RESUMEN
A major goal of biomedicine is to understand the function of every gene in the human genome. Loss-of-function mutations can disrupt both copies of a given gene in humans and phenotypic analysis of such 'human knockouts' can provide insight into gene function. Consanguineous unions are more likely to result in offspring carrying homozygous loss-of-function mutations. In Pakistan, consanguinity rates are notably high. Here we sequence the protein-coding regions of 10,503 adult participants in the Pakistan Risk of Myocardial Infarction Study (PROMIS), designed to understand the determinants of cardiometabolic diseases in individuals from South Asia. We identified individuals carrying homozygous predicted loss-of-function (pLoF) mutations, and performed phenotypic analysis involving more than 200 biochemical and disease traits. We enumerated 49,138 rare (<1% minor allele frequency) pLoF mutations. These pLoF mutations are estimated to knock out 1,317 genes, each in at least one participant. Homozygosity for pLoF mutations at PLA2G7 was associated with absent enzymatic activity of soluble lipoprotein-associated phospholipase A2; at CYP2F1, with higher plasma interleukin-8 concentrations; at TREH, with lower concentrations of apoB-containing lipoprotein subfractions; at either A3GALT2 or NRG4, with markedly reduced plasma insulin C-peptide concentrations; and at SLC9A3R1, with mediators of calcium and phosphate signalling. Heterozygous deficiency of APOC3 has been shown to protect against coronary heart disease; we identified APOC3 homozygous pLoF carriers in our cohort. We recruited these human knockouts and challenged them with an oral fat load. Compared with family members lacking the mutation, individuals with APOC3 knocked out displayed marked blunting of the usual post-prandial rise in plasma triglycerides. Overall, these observations provide a roadmap for a 'human knockout project', a systematic effort to understand the phenotypic consequences of complete disruption of genes in humans.
Asunto(s)
Consanguinidad , Análisis Mutacional de ADN , Eliminación de Gen , Genes/genética , Estudios de Asociación Genética/métodos , Homocigoto , Fenotipo , 1-Alquil-2-acetilglicerofosfocolina Esterasa/deficiencia , 1-Alquil-2-acetilglicerofosfocolina Esterasa/genética , Apolipoproteína C-III/deficiencia , Apolipoproteína C-III/genética , Estudios de Cohortes , Enfermedad Coronaria/sangre , Enfermedad Coronaria/genética , Familia 2 del Citocromo P450/genética , Grasas de la Dieta/farmacología , Exoma/genética , Ayuno/sangre , Femenino , Frecuencia de los Genes , Humanos , Interleucina-8/sangre , Masculino , Persona de Mediana Edad , Infarto del Miocardio/sangre , Infarto del Miocardio/genética , Neurregulinas/genética , Pakistán , Linaje , Fosfoproteínas/genética , Periodo Posprandial , Sitios de Empalme de ARN/genética , Genética Inversa/métodos , Intercambiadores de Sodio-Hidrógeno/genética , Triglicéridos/sangreRESUMEN
BACKGROUND: Although epidemiological studies have reported positive associations between circulating urate levels and cardiometabolic diseases, causality remains uncertain. OBJECTIVES: Through a Mendelian randomization approach, we assessed whether serum urate levels are causally relevant in type 2 diabetes mellitus (T2DM), coronary heart disease (CHD), ischemic stroke, and heart failure (HF). METHODS: This study investigated 28 single nucleotide polymorphisms known to regulate serum urate levels in association with various vascular and nonvascular risk factors to assess pleiotropy. To limit genetic confounding, 14 single nucleotide polymorphisms exclusively associated with serum urate levels were used in a genetic risk score to assess associations with the following cardiometabolic diseases (cases/controls): T2DM (26,488/83,964), CHD (54,501/68,275), ischemic stroke (14,779/67,312), and HF (4,526/18,400). As a positive control, this study also investigated our genetic instrument in 3,151 gout cases and 68,350 controls. RESULTS: Serum urate levels, increased by 1 SD due to the genetic score, were not associated with T2DM, CHD, ischemic stroke, or HF. These results were in contrast with previous prospective studies that did observe increased risks of these 4 cardiometabolic diseases for an equivalent increase in circulating urate levels. However, a 1 SD increase in serum urate levels due to the genetic score was associated with increased risk of gout (odds ratio: 5.84; 95% confidence interval: 4.56 to 7.49), which was directionally consistent with previous observations. CONCLUSIONS: Evidence from this study does not support a causal role of circulating serum urate levels in T2DM, CHD, ischemic stroke, or HF. Decreasing serum urate levels may not translate into risk reductions for cardiometabolic conditions.
