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

MODY is a monogenic, autosomal dominant form of diabetes mellitus. MODY can be caused by mutations in several genes; glucokinase (GCK) accounts for 30-50% of the cases. The diagnosis can be suspected in early-onset diabetes with atypical features for type 1/type 2. Treatment is usually not recommended. A 5-year-old girl came to our attention for occasional episodes of hyperglycaemia. She was born at term, her birth weight was small for gestational age. At the beginning of her pregnancy, her mother was already on insulin therapy for impaired fasting glucose levels, detected before conception and confirmed in the first weeks of gestation. She was treated with insulin until the childbirth without further investigations. The patient was asymptomatic and in good clinical condition. Basal blood tests have shown a fasting plasma glucose of 125 mg/dl, an HbA1c of 6.5%. Antibodies against islet cells, anti-GAD and anti-ZNT8 antibodies were all negative. A 2-h oral glucose tolerance test was performed and underlined an impaired glucose tolerance. HLA haplotypes were screened, excluding susceptibility. GCK Sanger Sequencing identified a novel heterozygous variant. It is not described as a classical mutations. The analysis has been extended to the parents, finding out the same variant in her mother. To our knowledge this mutation has not been described previously; we believe that this variant is responsible for MODY2 due to FBG and Hb1Ac of all the affected members of family. We suggest high suspicion of an underlying GCK variant in SGA children with hyperglycaemia born to a diabetic mother.

Glucokinase mutations in pediatric patients with impaired fasting glucose

AIMS

Our aim was to detect the frequency of glucokinase (GCK) gene mutations in a cohort of patients with impaired fasting glucose and to describe the clinical manifestations of identified variants. We also aimed at predicting the effect of the novel missense mutations by computational approach.

METHODS

Overall 100 unrelated Italian families with impaired fasting glucose were enrolled and subdivided into two cohorts according to strict and to mild criteria for diagnosis of maturity-onset diabetes of the young (MODY). GCK gene sequencing was performed in all participants.

RESULTS

Fifty-three Italian families with 44 different mutations affecting the GCK and co-segregating with the clinical phenotype of GCK/MODY were identified. All mutations were in heterozygous state. In Sample 1, GCK defects were found in 32/36 (88.9%) subjects selected with strict MODY diagnostic criteria, while in Sample 2 GCK defects were found in 21/64 (32.8%) subjects selected with mild MODY diagnostic criteria.

CONCLUSIONS

Our study enlarged the wide spectrum of GCK defects by adding 9 novel variants. The application of strict recruitment criteria resulted in 88.9% incidence of GCK/MODY, which confirmed it as the commonest form of MODY in the Italian population. In order to avoid misdiagnosis of GCK/MODY, it could be useful to perform molecular screening even if one or more clinical parameters for the diagnosis of MODY are missing. Computational analysis is useful to understand the effect of GCK defect on protein functionality, especially when the novel identified variant is a missense mutation and/or parents' DNA is not available.

A novel hepatocyte nuclear factor-1β (MODY 5) gene mutation in a Romanian boy with pancreatic calcifications, renal and hepatic dysfunction

We report a 12-years-old Romanian boy with a diagnosis of diabetes and renal insufficiency. Mutations in homeodomain-containing transcription factor hepatocyte nuclear factor (HNF-1β) have been reported in association with maturity-onset diabetes of the young (MODY 5) and early maturity-onset diabetes, progressive non-diabetic renal dysfunction and bilateral renal cysts. We found a new heterozygous mutation in HFN-1β located in the exon 3 (c.715 G>C; p.239R) associated to pancreatic calcifications. The importance of molecular diagnosis of MODY patients is reinforced and the need for a careful follow-up is stressed in order to monitor the progression of clinical manifestations and its correlation with the gene mutation.

Estimation of genetic risk for Type 1 diabetes mellitus in newborns on dried blood spot

BACKGROUND

The main contribution to genetic susceptibility for Type 1 Diabetes Mellitus (T1DM) is conferred by the Human Leukocyte Antigens (HLA).

AIM

We evaluated the feasibility of large scale screening on Dried Blood Spot (DBS) to estimate the genetic risk for T1DM in newborns.

SUBJECTS AND METHODS

Peripheral blood DBS samples from 256 newborns, were genotyped for HLA DRB1 and DQB1 alleles identification by a commercially available assay based on a dissociation enhancer lanthanide fluorescence system available in many newborn screening laboratories. Results were compared with those obtained in two wide multicentric studies on cord blood (DIABFIN and PREVEFIN).

RESULTS

Genotyping on DBS revealed 6 subjects at high risk for T1DM, 99 at moderate risk for T1DM and the remaining at low risk for T1DM. We found 100% concordance between both techniques for HLA-DQB1 and DRB1 determination, confirming the feasibility of large scale screening on DBS.

CONCLUSIONS

DBSs represent a resource for future studies about new genetics markers. This assay for estimate the genetic risk of T1DM on DBS showed an excellent sensitivity, specificity and accuracy compared with conventional techniques. Moreover, this assay resulted less expensive, and it could be easily performed on material already collected for newborn screening programs.