A novel mutation in GCK gene: Beware of SGA child with diabetic mother

Maternal and Infant Outcomes in GCK-MODY Complicated by Pregnancy

CONTEXT

Challenges exist in the management of Glucokinase-maturity-onset diabetes of the young (GCK-MODY), especially during pregnancy.

OBJECTIVE

This work aimed to evaluate the prevalence of congenital anomaly in newborns from GCK-MODY mothers, and the relationship between fetus genotype and the risk of congenital malformation as well as other adverse pregnancy outcomes.

METHODS

Electronic databases including PubMed, EMBASE, and Cochrane database last updated July 16, 2022, were searched. We included observational studies conducted in GCK-MODY complicated by pregnancy, and reporting at least one pregnancy outcome. We extracted data in duplicate, and the risk of bias was evaluated by the Newcastle-Ottawa Quality Assessment Scale (NOS). All statistical analysis was performed by Cochrane Review Manager.

RESULTS

Eight studies were selected in the meta-analysis. Five were of high quality and 3 were of medium quality evaluated by NOS. A total of 257 GCK-MODY mothers and 499 offspring were enrolled. Among them, 370 offspring were divided into 2 groups: GCK-affected offspring (GCK+, n = 238) and GCK-unaffected offspring (GCK-, n = 132). The percentage of congenital malformations in GCK pregnant women's offspring was 2.4%. The risk of congenital malformations was similar between the GCK+ and GCK- group (odds ratio = 0.56; 95% CI, 0.07-4.51; I2 = 0%; P = .59). The risk of macrosomia/large for gestational age, neonatal hypoglycemia, and combined adverse neonatal outcome was significantly lower in offspring with the GCK mutation compared with non-GCK mutation carriers.

CONCLUSION

The percentage of congenital malformations was 2.4% in GCK-MODY pregnant women's offspring, and newborns with the GCK mutation have lower birth complication than non-GCK mutation carriers.

Pregnancy in Women With Monogenic Diabetes due to Pathogenic Variants of the Glucokinase Gene: Lessons and Challenges

Heterozygous loss-of-function variants of the glucokinase (GCK) gene are responsible for a subtype of maturity-onset diabetes of the young (MODY). GCK-MODY is characterized by a mild hyperglycemia, mainly due to a higher blood glucose threshold for insulin secretion, and an up-regulated glucose counterregulation. GCK-MODY patients are asymptomatic, are not exposed to diabetes long-term complications, and do not require treatment. The diagnosis of GCK-MODY is made on the discovery of hyperglycemia by systematic screening, or by family screening. The situation is peculiar in GCK-MODY women during pregnancy for three reasons: 1. the degree of maternal hyperglycemia is sufficient to induce pregnancy adverse outcomes, as in pregestational or gestational diabetes; 2. the probability that a fetus inherits the maternal mutation is 50% and; 3. fetal insulin secretion is a major stimulus of fetal growth. Consequently, when the fetus has not inherited the maternal mutation, maternal hyperglycemia will trigger increased fetal insulin secretion and growth, with a high risk of macrosomia. By contrast, when the fetus has inherited the maternal mutation, its insulin secretion is set at the same threshold as the mother's, and no fetal growth excess will occur. Thus, treatment of maternal hyperglycemia is necessary only in the former situation, and will lead to a risk of fetal growth restriction in the latter. It has been recommended that the management of diabetes in GCK-MODY pregnant women should be guided by assessment of fetal growth by serial ultrasounds, and institution of insulin therapy when the abdominal circumference is ≥ 75th percentile, considered as a surrogate for the fetal genotype. This strategy has not been validated in women with in GCK-MODY. Recently, the feasibility of non-invasive fetal genotyping has been demonstrated, that will improve the care of these women. Several challenges persist, including the identification of women with GCK-MODY before or early in pregnancy, and the modalities of insulin therapy. Yet, retrospective observational studies have shown that fetal genotype, not maternal treatment with insulin, is the main determinant of fetal growth and of the risk of macrosomia. Thus, further studies are needed to specify the management of GCK-MODY pregnant women during pregnancy.