Prenatal diagnosis of familial neonatal hyperinsulinemia

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.

Genetic variation in the small heterodimer partner gene and young-onset type 2 diabetes, obesity, and birth weight in U.K. subjects

The orphan receptor small heterodimer partner (SHP, NR0B2) modulates the transcription activity of the MODY1 gene HNF4a. Mutations in SHP were found in 7% of Japanese obese young-onset type 2 diabetic patients and were associated with moderate obesity and increased birth weight. We investigated SHP in 1927 U.K. subjects, examining relationships with type 2 diabetes, obesity, and birth weight. Sequencing of the coding region of SHP in 122 obese, young-onset type 2 diabetic patients detected the polymorphism G171A. The polymorphism was not associated with diabetes in case control or familial association studies. The A allele (frequency 0.07) was not associated with obesity in type 2 diabetic subjects (n = 348), their parents (n = 272), or young nondiabetic adults (n = 925). However, the rare (<1%) AA homozygotes had a raised BMI in each cohort; this was significant when all cohorts were combined (Z score = 0.67 AA vs. -0.05 G/x, P = 0.02). There was no association with corrected birth weight in 382 normal babies, but the only AA baby was 4,069 g. Our study suggests that genetic variation in SHP is unlikely to be common in the predisposition to diabetes, obesity, or increased birth weight in U.K. Caucasians.

Early brain atrophy in persistent hyperinsulinemic hypoglycemia of infancy

We present two siblings with persistent hyperinsulinemic hypoglycemia of infancy, accelerated intrauterine growth and early neonatal brain atrophy. Fetal plasma glucose and insulin levels in the second sibling revealed normoglycemia despite hyperinsulinemia. The absence of intrauterine hypoglycemia suggests that the brain damage is not secondary to hypoglycemia and other etiologies must be considered.

The role of genetic susceptibility in the association of low birth weight with type 2 diabetes

We suggest that altered fetal growth and type 2 diabetes may be two phenotypes of the same genotype - in other words the 'thrifty phenotype' is the result of a 'thrifty genotype'. Supporting this there is strong evidence that paternal factors and, therefore, genes influence fetal growth and that these paternal genes affecting fetal growth may also alter diabetes risk. Further study is needed to determine whether common gene variants can explain the association between reduced birth weight and increased risk of type 2 diabetes. If the genetic hypothesis is true, common diabetes genes are likely to have subtle effects on insulin secretion and/or action and, therefore, subtle effects on fetal growth. Large cohorts of infants and their parents will be required - probably in the region of thousands rather than hundreds - to identify gene variants that may explain the association between reduced birth weight and increased risk of type 2 diabetes. All previously described associations between birth weight and type 2 diabetes have required many hundreds of subjects and it is likely that the geneticists and the 'programmists' are trying to identify very subtle physiological effects.

The fetal insulin hypothesis: an alternative explanation of the association of low birthweight with diabetes and vascular disease

Low birthweight is associated with insulin resistance, hypertension, coronary-artery disease, and non-insulin-dependent diabetes (NIDDM). A suggested explanation for this association is intrauterine programming in response to maternal malnutrition. We propose, however, that genetically determined insulin resistance results in impaired insulin-mediated growth in the fetus as well as insulin resistance in adult life. Low birthweight, measures of insulin resistance in life, and ultimately glucose intolerance, diabetes, and hypertension could all be phenotypes of the same insulin-resistant genotype. There is evidence to support this hypothesis. Insulin secreted by the fetal pancreas in response to maternal glucose concentrations is a key growth factor. Monogenic diseases that impair sensing of glucose, lower insulin secretion, or increase insulin resistance are associated with impaired fetal growth. Polygenic influences resulting in insulin resistance in the normal population are therefore likely to result in lower birthweight. Abnormal vascular development during fetal life and early childhood, as a result of genetic insulin resistance, could also explain the increased risk of hypertension and vascular disease. The predisposition to NIDDM and vascular disease is likely to be the result of both genetic and fetal environmental factors.

[Transitory hyperinsulinism with hypoglycemia in asphyxia neonatorum]

BACKGROUND

Hypoglycemia is a well-known complication in neonates small for gestational age and in those with diabetic mothers. Birth asphyxiated infants can develop severe hypoglycemia due to reduced glycogen stores.

CASE REPORTS

The first patient was born at 41 weeks, weighing 3,780 g by emergency cesarean section because of fetal distress. He developed a pneumothorax and hypoglycemia. He was given glucose infusion (at day 4: 20 mg/kg/d). Hyperinsulinism was confirmed: blood levels at 18.3 mU/L on day 1 and 11.7 mU/L on day 2. The infusion rate was gradually decreased. The second patient was born at 39 weeks, weighing 2,780 g by emergency cesarean section because of fetal distress. She needed glucose infusion (24 g/kg/d) because of hypoglycemia with hyperinsulinism (12.8 mU/L on day 2 and 11.7 mU/L on day 3). After 5 days, the infusion of glucose was replaced by oral feeding only.

CONCLUSION

Transient hypoglycemia in asphyxiated newborn infants with hyperinsulinism must be considered even when hypoglycemia may be difficult to prove.