Non-familial cohort
When large families with the disease are not readily available, one could perform WES on a number of unrelated patients with similar clinical manifestations and select genes that are commonly mutated in the patient cohort. In carrying out such an experiment, it is important to consider the background mutation burden of the entire human gene set; it is possible that the longest genes might contain the highest number of rare functional variants and therefore appear to be the most interesting. To circumvent such errors in analysis, the variant burden of each gene should be normalized using data from a control population. In a WES study of pseudohypoaldosteronism type II (PHAII), the variant burden of every gene from 11 unrelated patients was compared against that of 699 controls [7]. A single gene that was specifically enriched for mutations in the patient set, KLHL3, was identified (5 variants from 11 patients compared to 2 from 699 controls, with p-value of 1.1 × 10-8).