PI3-kinase mutation linked to insulin and growth factor resistance in vivo

The phosphatidylinositol 3-kinase (PI3K) signaling pathway is central to the action of insulin and many growth factors. Heterozygous mutations in the gene encoding the p85alpha regulatory subunit of PI3K (PIK3R1) have been identified in patients with SHORT syndrome - a disorder characterized by short stature, partial lipodystrophy, and insulin resistance. Here, we evaluated whether SHORT syndrome-associated PIK3R1 mutations account for the pathophysiology that underlies the abnormalities by generating knockin mice that are heterozygous for the Pik3r1Arg649Trp mutation, which is homologous to the mutation found in the majority of affected individuals. Similar to the patients, mutant mice exhibited a reduction in body weight and length, partial lipodystrophy, and systemic insulin resistance. These derangements were associated with a reduced capacity of insulin and other growth factors to activate PI3K in liver, muscle, and fat; marked insulin resistance in liver and fat of mutation-harboring animals; and insulin resistance in vitro in cells derived from these mice. In addition, mutant mice displayed defective insulin secretion and GLP-1 action on islets in vivo and in vitro. These data demonstrate the ability of this heterozygous mutation to alter PI3K activity in vivo and the central role of PI3K in insulin/growth factor action, adipocyte function, and glucose metabolism

Exome Sequencing and Genetic Testing for MODY

Context: Genetic testing for monogenic diabetes is important for patient care. Given the extensive genetic and clinical heterogeneity of diabetes, exome sequencing might provide additional diagnostic potential when standard Sanger sequencing-based diagnostics is inconclusive. Objective: The aim of the study was to examine the performance of exome sequencing for a molecular diagnosis of MODY in patients who have undergone conventional diagnostic sequencing of candidate genes with negative results. Research Design and Methods: We performed exome enrichment followed by high-throughput sequencing in nine patients with suspected MODY. They were Sanger sequencing-negative for mutations in the HNF1A, HNF4A, GCK, HNF1B and INS genes. We excluded common, non-coding and synonymous gene variants, and performed in-depth analysis on filtered sequence variants in a pre-defined set of 111 genes implicated in glucose metabolism. Results: On average, we obtained 45 X median coverage of the entire targeted exome and found 199 rare coding variants per individual. We identified 0–4 rare non-synonymous and nonsense variants per individual in our a priori list of 111 candidate genes. Three of the variants were considered pathogenic (in ABCC8, HNF4A and PPARG, respectively), thus exome sequencing led to a genetic diagnosis in at least three of the nine patients. Approximately 91% of known heterozygous SNPs in the target exomes were detected, but we also found low coverage in some key diabetes genes using our current exome sequencing approach. Novel variants in the genes ARAP1, GLIS3, MADD, NOTCH2 and WFS1 need further investigation to reveal their possible role in diabetes. Conclusion: Our results demonstrate that exome sequencing can improve molecular diagnostics of MODY when used as a complement to Sanger sequencing. However, improvements will be needed, especially concerning coverage, before the full potential of exome sequencing can be realized

A novel GATA6 mutation in a child with congenital heart malformation and neonatal diabetes.

Diabetes in neonates is a monogenetic disease and genetic analysis is warranted to allow best treatment, prognosis, and genetic counseling. Transcription factor mutations may have a variable expression and different organs may be involved

Exome Sequencing and Genetic Testing for MODY

Context: Genetic testing for monogenic diabetes is important for patient care. Given the extensive genetic and clinical heterogeneity of diabetes, exome sequencing might provide additional diagnostic potential when standard Sanger sequencing-based diagnostics is inconclusive.Objective: The aim of the study was to examine the performance of exome sequencing for a molecular diagnosis of MODY in patients who have undergone conventional diagnostic sequencing of candidate genes with negative results.Research Design and Methods: We performed exome enrichment followed by high-throughput sequencing in nine patients with suspected MODY. They were Sanger sequencing-negative for mutations in the HNF1A, HNF4A, GCK, HNF1B and INS genes. We excluded common, non-coding and synonymous gene variants, and performed in-depth analysis on filtered sequence variants in a pre-defined set of 111 genes implicated in glucose metabolism.Results: On average, we obtained 45 X median coverage of the entire targeted exome and found 199 rare coding variants per individual. We identified 0–4 rare non-synonymous and nonsense variants per individual in our a priori list of 111 candidate genes. Three of the variants were considered pathogenic (in ABCC8, HNF4A and PPARG, respectively), thus exome sequencing led to a genetic diagnosis in at least three of the nine patients. Approximately 91% of known heterozygous SNPs in the target exomes were detected, but we also found low coverage in some key diabetes genes using our current exome sequencing approach. Novel variants in the genes ARAP1, GLIS3, MADD, NOTCH2 and WFS1 need further investigation to reveal their possible role in diabetes.Conclusion: Our results demonstrate that exome sequencing can improve molecular diagnostics of MODY when used as a complement to Sanger sequencing. However, improvements will be needed, especially concerning coverage, before the full potential of exome sequencing can be realized.</p

Overall exome coverage and target gene set coverage statistics.

<p>Overall exome coverage and target gene set coverage statistics.</p

Clinical characteristics of the nine MODY probands investigated.

<p>None of the individuals had hearing loss or acantosis nigricans. Data regarding hepatic steatosis, renal cysts, polycystic ovarian disease and triglyceride status were not available in all individuals.</p>a<p>P01 also had partial lipodystrophy with reduced subcutaneous fat in extremities and excess of abdominal subcutaneous fat. There was no evidence of hypertriglyceridemia, hepatic steatosis, acanthosis nigricans or polycystic ovarian disease.</p>b<p>An affected family member was diagnosed at age 28 years.</p><p>Abbreviations: BMI, body mass index; DM, diabetes mellitus; NA, not available; OHA, Oral Hypoglycemic agents; U, international unit (used for insulin doses); y, year; kg, kilo gram body weight.</p

Rare coding variants identified in the 111 target candidate genes using whole exome sequencing in nine patients with suspected MODY.

a<p>SIFT: − tolerated, + not tolerated/PolyPhen-2: − benign, + possibly damaging, ++ probably damaging/Align-GVGD: the Grantham variation (GV), and the Grantham deviation (GD) are combined to provide graded classifiers from most likely to interfere with function (class C65) to least likely (class C0).</p>b<p>Allele frequencies from the interim analysis of phase I of the 1000 Genomes Project, 2010.08.04 sequence index, which included 629 samples (SNPs released in November 2010, indels released in February 2011).</p><p>Abbreviation: Chr, chromosome number; 1000 G, the 1000 Genomes Project; n.a, not analysed due to insufficient number of alignments to make prediction.</p

Partial pedigrees of the nine MODY families investigated.

<p>Squares represent male family members, circles female, and diamonds sex unknown. Numbers inside diamonds show the number of siblings. Black and grey symbols represent persons with diabetes and impaired glucose tolerance, respectively. An arrow denotes the proband in each family and stars indicate those subjects for whom DNA was available. Data under the symbols represent from top to bottom: age at diabetes diagnosis, mutation carrier status (N = Normal allele, M = Mutation), BMI and treatment (INS =  Insulin, OHA = Oral Hypoglycemic Agents).</p

Overview of all substitutions and indels detected in the nine probands before and after variant reduction.

<p>Overview of all substitutions and indels detected in the nine probands before and after variant reduction.</p