of parent-to-child transmission and somatic or gonadal mosaicism. To determine the parental origin of CHD7 mutations in sporadic CHARGE syndrome, we screened 30 families for informative exonic or intronic polymorphisms located near the detected CHD7 mutation. An informative polymorphism could be identified in 13 out of 30 families. Linkage analysis was performed between the CHD7 mutation and the polymorphism in the child. In 12 out of 13 families, the mutation affected the paternal allele (92.3%). In our cohort, the mean paternal age at birth was 32.92 years. Comparing the age of fathers of an affected CHARGE patient with the paternal age of the German population in general, we could not observe any paternal age effect. Taken together, we show in this study that de novo CHD7 mutations occur predominantly in the male germ line.

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