Background. Natural selection operates on genetically influenced phenotypic variations that confer differential survival or reproductive advantages. Common diseases are frequently associated with increased mortality and disability and complex heritable factors play an important role in their pathogenesis. Hence, common diseases should trigger the process of natural selection with subsequent population genetic response. However, empirical impact of natural selection on genetics of complex diseases is poorly understood. In this paper, I hypothesize that negative selection of diseased individuals leads to systemic genetic differences between common diseases that primarily occur before or during the reproductive years (early onset) and those that occur after the reproductive years (late onset).
Methods. To test this hypothesis, a comprehensive literature survey of highly penetrant (80% or more) nonpleiotropic, nonsyndromic susceptibility genes (hereafter defined as Mendelian phenocopies) was completed for early versus late onset common diseases, organized using the World Health Organization (WHO) ICD-10 classification scheme. An average age at sporadic disease onset of 30 years was selected for dividing early versus late onset common diseases.
Results. Mendelian phenocopies were identified for 16 primarily late onset common diseases from 9 distinct WHO diagnostic categories. Late onset common diseases with Mendelian phenocopies include papillary renal carcinoma, obesity, Alzheimer disease, Parkinson disease, frontotemporal dementia, amyotrophic lateral sclerosis, primary open angle glaucoma, age-related hearing loss, coronary artery disease, stroke, pancreatitis, thrombotic thrombocytopenic purpura, systemic lupus erythematosus, inclusion body myositis, Paget's disease of bone and focal segmental glomerulosclerosis (steroid resistant). In contrast, no Mendelian phenocopy was found for any primarily early onset common disease (p<5.8x10-4). Thus, highly predictive rare variants are present for a subset of late onset common diseases, but not for early onset common diseases.
Discussion. These findings suggest that genetic architecture of early onset common diseases is more robust against the phenotypic expression of highly penetrant predisposing mutations than is the case for late onset common diseases. The primary candidate for increased genetic robustness in early onset common diseases is proposed to be natural selection.
Natural Selection at the NHLH2 Core Promoter Exceptionally Long CA-Repeat in Human and Disease-Only Genotypes in Late-Onset Neurocognitive Disorder
