A nonsense loss-of-function mutation in PCSK1 contributes to dominantly inherited human obesity

BACKGROUND

A significant proportion of severe familial forms of obesity remain genetically elusive. Taking advantage of our unique cohort of multigenerational obese families, we aimed to assess the contribution of rare mutations in 29 common obesity-associated genes to familial obesity, and to evaluate in these families the putative presence of nine known monogenic forms of obesity.

METHODS

Through next-generation sequencing, we sequenced the coding regions of 34 genes involved in polygenic and/or monogenic forms of obesity in 201 participants (75 normal weight individuals, 54 overweight individuals and 72 individuals with obesity class I, II or III) from 13 French families. In vitro functional analyses were performed to investigate the mutation PCSK1-p.Arg80* which was identified in a family.

RESULTS

A novel heterozygous nonsense variant in PCSK1 (p.Arg80*), encoding a propeptide truncated to less than two exons (out of 14), was found to co-segregate with obesity in a three-generation family. We demonstrated that this mutation inhibits PCSK1 enzyme activity and that this inhibition most likely does not involve a strong physical interaction. Furthermore, both mutations PCSK1-p.Asn180Ser and POMC-p.Phe144Leu, which had previously been reported to be associated with severe obesity, were also identified in this study, but did not co-segregate with obesity. Finally, we did not identify any rare mutations co-segregating with obesity in common obesity susceptibility genes, except for CADM2 and QPCTL, where we found two novel variants (p.Arg81His and p.Leu98Pro, respectively) in three obese individuals.

CONCLUSIONS

We showed for the first time that a nonsense mutation in PCSK1 was likely to cause dominantly inherited human obesity, due to the inhibiting properties of the propeptide fragment encoded by the null allele. Furthermore, the present family sequencing design challenged the contribution of previously reported mutations to monogenic or at least severe obesity.

[Testosterone: a treatment for the prevention of cardiovascular disease]

Testosterone treatment was largely prescribed and marketed as a potential therapy to treat symptoms of aging. Testosterone levels decrease progressively with aging and low testosterone levels were associated with an increase risk of cardiovascular events and death. Controversies persist whether this association is causal or mediated by confounders of the general health. Systematic screening of testosterone is not recommended in a check-up visit, but only in case of suggestive symptoms. Furthermore a recent meta-analysis and large prospective cohort studies have reported a concern regarding the safety of testosterone therapy and the associated risk of major cardiovascular events. The decision to prescribe testosterone should be made with the patient after evaluating the risks and benefits.

Novel LEPR mutations in obese Pakistani children identified by PCR-based enrichment and next generation sequencing

OBJECTIVE

Mutations in leptin receptor gene (LEPR) result in early onset extreme adiposity. However, their prevalence in different populations is not known. Indeed, LEPR screening by gold standard Sanger sequencing has been limited by its large size and the cost. One-step PCR-based targeted enrichment could be an option for rapid and cost effective molecular diagnosis of monogenic forms of obesity.

METHODS

The study is based on 39 unrelated severely obese Pakistani children, previously shown to be negative for leptin (LEP) and melanocortin 4 receptor (MC4R) gene mutations, from an initial cohort of 62 probands. Patient samples were analyzed by microdroplet PCR-enrichment (RainDance technologies) targeting coding exons of 26 obesity-associated genes combined with next generation sequencing. Hormone levels were analyzed by ELISA.

RESULTS

The analysis revealed two novel homozygous LEPR mutations, an essential splice site mutation in exon 15 (c.2396-1 G>T), and a nonsense mutation in exon 10 (c.1675 G>A). Both probands had high leptin levels and were phenotypically indistinguishable from age-matched leptin-deficient subjects from the same population.

CONCLUSIONS

The two subjects carrying homozygous LEPR mutations, reported here for the first time in the Pakistani population, constitute 3% of the whole cohort of severely obese children (compared to 17% for LEP and 3% for MC4R).

[What makes a pleasing face]

Regular faces are beautiful because they are expressive and arouse an interest in the observer due to the variations in their shape, their surface appearance and their movements. The sensitivity of the eye of the beholder is correlated to the expressivity of the face and of the dentition. Better, however, to avoid any indication of aggression that could foreshadow the senescence of the face.

Highly sensitive diagnosis of 43 monogenic forms of diabetes or obesity through one-step PCR-based enrichment in combination with next-generation sequencing

OBJECTIVE

Accurate etiological diagnosis of monogenic forms of diabetes and obesity is useful as it can lead to marked improvements in patient care and genetic counseling. Currently, molecular diagnosis based on Sanger sequencing is restricted to only a few genes, as this technology is expensive, time-consuming, and labor-intensive. High-throughput next-generation sequencing (NGS) provides an opportunity to develop innovative cost-efficient methods for sensitive diabetes and obesity multigene screening.

RESEARCH DESIGN AND METHODS

We assessed a new method based on PCR enrichment in microdroplets (RainDance Technologies) and NGS using the Illumina HiSeq2000 for the molecular diagnosis of 43 forms of monogenic diabetes or obesity. Forty patients carrying a known causal mutation for those subtypes according to diagnostic laboratories were blindly reanalyzed.

RESULTS

Except for one variant, we reidentified all causal mutations in each patient associated with an almost-perfect sequencing of the targets (mean of 98.6%). We failed to call one highly complex indel, although we identified a dramatic drop of coverage at this locus. In three patients, we detected other mutations with a putatively deleterious effect in addition to those reported by the genetic diagnostic laboratories.

CONCLUSIONS

Our NGS approach provides an efficient means of highly sensitive screening for mutations in genes associated with monogenic forms of diabetes and obesity. As cost and time to deliver results have been key barriers to uncovering a molecular cause in the many undiagnosed cases likely to exist, the present methodology should be considered in patients displaying features of monogenic diabetes or obesity.

[New developments in cephalometrics]

Recently l recalled the error in the principle which makes cephalometric analysis unsuitable for orthodontic diagnosis. Now, three methods of analysis have been published precisely conceived in order to avoid this error. Will cephalometric analysis succeed in its search for the truth?

[Non diabetic hypoglycemia: diagnosis and management]

Organic or non diabetic hypoglycemia (NDH) is a rare disease when it is confirmed, but is often confounded with low blood glucose concentration (between 3 and 4 mmol/I), which is much more frequent. NDH's definition requires the Whipple triad (plasma glucose level <2.8 mmol/l, symptoms of neuroglycopenia and their relief with administration of sugar). The diagnostic approach needs to differentiate the healthy from the sick patient, who's hypoglycemia causes are multiple and frequent, such as: toxic (medicament, OH), organ deficiency, denutrition and sepsis. When hypoglycemia is suspected, without evident causes in healthy persons, it should be investigated by a 72 h fast test, in order to guide the diagnosis. After confirmation of an endogen hyperinsulinism only, sophisticated imaging should be done to localize the tumor and/or to exclude alternatives diagnosis.

[Sport and type 1 diabetes]

Physical activity is recognised to be an efficient measure in improving glycemic control in the treatment of type 2 diabetes. This evidence is lacking in type I diabetes but type 1I diabetics benefit from the same advantages like the general population. For many type I diabetics, especially younger patients, sport represents an important modality in the treatment of their disease but also of their quality of life. However, this is often a challenge for the patient as well as for the physician regarding the metabolic consequences (hypo- but also hyperglycemia) which can appear in relation with physical activity. There are existing general recommendations concerning the intake of carbohydrates and the reduction of insulin doses but those have to be adapted individually for each patient and depend significantly on different sports and on the intensity of sport.

[Diabetes in elderly: a tailored management]

In developed countries, 12-25 % of the aged population (>65 years old) have diabetes. Treatment of the old diabetic patients is less well studied compared to younger patients although diabetic and geriatric medical associations have issued specific treatment and priority guidelines for these patients. Treatment and targets of glycemic control must be adapted to the functional condition of the patients, prevent symptoms and complications of the geriatric syndrome. Prevention and screening of chronic complication of diabetes have to be integrated in the overall care of aged diabetic patients to optimize their quality of life and health state.

Reassessment of the putative role of BLK-p.A71T loss-of-function mutation in MODY and type 2 diabetes

AIMS/HYPOTHESIS

MODY is believed to be caused by at least 13 different genes. Five rare mutations at the BLK locus, including only one non-synonymous p.A71T variant, were reported to segregate with diabetes in three MODY families. The p.A71T mutation was shown to abolish the enhancing effect of BLK on insulin content and secretion from pancreatic beta cell lines. Here, we reassessed the contribution of BLK to MODY and tested the effect of BLK-p.A71T on type 2 diabetes risk and variations in related traits.

METHODS

BLK was sequenced in 64 unelucidated MODY samples. The BLK-p.A71T variant was genotyped in a French type 2 diabetes case-control study including 4,901 cases and 4,280 controls, and in the DESIR (Data from an Epidemiological Study on the Insulin Resistance Syndrome) and SUVIMAX (Supplementation en Vitamines et Mineraux Antioxydants) population-based cohorts (n = 6,905). The variant effects were assessed by logistic and linear regression models.

RESULTS

No rare non-synonymous BLK mutations were found in the MODY patients. The BLK p.A71T mutation was present in 52 normoglycaemic individuals, making it very unlikely that this loss-of-function mutation causes highly penetrant MODY. We found a nominal association between this variant and increased type 2 diabetes risk, with an enrichment of the mutation in the obese diabetic patients, although no significant association with BMI was identified.

CONCLUSIONS/INTERPRETATION

No mutation in BLK was found in our MODY cohort. From our findings, the BLK-p.A71T mutation may weakly influence type 2 diabetes risk in the context of obesity; however, this will require further validation.

Autonomous and self-sustained circadian oscillators displayed in human islet cells

AIMS/HYPOTHESIS

Following on from the emerging importance of the pancreas circadian clock on islet function and the development of type 2 diabetes in rodent models, we aimed to examine circadian gene expression in human islets. The oscillator properties were assessed in intact islets as well as in beta cells.

METHODS

We established a system for long-term bioluminescence recording in cultured human islets, employing lentivector gene delivery of the core clock gene Bmal1 (also known as Arntl)-luciferase reporter. Beta cells were stably labelled using a rat insulin2 promoter fluorescent construct. Single-islet/cell oscillation profiles were measured by combined bioluminescence-fluorescence time-lapse microscopy.

RESULTS

Human islets synchronised in vitro exhibited self-sustained circadian oscillations of Bmal1-luciferase expression at both the population and single-islet levels, with period lengths of 23.6 and 23.9 h, respectively. Endogenous BMAL1 and CRY1 transcript expression was circadian in synchronised islets over 48 h, and antiphasic to REV-ERBα (also known as NR1D1), PER1, PER2, PER3 and DBP transcript circadian profiles. HNF1A and PDX1 exhibited weak circadian oscillations, in phase with the REV-ERBα transcript. Dispersed islet cells were strongly oscillating as well, at population and single-cell levels. Importantly, beta and non-beta cells revealed oscillatory profiles that were well synchronised with each other.

CONCLUSIONS/INTERPRETATION

We provide for the first time compelling evidence for high-amplitude cell-autonomous circadian oscillators displayed in human pancreatic islets and in dispersed human islet cells. Moreover, these clocks are synchronised between beta and non-beta cells in primary human islet cell cultures.

Biofeedback can reduce foot pressure to a safe level and without causing new at-risk zones in patients with diabetes and peripheral neuropathy

BACKGROUND

Plantar pressure reduction is mandatory for diabetic foot ulcer healing. Our aim was to evaluate the impact of a new walking strategy learned by biofeedback on plantar pressure distribution under both feet in patients with diabetic peripheral neuropathy.

METHODS

Terminally augmented biofeedback has been used for foot off-loading training in 21 patients with diabetic peripheral sensory neuropathy. The biofeedback technique was based on a subjective estimation of performance and objective visual feedback following walking sequences. The patient was considered to have learned a new walking strategy as soon as the peak plantar pressure (PPP) under the previously defined at-risk zone was within a range of 40-80% of baseline PPP in 70% of the totality of steps and during three consecutive walking sequences. The PPP was measured by a portable in-shoe foot pressure measurement system (PEDAR(®)) at baseline (T0), directly after learning (T1) and at 10-day retention test (T2).

RESULTS

The PPP under at-risk zones decreased significantly at T1 (165 ± 9 kPa, p < 0.0001) and T2 (167 ± 11, p = 0.001), as compared with T0 (242 ± 12 kPa) without any increase of the PPP elsewhere. At the contralateral foot (not concerned by off-loading), the PPP was slightly higher under the lateral midfoot at T1 (68 ± 8 kPa, p = 0.01) and T2 (65 ± 8 kPa, p = 0.01), as compared with T0 (58 ± 6 kPa).

CONCLUSIONS

The foot off-loading by biofeedback leads to a safe and regular plantar pressure distribution without inducing any new 'at-risk' area under both feet.

Non-alcoholic fatty liver disease and insulin resistance: from bench to bedside

Non-alcoholic fatty liver disease (NAFLD) is now the most frequent chronic liver disease in the developed countries. There is also growing evidence from basic and clinical research that NAFLD has a strong relationship to insulin resistance, which is a key factor in the development of type 2 diabetes. The aim of this review is to summarize the recent important findings linking NAFLD and insulin resistance. Lipid accumulation, particularly of diacylglycerol, appears to be of major importance in this process. Mitochondrial dysfunction, through decreased mitochondrial biogenesis, increases oxidative stress, and ageing also plays an important role. Finally, endoplasmic reticulum stress and inflammation also probably contribute to the development of insulin resistance via mechanisms that are still not well understood. Clinical aspects of NAFLD, such as its diagnosis and management, are also investigated in this review.

Familial early-onset diabetes is not a typical MODY in several Tunisian patients

BACKGROUND

MODY (Maturity-onset diabetes of the young), a dominantly inherited form of early-onset diabetes, is clinically and genetically heterogeneous with more than ten genetic subtypes described worldwide.

AIM

To evaluate the possible existence of MODY in 12 young diabetic Tunisian patients by searching for mutations in the most prevalent MODY genes.

METHODS

Twelve patients with diabetes in 2-to-3 generations, all diagnosed before age 31, were screened for mutations and deletions in HNF1A, HNF4A, INS, IPF1, NEUROD1 and GCK genes by Sanger sequencing and by Multiplex ligation-dependent probe amplification assay.

RESULTS

The patients had no evidence of autoimmunity and a mean age at diabetes diagnosis of 25.66 ± 3.96 years with severe overt diabetes (fasting glycaemia: 10.91 ± 3.55 mmol/ l; HbA1c: 10.46 ± 3.31 %). Two subjects were initially treated with insulin. On the ten initially treated with OHA or on diet, eight converted to insulin therapy (within 3 months to 20 years). Molecular analysis showed only one missense HNF4A mutation (I453V) in one family. No mutations in the studied genes were detected in the other patients.

CONCLUSION

A molecular defect in known MODY genes has been excluded in 11 patients with early-onset diabetes suggesting that other genetic causes may explain diabetes in these families. In such cases, new generation sequencing approaches may be well appropriate to identify specific molecular etiologies from extended families and to establish a strategy of molecular diagnostic of MODY in Tunisia.

[Search of a cephalometric reference line]

The variability of cephalometric reference lines is examined in this article with regard to typology, natural orientation of the head, orientation by the vestibular system, and anatomy. It appears that these lines have orientations that vary with individual subjects, that is, a line is not the same in a specific person as it is in a theoretical model that is based on average values. It follows from this that the deviation observed between a patient's measurement and the average could just as well reflect variations in the reference lines as it does of those of the structures being studied. Such a measurement cannot, accordingly, serve as the basis for a morphological diagnosis. To deal with this problem, we propose another cephalometric reference system that presents, for orthognathic diagnosis, many advantages over the traditional system but, itself, remains imperfect.

Whole-exome sequencing and high throughput genotyping identified KCNJ11 as the thirteenth MODY gene

Background

Maturity-onset of the young (MODY) is a clinically heterogeneous form of diabetes characterized by an autosomal-dominant mode of inheritance, an onset before the age of 25 years, and a primary defect in the pancreatic beta-cell function. Approximately 30% of MODY families remain genetically unexplained (MODY-X). Here, we aimed to use whole-exome sequencing (WES) in a four-generation MODY-X family to identify a new susceptibility gene for MODY.

Methodology

WES (Agilent-SureSelect capture/Illumina-GAIIx sequencing) was performed in three affected and one non-affected relatives in the MODY-X family. We then performed a high-throughput multiplex genotyping (Illumina-GoldenGate assay) of the putative causal mutations in the whole family and in 406 controls. A linkage analysis was also carried out.

Principal Findings

By focusing on variants of interest (i.e. gains of stop codon, frameshift, non-synonymous and splice-site variants not reported in dbSNP130) present in the three affected relatives and not present in the control, we found 69 mutations. However, as WES was not uniform between samples, a total of 324 mutations had to be assessed in the whole family and in controls. Only one mutation (p.Glu227Lys in KCNJ11) co-segregated with diabetes in the family (with a LOD-score of 3.68). No KCNJ11 mutation was found in 25 other MODY-X unrelated subjects.

Conclusions/Significance

Beyond neonatal diabetes mellitus (NDM), KCNJ11 is also a MODY gene (‘MODY13’), confirming the wide spectrum of diabetes related phenotypes due to mutations in NDM genes (i.e. KCNJ11, ABCC8 and INS). Therefore, the molecular diagnosis of MODY should include KCNJ11 as affected carriers can be ideally treated with oral sulfonylureas.

[Diabetic nephropathy: an update]

Diabetes has a constantly growing prevalence and leads to a number of complications such as diabetic nephropathy. A systematic screening and an adapted management are needed to limit the renal and also the cardiovascular complications linked to diabetic nephropathy. An adequate glycemic and tensional control and control of proteinuria are the priority in the care of diabetic nephropathy. Other aspects such as phospho-calcium balance, lipid panel or lifestyle changes are also important and therefore a multidisciplinary approach is essential. A better understanding of the physiopathology may lead to even more effective treatments in the future. We resume in this article the actual management of a patient suffering from diabetic nephropathy and the future treatment perspectives.

Clinical and metabolic features of adult-onset diabetes caused by ABCC8 mutations

OBJECTIVE

Gain-of-function ABCC8/sulfonylurea (SU) receptor 1 mutations cause neonatal diabetes mellitus (NDM) or late-onset diabetes in adult relatives. Given the effectiveness of SU treatment in ABCC8-NDM patients, we further characterized late-onset ABCC8-associated diabetes.

RESEARCH DESIGN AND METHODS

Seven adult subjects from three NDM families and one family with type 2 diabetes were studied. Insulin secretion and insulin sensitivity were assessed using clamp techniques. We screened 139 type 2 diabetic patients who were well controlled by SU for ABCC8 mutations.

RESULTS

ABCC8 mutation carriers exhibited glucose intolerance, frank diabetes, or insulin-requiring diabetes since diagnosis. HbA(1c) improved in five SU-treated patients. Insulin secretion capacity was impaired in three patients compared with adult control subjects but was restored after a 4-week SU trial in two patients. Cohort screening revealed four SU-treated patients with ABCC8 mutations, two of which are likely causal.

CONCLUSIONS

Although of rare occurrence, recognition of adult-onset ABCC8-associated diabetes may help in targeting patients for SU therapy.

Human mutation within Per-Arnt-Sim (PAS) domain-containing protein kinase (PASK) causes basal insulin hypersecretion

PAS kinase (PASK) is a glucose-regulated protein kinase involved in the control of pancreatic islet hormone release and insulin sensitivity. We aimed here to identify mutations in the PASK gene that may be associated with young-onset diabetes in humans. We screened 18 diabetic probands with unelucidated maturity-onset diabetes of the young (MODY). We identified two rare nonsynonymous mutations in the PASK gene (p.L1051V and p.G1117E), each of which was found in a single MODY family. Wild type or mutant PASKs were expressed in HEK 293 cells. Kinase activity of the affinity-purified proteins was assayed as autophosphorylation at amino acid Thr307 or against an Ugp1p-derived peptide. Whereas the PASK p.G1117E mutant displayed a ∼25% increase with respect to wild type PASK in the extent of autophosphorylation, and a ∼2-fold increase in kinase activity toward exogenous substrates, the activity of the p.L1051V mutant was unchanged. Amino acid Gly1117 is located in an α helical region opposing the active site of PASK and may elicit either: (a) a conformational change that increases catalytic efficiency or (b) a diminished inhibitory interaction with the PAS domain. Mouse islets were therefore infected with adenoviruses expressing wild type or mutant PASK and the regulation of insulin secretion was examined. PASK p.G1117E-infected islets displayed a 4-fold decrease in glucose-stimulated (16.7 versus 3 mM) insulin secretion, chiefly reflecting a 4.5-fold increase in insulin release at low glucose. In summary, we have characterized a rare mutation (p.G1117E) in the PASK gene from a young-onset diabetes family, which modulates glucose-stimulated insulin secretion.