The strongest signal for Conscientiousness was with a SNP within the gene SMOC1 (rs11626232; P = 4.82 × 10−6), which also showed a meta-analytic trend in the replication samples (P = .11). Conscientiousness was strongly associated with rs2835731 (P = 2.81 × 10−5) and other SNPs within the gene DYRK1A, which is thought to have an effect on brain development. However, the association was not supported in the follow-up samples. DYRK1A maps to the Down Syndrome critical region on chromosome 21, and several other lines of evidence, including observations in a transgenic mouse model (82), suggest that DYRK1A is involved in mental retardation associated with Down Syndrome (83). Furthermore, DYRK1A has been associated with Alzheimer disease (84). Being persistent, organized, and self-controlled are central traits of Conscientiousness, and deficiencies along these dimensions are clinical features associated with the neurodegenerative diseases for which DYRK1A has been implicated. There are several studies that support the links of Conscientiousness with Alzheimer disease (85, 86).
