Partial ABCC8 gene deletion mutations causing diazoxide-unresponsive hyperinsulinaemic hypoglycaemia

Inactivating mutations in the pancreatic beta cell ATP-sensitive potassium (K(ATP) ) channel genes are identified by sequencing in approximately 80% of patients with diazoxide-unresponsive hyperinsulinaemic hypoglycaemia (HH). Genetic testing is clinically important as the mode of inheritance of a K(ATP) channel mutation(s) provides information on the histological subtype. For example in patients with a single paternally inherited mutation a focal lesion is possible and once confirmed, the patient can undergo a curative lesionectomy. By contrast, recessive inheritance indicates diffuse disease, which requires near-total pancreatectomy, if medical management is unsuccessful. We investigated ABCC8 and KCNJ11 gene dosage in 29 probands from a cohort of 125 with diazoxide-unresponsive HH where sequencing did not provide a genetic diagnosis. We identified heterozygous partial ABCC8 deletions in four probands. In two cases with focal pancreatic disease, a paternally inherited deletion was found. Two other probands with diffuse pancreatic disease were compound heterozygotes for a deletion and a recessively acting mutation that had been identified by sequencing. Family member studies confirmed compound heterozygosity for the deletion and the missense mutation in two affected siblings of one proband. Heterozygous deletions of the ABCC8 gene are a rare, but important cause of diazoxide-unresponsive HH. Dosage analysis should be undertaken in all patients when sequencing analysis does not confirm the genetic diagnosis as confirmation of the mode of inheritance can guide clinical management and will provide important information regarding recurrence risk.

Heterozygous ABCC8 mutations are a cause of MODY

AIMS/HYPOTHESIS

The ABCC8 gene encodes the sulfonylurea receptor 1 (SUR1) subunit of the pancreatic beta cell ATP-sensitive potassium (K(ATP)) channel. Inactivating mutations cause congenital hyperinsulinism (CHI) and activating mutations cause transient neonatal diabetes (TNDM) or permanent neonatal diabetes (PNDM) that can usually be treated with sulfonylureas. Sulfonylurea sensitivity is also a feature of HNF1A and HNF4A MODY, but patients referred for genetic testing with clinical features of these types of diabetes do not always have mutations in the HNF1A/4A genes. Our aim was to establish whether mutations in the ABCC8 gene cause MODY that is responsive to sulfonylurea therapy.

METHODS

We sequenced the ABCC8 gene in 85 patients with a BMI <30 kg/m², no family history of neonatal diabetes and who were deemed sensitive to sulfonylureas by the referring clinician or were sulfonylurea-treated. All had tested negative for mutations in the HNF1A and HNF4A genes.

RESULTS

ABCC8 mutations were found in seven of the 85 (8%) probands. Four patients were heterozygous for previously reported mutations and four novel mutations, E100K, G214R, Q485R and N1245D, were identified. Only four probands fulfilled MODY criteria, with two diagnosed after 25 years and one patient, who had no family history of diabetes, as a result of a proven de novo mutation.

CONCLUSIONS/INTERPRETATION

ABCC8 mutations can cause MODY in patients whose clinical features are similar to those with HNF1A/4A MODY. Therefore, sequencing of ABCC8 in addition to the known MODY genes should be considered if such features are present, to facilitate optimal clinical management of these patients.

Factors associated with upper respiratory tract disease caused by feline herpesvirus, feline calicivirus, Chlamydophila felis and Bordetella bronchiseptica in cats: experience from 218 European catteries

A full history of the management practices and the prevalence of upper respiratory tract disease (URTD) at 218 rescue shelters, breeding establishments and private households with five or more cats was recorded. Oropharyngeal and conjunctival swabs and blood samples were taken from 1748 cats. The prevalences of feline herpesvirus (FHV), feline calicivirus (FCV), Chlamydophila felis and Bordetella bronchiseptica were determined by PCR on swab samples. An ELISA was applied to determine the prevalence of antibodies to B. bronchiseptica. The rates of detection by PCR of each pathogen in the cats in catteries with and without ongoing URTD were, respectively, FHV 16 per cent and 8 per cent; FCV 47 per cent and 29 per cent; C. felis 10 per cent and 3 per cent; and B. bronchiseptica 5 per cent and 1.3 per cent; the seroprevalences of B. bronchiseptica were 61 per cent and 41 per cent, respectively. There was evidence that FHV, FCV and B. bronchiseptica played a role in URTD. The risk factors associated with the disease were less than excellent hygiene, contact with dogs with URTD, and larger numbers of cats in the cattery or household.