A de novo paradigm for mental retardation

Joris Veltman, Han Brunner and colleagues report results of a family based exome sequencing study of ten individuals with unexplained mental retardation. They identified and validated de novo mutations in nine genes, six of which are likely to be pathogenic based on functional criteria, suggesting an important role for de novo point mutations in the etiology of unexplained mental retardation. The per-generation mutation rate in humans is high. De novo mutations may compensate for allele loss due to severely reduced fecundity in common neurodevelopmental and psychiatric diseases, explaining a major paradox in evolutionary genetic theory. Here we used a family based exome sequencing approach to test this de novo mutation hypothesis in ten individuals with unexplained mental retardation. We identified and validated unique non-synonymous de novo mutations in nine genes. Six of these, identified in six different individuals, are likely to be pathogenic based on gene function, evolutionary conservation and mutation impact. Our findings provide strong experimental support for a de novo paradigm for mental retardation. Together with de novo copy number variation, de novo point mutations of large effect could explain the majority of all mental retardation cases in the population.