Genome-wide association identifies nine common variants associated with fasting proinsulin levels and provides new insights into the pathophysiology of type 2 diabetes

OBJECTIVE

Proinsulin is a precursor of mature insulin and C-peptide. Higher circulating proinsulin levels are associated with impaired β-cell function, raised glucose levels, insulin resistance, and type 2 diabetes (T2D). Studies of the insulin processing pathway could provide new insights about T2D pathophysiology.

RESEARCH DESIGN AND METHODS

We have conducted a meta-analysis of genome-wide association tests of ∼2.5 million genotyped or imputed single nucleotide polymorphisms (SNPs) and fasting proinsulin levels in 10,701 nondiabetic adults of European ancestry, with follow-up of 23 loci in up to 16,378 individuals, using additive genetic models adjusted for age, sex, fasting insulin, and study-specific covariates.

RESULTS

Nine SNPs at eight loci were associated with proinsulin levels (P < 5 × 10(-8)). Two loci (LARP6 and SGSM2) have not been previously related to metabolic traits, one (MADD) has been associated with fasting glucose, one (PCSK1) has been implicated in obesity, and four (TCF7L2, SLC30A8, VPS13C/C2CD4A/B, and ARAP1, formerly CENTD2) increase T2D risk. The proinsulin-raising allele of ARAP1 was associated with a lower fasting glucose (P = 1.7 × 10(-4)), improved β-cell function (P = 1.1 × 10(-5)), and lower risk of T2D (odds ratio 0.88; P = 7.8 × 10(-6)). Notably, PCSK1 encodes the protein prohormone convertase 1/3, the first enzyme in the insulin processing pathway. A genotype score composed of the nine proinsulin-raising alleles was not associated with coronary disease in two large case-control datasets.

CONCLUSIONS

We have identified nine genetic variants associated with fasting proinsulin. Our findings illuminate the biology underlying glucose homeostasis and T2D development in humans and argue against a direct role of proinsulin in coronary artery disease pathogenesis.

Cardiovascular health of Finnish war evacuees 60 years later

BACKGROUND

Early life experiences might have long-term effects on health.

AIM

To assess prevalence of cardiovascular disease and diabetes in later life among individuals exposed to traumatic separation in early childhood due to World War II.

METHODS

Of the participants of the Helsinki Birth Cohort 1934-44 Study (n=2003), 320 had been evacuated abroad to temporary foster care in childhood. The remaining participants served as controls. The mean age at evacuation was 4.8 (SD=2.4) years and the mean duration of the evacuation was 1.7 (SD=1.0) years.

RESULTS

Cardiovascular morbidity was higher among the former war evacuees (14.7% versus 7.9%; odds ratio (OR)=2.0, 95% confidence interval (95% CI) 1.4-2.9; P<0.001). A similar difference in prevalence of type 2 diabetes was observed (19.7% versus 14.8%; OR=1.4, 95% CI 1.1-1.9, P=0.025). The former war evacuees were also more likely to be hypertensive (P<0.05). The effects on morbidity were not explained by age at testing or socio-economic circumstances in childhood or adulthood.

CONCLUSION

Early life traumatic events may extend lifelong effects on health. This study is among the first to show that early life trauma predicts higher prevalence of cardiovascular disease and type 2 diabetes in late adulthood, in a longitudinal clinical study setting.

A possible link between the pubertal growth of girls and breast cancer in their daughters

One hypothesis for the origins of breast cancer is that it is initiated by exposure of developing breast tissue in utero to maternal sex hormones. The sex hormone profile is established at puberty, when it regulates growth of the pelvic bones. The pubertal growth of girls is characterized by broadening and rounding of the pelvis. The maximal width between their iliac crests, the intercristal width, increases more rapidly than in boys. We hypothesized that higher sex hormone concentrations at puberty produce larger intercristal widths, and these are markers of increased breast cancer risk in the next generation. We followed up 6,370 women who were born in Helsinki during 1934-1944, and whose mothers' pelvic bones were measured during routine antenatal care. Women whose mothers had large intercristal widths had higher rates of breast cancer. In those born at or after 40 weeks gestation, the hazard ratio for breast cancer was 3.7 (95% CI: 2.1-6.6) if their mother's intercristal width was greater than 30 cm. Among women born to multiparous mothers this hazard ratio rose to 7.2 (3.4-15.4). Hazard ratios for breast cancer were also higher in the daughters of mothers with round iliac crests. Pelvic bone measurements which increase similarly in girls and boys at puberty did not predict breast cancer. We conclude that the intercristal width, and the roundness of the iliac crests, are markers of mothers' sex hormones, and postulate that high concentrations cause genetic instability in differentiating breast cells in their daughters in utero.

Maternal and Social Origins of Hypertension

We previously reported that in 2003 people from the Helsinki birth cohort whose blood pressures were measured, 2 different paths of growth preceded the development of hypertension. People already diagnosed with hypertension were small at birth but of average body size at age 11 years. People newly diagnosed with hypertension grew slowly in utero and through childhood. We have now examined how the mother’s body size, placental size, and living conditions after birth, 3 influences that affect growth, affect hypertension. Diagnosed hypertension was associated with low placental weight and poor living conditions after birth. The odds ratios were 1.6 (95% CI, 1.1 to 2.3) in people with placental weights <550 g, compared with those with weights >750 g, and 2.2 (95% CI, 1.5 to 3.3) in people whose fathers were laborers compared with those in upper middle-class families. Newly diagnosed hypertension was associated with a small anteroposterior diameter of the mother’s bony pelvis, a known consequence of rickets or lesser degrees of malnutrition in infancy. The odds ratio was 2.2 (95% CI, 1.4 to 3.5) in people whose mothers’ pelvic external conjugate diameters were <18 cm when compared with people whose mothers’ diameters were ≥19 cm. We conclude that one path of growth that leads to hypertension is initiated by fetal undernutrition, which may make a baby vulnerable to postnatal stress, whereas the other originates in a functional incapacity in the mother’s metabolism, possibly protein metabolism, which she acquired through undernutrition during her infancy.

Pathways of infant and childhood growth that lead to type 2 diabetes

OBJECTIVE

Although a link between small body size at birth and later type 2 diabetes has been repeatedly documented, less is known about the associations between the disease and growth during infancy. The aim of this study was to explore the pathways of infant and early growth that lead to type 2 diabetes in adult life.

RESEARCH DESIGN AND METHODS

We carried out a longitudinal study of 8760 subjects born in Helsinki from 1934 to 1944. On average, they had 8 measurements of height and weight between birth and 1 year of age and another 10 measurements between 1 and 12 years of age. We identified people with type 2 diabetes using a national register.

RESULTS

Among babies whose birth weights were <or=3.5 kg, the rate of infant growth was unrelated to later type 2 diabetes. Among babies with birth weights >3.5 kg, slow growth in length between birth and 3 months of age predicted later disease. Rapid gain in BMI after age 2 years increased the risk of later disease in both groups of babies, but this effect was greatest among children who had slow growth in length between birth and 3 months of age. In children whose Z-scores for length decreased, an SD increase in BMI at age 12 years was associated with an odds ratio (OR) for type 2 diabetes of 1.77 (95% CI 1.50-2.09). The corresponding OR in subjects whose Z-scores for length increased was 1.42 (95% CI 1.20-1.69). Rapid gain in childhood BMI was associated with high maternal BMI and socioeconomic factors (fewer people in the home and lower social class).

CONCLUSIONS

Babies with above-average birth weights may develop type 2 diabetes later in life if poor living conditions lead to faltering growth in length in the first few months after birth. We speculate that growth faltering at this time is associated with lifelong impairment of insulin metabolism and inability to meet the challenge of rapid childhood increase in BMI.