Novel GLIS3 mutations demonstrate an extended multisystem phenotype

INTRODUCTION

Mutations in the GLI-similar 3 (GLIS3) gene encoding the transcription factor GLIS3 are a rare cause of neonatal diabetes and congenital hypothyroidism with six affected cases from three families reported to date. Additional features, described previously, include congenital glaucoma, hepatic fibrosis, polycystic kidneys, developmental delay and facial dysmorphism.

SUBJECTS

We report two new cases from unrelated families with distinct novel homozygous partial GLIS3 deletions. Both patients presented with neonatal diabetes mellitus, severe resistant hypothyroidism in the presence of elevated thyroglobulin and normal thyroid anatomy, degenerative liver disease, cystic renal dysplasia, recurrent infections and facial dysmorphism. These novel mutations have also resulted in osteopenia, bilateral sensorineural deafness and pancreatic exocrine insufficiency, features that have not previously been associated with GLIS3 mutations. Gene dosage analysis showed that the parents were carriers of a deletion encompassing exons 1-2 (case 1) or exons 1-4 (case 2) of the 11 exon gene. Genome-wide SNP analysis did not reveal a common ancestral GLIS3 haplotype in patient 2.

CONCLUSIONS

Our results confirm partial gene deletions as the most common type of GLIS3 mutations, accounting for four of five families identified to date. We propose that mutations in GLIS3 lead to a wider clinical phenotype than previously recognised. We also report the first case of a recessive GLIS3 mutation causing neonatal diabetes and congenital hypothyroidism in a child from a non-consanguineous pedigree, highlighting the importance of molecular genetic testing in any patient with this phenotype.

Mutation surveyor: software for DNA sequence analysis

Advances in high-throughput sequencing techniques had presented a significant challenge to the processing capabilities of genetic laboratories. However, recent developments in the field of semi-automated mutation detection have revolutionised the task of mutation detection.This chapter provides user information for one commercially available program, Mutation Surveyor. The software is manufactured by SoftGenetics (Pennsylvania, USA) and provides an accurate and efficient program for detecting sequence variants. The chapter focuses on the methodology of setting up GenBank files as reference files and provides information on analysis parameters and data processing.

Sequencing of candidate genes selected by beta cell experts in monogenic diabetes of unknown aetiology

CONTEXT

Approximately 39% of cases with permanent neonatal diabetes (PNDM) and about 11% with maturity onset diabetes of the young (MODY) have an unknown genetic aetiology. Many of the known genes causing MODY and PNDM were identified as being critical for beta cell function before their identification as a cause of monogenic diabetes.

OBJECTIVE

We used nominations from the EU beta cell consortium EURODIA project partners to guide gene candidacy.

SUBJECTS

Seventeen cases with permanent neonatal diabetes and 8 cases with maturity onset diabetes of the young.

MAIN OUTCOME MEASURES

The beta cell experts within the EURODIA consortium were asked to nominate 3 "gold", 3 "silver" and 4 "bronze" genes based on biological or genetic grounds. We sequenced twelve candidate genes from the list based on evidence for candidacy.

RESULTS

Sequencing ISL1, LMX1A, MAFA, NGN3, NKX2.2, NKX6.1, PAX4, PAX6, SOX2, SREBF1, SYT9 and UCP2 did not identify any pathogenic mutations.

CONCLUSION

Further work is needed to identify novel causes of permanent neonatal diabetes and maturity onset diabetes of the young utilising genetic approaches as well as further candidate genes.

Wolcott-Rallison syndrome is the most common genetic cause of permanent neonatal diabetes in consanguineous families

CONTEXT AND OBJECTIVE

Mutations in EIF2AK3 cause Wolcott-Rallison syndrome (WRS), a rare recessive disorder characterized by early-onset diabetes, skeletal abnormalities, and liver dysfunction. Although early diagnosis is important for clinical management, genetic testing is generally performed after the full clinical picture develops. We aimed to identify patients with WRS before any other abnormalities apart from diabetes are present and study the overall frequency of WRS among patients with permanent neonatal diabetes.

RESEARCH DESIGN AND METHODS

The coding regions of EIF2AK3 were sequenced in 34 probands with infancy-onset diabetes with a clinical phenotype suggestive of WRS (n = 28) or homozygosity at the WRS locus (n = 6).

RESULTS

Twenty-five probands (73.5%) were homozygous or compound heterozygous for mutations in EIF2AK3. Twenty of the 26 mutations identified were novel. Whereas a diagnosis of WRS was suspected before genetic testing in 22 probands, three patients with apparently isolated diabetes were diagnosed after identifying a large homozygous region encompassing EIF2AK3. In contrast to nonconsanguineous pedigrees, mutations in EIF2AK3 are the most common known genetic cause of diabetes among patients born to consanguineous parents (24 vs. < 2%). Age at diabetes onset and birth weight might be used to prioritize genetic testing in the latter group.

CONCLUSIONS

WRS is the most common cause of permanent neonatal diabetes mellitus in consanguineous pedigrees. In addition to testing patients with a definite clinical diagnosis, EIF2AK3 should be tested in patients with isolated neonatal diabetes diagnosed after 3 wk of age from known consanguineous families, isolated populations, or countries in which inbreeding is frequent.

Clinical heterogeneity in patients with FOXP3 mutations presenting with permanent neonatal diabetes

OBJECTIVE

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is caused by FOXP3 mutations. We aimed to determine the prevalence, genetics, and clinical phenotype of FOXP3 mutations in a large cohort with permanent neonatal diabetes (PNDM).

RESEARCH DESIGN AND METHODS

The 11 coding exons and the polyadenylation region of FOXP3 were sequenced in 26 male subjects with diabetes diagnosed before 6 months of age in whom common genetic causes of PNDM had been excluded. Ten subjects had at least one additional immune-related disorder, and the remaining 16 had isolated diabetes.

RESULTS

We identified four hemizygous FOXP3 mutations in 6 of 10 patients with associated immune-related disorders and in 0 of 16 patients with isolated diabetes (P = 0.002). Three patients with two novel mutations (R337Q and P339A) and the previously reported L76QfsX53 developed classic IPEX syndrome and died within the first 13 months. The novel mutation V408M was found in three patients from two unrelated families and had a mild phenotype with hypothyroidism and autoimmune enteropathy (n = 2) or nephrotic syndrome (n = 1) and survival to 12-15 years.

CONCLUSIONS

FOXP3 mutations result in approximately 4% of cases of male patients with permanent diabetes diagnosed before 6 months. Patients not only have classic IPEX syndrome but, unexpectedly, may have a more benign phenotype. FOXP3 sequencing should be performed in any male patient with the diagnosis of diabetes in the first 6 months who develops other possible autoimmune-associated conditions, even in the absence of full IPEX syndrome.

Hepatocyte nuclear factor-1 beta mutations cause neonatal diabetes and intrauterine growth retardation: support for a critical role of HNF-1beta in human pancreatic development

AIM

The transcription factor hepatocyte nuclear factor-1beta (HNF-1beta) is expressed in rodent pancreatic progenitor cells, where it is an important member of the genetic hierarchy that regulates the generation of pancreatic endocrine and exocrine cells. The recent description of an HNF-1beta mutation in a patient with neonatal diabetes suggests that HNF-1beta may also play a key role in human pancreatic B-cell development. We aimed to investigate the role of HNF-1beta mutations in neonatal diabetes and also the impact of HNF-1beta mutations on fetal growth.

METHODS

We sequenced the HNF-1beta gene in 27 patients with neonatal diabetes in whom other known genetic aetiologies had been excluded. Birth weight was investigated in 21 patients with HNF-1beta mutations.

RESULTS

A heterozygous HNF-1beta mutation, S148L, was identified in one patient with neonatal diabetes diagnosed at 17 days, which rapidly resolved only to relapse at 8 years. This patient had pancreatic atrophy, mild exocrine insufficiency and low birth weight (1.83 kg at 40 weeks' gestation). Intrauterine growth was markedly reduced in patients born to unaffected mothers with a median birth weight of 2.4 kg (range 1.8-3.3) (P = 0.006), median centile weight 3 (0.008-38), and 69% were small for gestational age.

CONCLUSION

HNF-1beta mutations are a rare cause of neonatal diabetes as well as pancreatic exocrine and endocrine dysfunction. Low birth weight is a common feature of patients with HNF-1beta mutations and is consistent with reduced insulin secretion in utero. These findings support a key role for HNF-1beta in early pancreatic progenitor cells in man.

The impact of the angiotensin-converting enzyme insertion/deletion polymorphism on severe hypoglycemia in Type 2 diabetes

The insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme gene (ACE) is associated with altered serum ACE activity. Raised ACE levels and the ACE DD genotype are associated with a 3.2 to 6.8-fold increased risk of severe hypoglycemia in type 1 diabetes. This relationship has not been assessed in type 2 diabetes. We aimed to test for association of the ACE I/D polymorphism with severe hypoglycemia in type 2 diabetes. Patients with type 2 diabetes (n = 308), treated with insulin (n = 124) or sulphonylureas (n = 184), were classified according to whether or not they had previously experienced severe hypoglycemia. Samples of DNA were genotyped for the ACE I/D polymorphism using two alternative polymerase chain reactions to prevent mistyping due to preferential amplification of the D allele. Overall, 12% of patients had previously experienced one or more episodes of severe hypoglycemia. This proportion did not differ between genotype groups (odds ratio (95% confidence limits) for carriers of D allele relative to II homozygotes: 0.79 (0.35-1.78)). This study found no evidence for association of the ACE I/D polymorphism with severe hypoglycemia frequency in patients with type 2 diabetes. However, we cannot rule out a smaller effect (odds ratio </= 1.78). Our results suggest that any effect of ACE genotype on severe hypoglycemia risk in type 2 patients is likely to be smaller than that seen in type 1 diabetes. We recommend future larger-scale studies.

Syndromic obesity and diabetes: changes in body composition with age and mutation analysis of ALMS1 in 12 United Kingdom kindreds with Alstrom syndrome

CONTEXT

Alström syndrome (AS) is a monogenic form of infancy-onset obesity and insulin resistance, caused by ALMS1 mutations. The natural history of the insulin resistance is unknown, in particular how this relates to changes in body composition. It is also unclear how ALMS1 mutations relate to the characteristic phenotype.

OBJECTIVES

Our objectives were to characterize body composition and metabolic parameters, to establish ALMS1 mutation spectrum of United Kingdom AS patients, and to determine whether a genotype-phenotype correlation exists.

DESIGN AND PATIENTS

We conducted a cross-sectional cohort study of 12 unrelated subjects with AS. Age-standardized body composition was assessed by anthropometry and dual-energy x-ray absorptiometry and insulin sensitivity by homeostasis model assessment. The exons and intron-exon boundaries of ALMS1 were directly sequenced.

SETTING

The study was performed during the annual Alström Syndrome UK multidisciplinary screening clinic.

RESULTS

AS patients have early-onset obesity, but body mass index, waist circumference, and body fat from dual-energy x-ray absorptiometry were negatively correlated with age (r = -0.37, P = 0.2; r = -0.84, P = 0.002; and r = -0.6, P = 0.05). Despite this, insulin resistance increased, demonstrated by raised fasting insulin and fall in homeostasis model assessment insulin sensitivity with age (r = -0.64, P = 0.02). ALMS1 mutations were identified in 10 of 12 patients, with a potential founder mutation in exon 16 present in five [np 10775del (C); Del3592fs/ter3597]. No genotype-phenotype correlation was observed.

CONCLUSIONS

We identified mutations in ALMS1 in more than 80% of patients with no genotype-phenotype correlation. In AS, severe childhood obesity, waist circumference, and body fat decrease with age, whereas insulin resistance increases. The abdominal obesity, insulin resistance, diabetes, hypertriglyceridemia, and hypertension suggest that AS could represent a monogenic model for the metabolic syndrome.

Common variations in the ALMS1 gene do not contribute to susceptibility to type 2 diabetes in a large white UK population

AIMS/HYPOTHESIS

Alström syndrome is a rare monogenic disorder characterised by retinal dystrophy, deafness and obesity. Patients also have insulin resistance, central obesity and dyslipidaemia, thus showing similarities with type 2 diabetes. Rare mutations in the ALMS1 gene cause severe gene disruption in Alström patients; however, ALMS1 gene polymorphisms are common in the general population. The aim of our study was to determine whether common variants in ALMS1 contribute to susceptibility to type 2 diabetes in the UK population.

METHODS

Direct sequencing was performed on coding regions and intron/exon boundaries of the ALMS1 gene in 30 unrelated probands with type 2 diabetes. The linkage disequilibrium (LD; D' and r2) and haplotype structure were examined for the identified variants. The common (minor allele frequency [MAF] >5%) single-nucleotide polymorphisms tagging the common haplotypes (tagged SNPs [tSNPs]) were identified and genotyped in 1985 subjects with type 2 diabetes, 2,047 control subjects and 521 families.

RESULTS

We identified 18 variants with MAF between 6 and 38%. Three SNPs efficiently tagged three common haplotypes (rs1881245, rs3820700 and rs1320374). There was no association (all p > 0.05) between the tSNPs and type 2 diabetes in the case-control study and minor alleles of the tSNPs were not overtransmitted to probands with type 2 diabetes in the family study.

CONCLUSIONS/INTERPRETATION

Common variations in the ALMS1 gene were not associated with type 2 diabetes in a large study of a white UK population.

Pharmacological characterisation of a cell line expressing GABA B1b and GABA B2 receptor subunits

The gamma-aminobutyric acid (GABA(B)) receptor has been shown to be a heterodimer consisting of two receptor subunits, GABA(B1) and GABA(B2). We have stably co-expressed these two subunits in a CHO cell line, characterised its pharmacology and compared it to the native receptor in rat brain membranes. Radioligand binding using [3H]CGP54626A demonstrated a similar rank order of potency between recombinant and native receptors: CGP62349>CGP54626A>SCH 50911>3-aminopropylphosphinicacid(3-APPA)>GABA>baclofen>saclofen>phaclofen. However, differences were observed in the affinity of agonists, which were higher at the native receptor, suggesting that in the recombinant system a large number of the receptors were in the low agonist affinity state. In contrast, [35S]GTPgammaS binding studies did not show any differences between recombinant and native receptors with the full agonists GABA and 3-APPA. Measurement of cAMP accumulation in the cells revealed a degree of endogenous coupling of the receptors to G-proteins. This is most likely to be due to the high expression levels of receptors (B(max)=22.5+/-2.5pmol/mg protein) in this experimental system. There was no evidence of GABA(B2) receptors, when expressed alone, binding [3H]CGP54626A, [3H]GABA, [3H]3-APPA nor of GABA having any effect on basal [35S]GTPgammaS binding or cAMP levels.

Association studies of genetic variation in the WFS1 gene and type 2 diabetes in U.K. populations

Mutations in the WFS1 gene cause beta-cell death, resulting in a monogenic form of diabetes known as Wolfram syndrome. The role of variation in WFS1 in type 2 diabetes susceptibility is not known. We sequenced the WFS1 gene in 29 type 2 diabetic probands and identified 12 coding variants. We used 152 parent-offspring trios to look for familial association; the R allele at residue 456 (P = 0.04) and the H allele at residue 611 (P = 0.05) as well as the R456-H611 haplotype (P = 0.032) were overtransmitted to affected offspring from heterozygous parents. In a further cohort of 327 type 2 diabetic subjects and 357 normoglycemic control subjects, the H611 allele and the R456-H611 haplotype were present in more type 2 diabetic subjects than control subjects (one-tailed P = 0.06 and P = 0.023, respectively). In a combined analysis, the H611 allele was present in 60% of all diabetes chromosomes and 55% of all control chromosomes (odds ratio [OR] 1.24 [95% CI 1.03-1.48], P = 0.02), and the R456-H611 haplotype was significantly more frequent in type 2 diabetic subjects than in control subjects (60 vs. 54%, OR 1.29 [95% CI 1.08-1.54], P = 0.0053). Our results provide the first evidence that variation in the WFS1 gene may influence susceptibility to type 2 diabetes.