Offspring birthweight is not associated with paternal insulin resistance

Two decades since the fetal insulin hypothesis: what have we learned from genetics?

In 1998 the fetal insulin hypothesis proposed that lower birthweight and adult-onset type 2 diabetes are two phenotypes of the same genotype. Since then, advances in research investigating the role of genetics affecting insulin secretion and action have furthered knowledge of fetal insulin-mediated growth and the biology of type 2 diabetes. In this review, we discuss the historical research context from which the fetal insulin hypothesis originated and consider the position of the hypothesis in light of recent evidence. In summary, there is now ample evidence to support the idea that variants of certain genes which result in impaired pancreatic beta cell function and reduced insulin secretion contribute to both lower birthweight and higher type 2 diabetes risk in later life when inherited by the fetus. There is also evidence to support genetic links between type 2 diabetes secondary to reduced insulin action and lower birthweight but this applies only to loci implicated in body fat distribution and not those influencing insulin resistance via obesity or lipid metabolism by the liver. Finally, we also consider how advances in genetics are being used to explore alternative hypotheses, namely the role of the maternal intrauterine environment, in the relationship between lower birthweight and adult cardiometabolic disease.

Reduced Birth Weight, Decreased Early-Phase Insulin Secretion, and Increased Glucose Concentrations after Oral Glucose Tolerance Test in Japanese Women Aged 20 Years with Family History of Type 2 Diabetes

INTRODUCTION

We tested the hypothesis that family history of type 2 diabetes (FHD) is associated with reduced birth weight and reduced insulin secretion later in life.

MATERIALS AND METHODS

Birth weight, body composition by whole-body dual-energy X-ray absorptiometry, and homeostasis model assessment-insulin resistance were compared between Japanese women aged 20 years with positive (n = 73) and negative (n = 258) FHD. A subsample of 153 women (57 with positive FHD) underwent a 75 g oral glucose tolerance test. Multivariate logistic regression analyses were used to identify the most important determinants of FHD.

RESULTS

Women with positive as compared with negative FHD had lower birth weight (3132 ± 364 vs. 3238 ± 418 g, p = 0.04). However, the current fat mass index and trunk/leg fat ratio, sophisticated measures of general and abdominal fat accumulation, respectively, did not differ. Women with positive FHD had a lower insulinogenic index (2.4 ± 7.3 vs. 6.2 ± 16, p = 0.007) and higher area under the glucose curve (217 ± 47 vs. 198 ± 36 mg/dL/2 h, p = 0.006). However, fasting and postload insulinemia, homeostasis model assessment-insulin resistance, and Matsuda index did not differ. In multivariate logistic regression analysis, birth weight was marginally associated with FHD (odds ratio, 0.999; 95% confidential interval, 0.98-1.00000; p = 0.0509).

CONCLUSIONS

FHD was associated not only with reduced birth weight but also with decreased early-phase insulin secretion and increased postload glucose concentrations in Japanese women aged 20 years. These findings may be in keeping with the fetal insulin hypothesis and provide some evidence that FHD can alter size at birth, probably through genetic and shared environmental components, which consequently resulted in decreased early-phase insulin secretion and increased glucose excursion in the early twenties. FHD was not related to sophisticated measures of general and abdominal adiposity and insulin resistance/sensitivity.

Genetic influences on the association between fetal growth and susceptibility to type 2 diabetes

The fetal insulin hypothesis proposes that low birth weight and susceptibility to type 2 diabetes (T2D) could both be two phenotypes of the same genotype. Insulin is a key growth factor in utero, and T2D is characterized by insulin resistance and/or beta-cell dysfunction. Therefore, genetic variants impacting on insulin secretion and action are likely to alter both fetal growth and susceptibility to T2D. There are three lines of evidence in support of this hypothesis. (1) Studies of rare monogenic diabetes have shown mutations in a single gene, such as GCK or KCNJ11, can cause diabetes by reducing insulin secretion, and these mutations are also associated with reduced birth weight. (2) Epidemiological studies have indicated that children born to fathers with diabetes are born smaller. As the father cannot influence the intrauterine environment, this association is likely to reflect genes inherited by the fetus from the father. (3) The most compelling evidence comes from recent genome-wide association studies. Variants in the CDKAL1 and HHEX-IDE genes that predispose to diabetes, if present in the fetus, are associated with reduced birth weight. These data provide evidence for a genetic contribution to the association between low birth weight and susceptibility to T2D. This genetic background is important to take into consideration when investigating the impact of environmental determinants and developing strategies for intervention and prevention.

High-fat diet aggravates glucose homeostasis disorder caused by chronic exposure to bisphenol A

Epidemiological findings on the association between bisphenol A (BPA, 2,2-bis-(4-hydroxyphenyl)propane) exposure and type 2 diabetes mellitus (T2DM) are paradoxical. In animal studies, BPA has been shown to disrupt pancreatic function and blood glucose homeostasis even at a reference 'safe' level during perinatal period. In this study, we explored the effects of long-term paternal exposure to a 'safe' level of BPA on parents themselves and their offspring. Adult male genitor rats fed with either standard chow diet (STD) or high-fat diet (HFD) were treated respectively with either vehicle or BPA (50 μg/kg per day) for 35 weeks. The male rats treated with vehicle or BPA for 21 weeks were then used as sires, and the adult female rats were fed with STD during the gestation and lactation. Offspring rats were weaned on postnatal day 21 and fed with STD in later life. Metabolic parameters were recorded on the adult male rats and their adult offspring. BPA exposure disrupted glucose homeostasis and pancreatic function, and HFD aggravated these adverse effects. However, BPA exposure did not alter body weight, body fat percentage, or serum lipid. In addition, the paternal BPA exposure did not cause adverse reproductive consequence or metabolic disorder in the adult offspring. Our findings indicate that chronic exposure to a predicted 'safe' dose of BPA contributes to glucose metabolic disorders, and that HFD aggravates these adverse effects in paternal rats.

Paternal metabolic and cardiovascular risk factors for fetal growth restriction: a case-control study

OBJECTIVE

Fathers of low-birth weight offspring are more likely to have type 2 diabetes and cardiovascular disease in later life. We investigated whether paternal insulin resistance and cardiovascular risk factors were evident at the time that fetal growth-restricted offspring were born.

RESEARCH DESIGN AND METHODS

We carried out a case-control study of men who fathered pregnancies affected by fetal growth restriction, in the absence of recognized fetal disease (n = 42), compared with men who fathered normal-birth weight offspring (n = 77). All mothers were healthy, nonsmoking, and similar in age, BMI, ethnicity, and parity. Within 4 weeks of offspring birth, all fathers had measures of insulin resistance (HOMA index), blood pressure, waist circumference, endothelial function (flow-mediated dilatation), lipid profile, weight, and smoking habit. Comparison was made using multivariable logistical regression analysis.

RESULTS

Fathers of fetal growth-restricted offspring [mean (SD) 1.8th (2.2) customized birth centile] were more likely to have insulin resistance, hypertension, central adiposity, and endothelial dysfunction and to smoke cigarettes compared with fathers of normal grown offspring. After multivariable analysis, paternal insulin resistance and smoking remained different between the groups. Compared with fathers of normal grown offspring, men who fathered pregnancies affected by fetal growth restriction had an OR 7.68 (95% CI 2.63-22.40; P < 0.0001) of having a 1-unit higher log HOMA-IR value and 3.39 (1.26-9.16; P = 0.016) of being a smoker.

CONCLUSIONS

Men who recently fathered growth-restricted offspring have preclinical evidence of the insulin resistance syndrome and are more likely to smoke than fathers of normal grown offspring. Paternal lifestyle may influence heritable factors important for fetal growth.

Offspring birth weight and cardiovascular risk in parents: a population-based HUNT 2 study

Low birth weight is associated with increased risk of cardiovascular disease and type 2 diabetes in later life. The fetal insulin hypothesis suggests that shared genetic factors partly explain this association. If fetal genes predispose to both low birth weight and cardiovascular disease in adulthood, fathers of offspring with low birth weight should display an unfavorable profile of cardiovascular risk factors. To study this, the authors linked data on more than 14,000 parents, collected from the second Health Study of Nord Trøndelag County, Norway (HUNT 2, 1995-1997), to offspring data from the Norwegian Medical Birth Registry (1967-2005). Linear regression was used to study associations of offspring birth weight for gestational age with the parents' body mass index, waist circumference, blood pressure, glucose, and serum lipids. All analyses were adjusted for shared environment by means of the socioeconomic measures, lifestyle, and cardiovascular risk factors of the partner. The authors found that low offspring birth weight for gestational age was associated with increased paternal blood pressure, body mass index, waist circumference, and unfavorable levels of glucose and lipids. For mothers, associations similar to those for fathers were found for blood pressure, whereas associations in the opposite direction were found for glucose, lipids, and body mass index. The paternal findings strengthen the genetic hypothesis.

Familial (shared environmental and genetic) factors and the foetal origins of cardiovascular diseases and type 2 diabetes: a review of the literature

Several researchers have argued that observed associations between birth weight and cardiovascular diseases, and type 2 diabetes, may be confounded by familial (shared environmental and genetic) factors. However, most studies have found that shared environmental factors, including socio-economic factors, do not influence the foetal origins of adult diseases. Results from two twin studies suggest that genetic factors may be of importance for the association between birth weight and risks of coronary heart disease, but findings from intergenerational studies are not consistent with genetic confounding. More studies have assessed the importance of genetic factors with respect to risk factors of coronary heart, including raised blood pressure and lipid levels. Recent findings suggest that the association between birth weight and hypertension is independent of genetic factors. In contrast, recent twin and intergenerational studies favour the hypothesis that the association between birth weight and risk of type 2 diabetes is confounded by genetic factors.

Importance of familial factors in associations between offspring birth weight and parental risk of type-2 diabetes

BACKGROUND

It is hypothesized that associations found between birth weight and subsequent risk of type-2 diabetes are due to inherited genes affecting both fetal growth and metabolism of insulin.

METHODS

To study whether there is a familial (shared environmental and genetic) link between birth weight and type-2 diabetes, the authors used a sample of 11,411 Swedish like-sexed twins born from 1926 to 1958 with at least one offspring, to study the association between offspring birth weight for gestational age and parental risk of type-2 diabetes.

RESULTS

Decreasing offspring birth weight for gestational age (with 1 SD) was associated with an increased risk of type-2 diabetes among father's [odds ratio (OR)=1.72, 95% confidence interval (CI): 1.33-2.23] and decreased risk among mothers (OR=0.43, 95% CI: 0.30-0.62), independent of grand parental and parental socio-economic status and parental smoking. In paired twin analysis, the association between offspring birth weight and mothers with risk of type-2 diabetes was similar within- and between-twin pairs, whereas father's risk was slightly smaller within than between pairs (OR(Between)=1.90, 95% CI: 1.10-3.28, and OR(Within)=1.71, 95% CI: 1.10-2.67, respectively).

CONCLUSIONS

The well-established association between paternal type-2 diabetes and offspring birth weight seems to primarily be due to as yet unidentified non-shared environmental factors. However, familial factors shared within twin pairs may contribute to the association.