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ABSTRACT: As well as improving diagnostic and clinical outcomes for affected patients, understanding the genetic basis of rare human metabolic disorders has resulted in several fundamental biological insights. In some cases understanding extreme phenotypes has also informed thinking about more prevalent metabolic diseases. Insulin resistance underpins the twin epidemics of obesity and type 2 diabetes as well as accounting for many of the metabolic problems encompassed by the term metabolic syndrome. This review provides a brief update on current understanding of human severe insulin resistance syndromes, before highlighting recent insights provided by studies in these rare syndromes into the molecular pathogenesis of elements of the metabolic syndrome.
Best practice & research. Clinical endocrinology & metabolism 04/2012; 26(2):145-57. · 3.89 Impact Factor
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ABSTRACT: Recent human genetic studies have established that neurokinin B (NKB) signalling via the neurokinin 3 receptor (NK3R) is required for normal developmental activation of pulsatile GnRH secretion from the hypothalamus. As increasing numbers of patients with loss-of-function mutations have been described, evidence has emerged that peripheral NKB is not necessary for normal pregnancy despite high placental expression and high plasma levels of NKB in late gestation. Nevertheless many key questions about the role of NKB in the function of the GnRH pulse generator remain to be answered. Differences in requirement for NKB/NK3R for hypothalamic-pituitary-gonadal (HPG) maturation amongst different species, and their varied responses to stimulation with NKB represent a challenge for higher resolution studies. Neuroanatomical investigation has, however, identified key "KNDy" (Kisspeptin, Neurokinin B, Dynorphin) arcuate neurones that are conserved amongst different species and that are intimately connected both to each other and to the GnRH nerve termini. Several lines of evidence suggest that these may be the core of the GnRH pulse generator, and with experimental tools now in place in humans, monkeys and other experimental animals to pursue the function of these interconnected neurones and the functional hierarchy of their neuroendocrine inputs, understanding of the enigmatic GnRH pulse generator may at last be within reach.
Molecular and Cellular Endocrinology 07/2011; 346(1-2):57-64. · 4.19 Impact Factor
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Tuomas O Kilpeläinen,
M Carola Zillikens,
Alena Stančákova,
Francis M Finucane,
Janina S Ried,
Claudia Langenberg,
Weihua Zhang,
Jacques S Beckmann,
Jian'an Luan,
Liesbeth Vandenput, [......],
Joel N Hirschhorn,
Kari Stefansson,
H-Erich Wichmann,
Claes Ohlsson,
Stephen O'Rahilly,
Nicholas J Wareham,
Elizabeth K Speliotes,
Caroline S Fox,
Markku Laakso,
Ruth J F Loos
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ABSTRACT: Genome-wide association studies have identified 32 loci influencing body mass index, but this measure does not distinguish lean from fat mass. To identify adiposity loci, we meta-analyzed associations between ∼2.5 million SNPs and body fat percentage from 36,626 individuals and followed up the 14 most significant (P < 10(-6)) independent loci in 39,576 individuals. We confirmed a previously established adiposity locus in FTO (P = 3 × 10(-26)) and identified two new loci associated with body fat percentage, one near IRS1 (P = 4 × 10(-11)) and one near SPRY2 (P = 3 × 10(-8)). Both loci contain genes with potential links to adipocyte physiology. Notably, the body-fat-decreasing allele near IRS1 is associated with decreased IRS1 expression and with an impaired metabolic profile, including an increased visceral to subcutaneous fat ratio, insulin resistance, dyslipidemia, risk of diabetes and coronary artery disease and decreased adiponectin levels. Our findings provide new insights into adiposity and insulin resistance.
Nature Genetics 06/2011; 43(8):753-60. · 35.53 Impact Factor
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Tuomas O Kilpeläinen,
M Carola Zillikens,
Alena,
Francis M Finucane,
Janina S Ried,
Claudia Langenberg,
Weihua Zhang,
Jacques S Beckmann,
Luan,
Liesbeth Vandenput, [......],
Joel N Hirschhorn,
Kari Stefansson,
H-Erich Wichmann,
Claes Ohlsson,
Stephen,
Nicholas J Wareham,
Elizabeth K Speliotes,
Caroline S Fox,
Markku Laakso,
Ruth J F Loos
Nature Genetics 06/2011; 43(8):753-760. · 35.53 Impact Factor
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ABSTRACT: Genetic testing in inherited disease has traditionally relied upon recognition of the presenting clinical syndrome and targeted analysis of genes known to be linked to that syndrome. Consequently, many patients with genetic syndromes remain without a specific diagnosis.
New 'next-generation' sequencing (NGS) techniques permit simultaneous sequencing of enormous amounts of DNA. A slew of research publications have recently demonstrated the tremendous power of these technologies in increasing understanding of human genetic disease.
These approaches are likely to be increasingly employed in routine diagnostic practice, but the scale of the genetic information yielded about individuals means that caution must be exercised to avoid net harm in this setting.
Use of NGS in a research setting will increasingly have a major but indirect beneficial impact on clinical practice. However, important technical, ethical and social challenges need to be addressed through informed professional and public dialogue before it finds its mature niche as a direct tool in the clinical diagnostic armoury.
British Medical Bulletin 06/2011; 99:53-71. · 4.54 Impact Factor
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Alison Sleigh,
Philippa Raymond-Barker,
Kerrie Thackray,
David Porter,
Mensud Hatunic,
Alessandra Vottero,
Christine Burren,
Catherine Mitchell,
Martin McIntyre,
Soren Brage,
T Adrian Carpenter,
Peter R Murgatroyd,
Kevin M Brindle,
Graham J Kemp,
Stephen O'Rahilly, Robert K Semple,
David B Savage
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ABSTRACT: Mitochondrial dysfunction is associated with insulin resistance and type 2 diabetes. It has thus been suggested that primary and/or genetic abnormalities in mitochondrial function may lead to accumulation of toxic lipid species in muscle and elsewhere, impairing insulin action on glucose metabolism. Alternatively, however, defects in insulin signaling may be primary events that result in mitochondrial dysfunction, or there may be a bidirectional relationship between these phenomena. To investigate this, we examined mitochondrial function in patients with genetic defects in insulin receptor (INSR) signaling. We found that phosphocreatine recovery after exercise, a measure of skeletal muscle mitochondrial function in vivo, was significantly slowed in patients with INSR mutations compared with that in healthy age-, fitness-, and BMI-matched controls. These findings suggest that defective insulin signaling may promote mitochondrial dysfunction. Furthermore, consistent with previous studies of mouse models of mitochondrial dysfunction, basal and sleeping metabolic rates were both significantly increased in genetically insulin-resistant patients, perhaps because mitochondrial dysfunction necessitates increased nutrient oxidation in order to maintain cellular energy levels.
The Journal of clinical investigation 06/2011; 121(6):2457-61. · 15.39 Impact Factor
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ABSTRACT: Insulin resistance is among the most prevalent endocrine derangements in the world, and it is closely associated with major diseases of global reach including diabetes mellitus, atherosclerosis, nonalcoholic fatty liver disease, and ovulatory dysfunction. It is most commonly found in those with obesity but may also occur in an unusually severe form in rare patients with monogenic defects. Such patients may loosely be grouped into those with primary disorders of insulin signaling and those with defects in adipose tissue development or function (lipodystrophy). The severe insulin resistance of both subgroups puts patients at risk of accelerated complications and poses severe challenges in clinical management. However, the clinical disorders produced by different genetic defects are often biochemically and clinically distinct and are associated with distinct risks of complications. This means that optimal management of affected patients should take into account the specific natural history of each condition. In clinical practice, they are often underdiagnosed, however, with low rates of identification of the underlying genetic defect, a problem compounded by confusing and overlapping nomenclature and classification. We now review recent developments in understanding of genetic forms of severe insulin resistance and/or lipodystrophy and suggest a revised classification based on growing knowledge of the underlying pathophysiology.
Endocrine reviews 05/2011; 32(4):498-514. · 19.76 Impact Factor
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Sheetal Gandotra,
Caroline Le Dour,
William Bottomley,
Pascale Cervera,
Philippe Giral,
Yves Reznik,
Guillaume Charpentier,
Martine Auclair,
Marc Delépine,
Inês Barroso, Robert K Semple,
Mark Lathrop,
Olivier Lascols,
Jacqueline Capeau,
Stephen O'Rahilly,
Jocelyne Magré,
David B Savage,
Corinne Vigouroux
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ABSTRACT: Perilipin is the most abundant adipocyte-specific protein that coats lipid droplets, and it is required for optimal lipid incorporation and release from the droplet. We identified two heterozygous frameshift mutations in the perilipin gene (PLIN1) in three families with partial lipodystrophy, severe dyslipidemia, and insulin-resistant diabetes. Subcutaneous fat from the patients was characterized by smaller-than-normal adipocytes, macrophage infiltration, and fibrosis. In contrast to wild-type perilipin, mutant forms of the protein failed to increase triglyceride accumulation when expressed heterologously in preadipocytes. These findings define a novel dominant form of inherited lipodystrophy and highlight the serious metabolic consequences of a primary defect in the formation of lipid droplets in adipose tissue.
New England Journal of Medicine 02/2011; 364(8):740-8. · 53.30 Impact Factor
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Isabel Huang-Doran,
Louise S Bicknell,
Francis M Finucane,
Nuno Rocha,
Keith M Porter,
Y C Loraine Tung,
Ferenc Szekeres,
Anna Krook,
John J Nolan,
Mark O'Driscoll,
Michael Bober,
Stephen O'Rahilly,
Andrew P Jackson, Robert K Semple
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ABSTRACT: Genetic defects in human pericentrin (PCNT), encoding the centrosomal protein pericentrin, cause a form of osteodysplastic primordial dwarfism that is sometimes reported to be associated with diabetes. We thus set out to determine the prevalence of diabetes and insulin resistance among patients with PCNT defects and examined the effects of pericentrin depletion on insulin action using 3T3-L1 adipocytes as a model system.
A cross-sectional metabolic assessment of 21 patients with PCNT mutations was undertaken. Pericentrin expression in human tissues was profiled using quantitative real-time PCR. The effect of pericentrin knockdown on insulin action and adipogenesis in 3T3-L1 adipocytes was determined using Oil red O staining, gene-expression analysis, immunoblotting, and glucose uptake assays. Pericentrin expression and localization also was determined in skeletal muscle.
Of 21 patients with genetic defects in PCNT, 18 had insulin resistance, which was severe in the majority of subjects. Ten subjects had confirmed diabetes (mean age of onset 15 years [range 5-28]), and 13 had metabolic dyslipidemia. All patients without insulin resistance were younger than 4 years old. Knockdown of pericentrin in adipocytes had no effect on proximal insulin signaling but produced a twofold impairment in insulin-stimulated glucose uptake, approximately commensurate with an associated defect in cell proliferation and adipogenesis. Pericentrin was highly expressed in human skeletal muscle, where it showed a perinuclear distribution.
Severe insulin resistance and premature diabetes are common features of PCNT deficiency but are not congenital. Partial failure of adipocyte differentiation may contribute to this, but pericentrin deficiency does not impair proximal insulin action in adipocytes.
Diabetes 01/2011; 60(3):925-35. · 8.29 Impact Factor
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Eleanor Raffan,
Liam A Hurst,
Saeed Al Turki,
Gillian Carpenter,
Carol Scott,
Allan Daly,
Alison Coffey,
Sanjeev Bhaskar,
Eleanor Howard,
Naz Khan,
Helen Kingston,
Aarno Palotie,
David B Savage,
Mark O'Driscoll,
Claire Smith,
Stephen O'Rahilly,
Inês Barroso, Robert K Semple
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ABSTRACT: Genetic diagnosis of inherited metabolic disease is conventionally achieved through syndrome recognition and targeted gene sequencing, but many patients receive no specific diagnosis. Next-generation sequencing allied to capture of expressed sequences from genomic DNA now offers a powerful new diagnostic approach. Barriers to routine diagnostic use include cost, and the complexity of interpreting results arising from simultaneous identification of large numbers of variants. We applied exome-wide sequencing to an individual, 16-year-old daughter of consanguineous parents with a novel syndrome of short stature, severe insulin resistance, ptosis, and microcephaly. Pulldown of expressed sequences from genomic DNA followed by massively parallel sequencing was undertaken. Single nucleotide variants were called using SAMtools prior to filtering based on sequence quality and existence in control genomes and exomes. Of 485 genetic variants predicted to alter protein sequence and absent from control data, 24 were homozygous in the patient. One mutation - the p.Arg732X mutation in the WRN gene - has previously been reported in Werner's syndrome (WS). On re-evaluation of the patient several early features of WS were detected including loss of fat from the extremities and frontal hair thinning. Lymphoblastoid cells from the proband exhibited a defective decatenation checkpoint, consistent with loss of WRN activity. We have thus diagnosed WS some 15 years earlier than average, permitting aggressive prophylactic therapy and screening for WS complications, illustrating the potential of exome-wide sequencing to achieve early diagnosis and change management of rare autosomal recessive disease, even in individual patients of consanguineous parentage with apparently novel syndromes.
Frontiers in endocrinology. 01/2011; 2:8.
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ABSTRACT: To summarize recent research into the mechanisms linking insulin resistance, nonalcoholic fatty liver disease and metabolic dyslipidaemia.
Pathologically increased nonesterified fatty acids have widely been viewed as a key driver of hepatic insulin resistance/nonalcoholic fatty liver disease/metabolic dyslipidaemia. However, this may have been overestimated, and growing evidence now also implicates dysregulated hepatic de-novo lipogenesis in the pathogenesis of these phenomena. This is driven by the action of hyperinsulinaemia on the liver, mediated by PI3 kinase, though consensus on the downstream effectors remains to be reached. Endoplasmic reticulum stress and/or components of the attendant unfolded protein response have also emerged as players in dysregulated hepatic metabolism due to nutritional overload. Several points of convergence between metabolic and unfolded protein response pathways have been described, notably centring on the transcription factor XBP1.
Insulin resistance, nonalcoholic fatty liver disease and metabolic dyslipidaemia are inextricably linked and need to be considered together. Modelling and dissecting prevalent forms of the disease is complex, but unrestrained de-novo lipogenesis driven by hyperinsulinaemia appears to play an important role. Endoplasmic reticulum stress and the associated unfolded protein response may also contribute to cellular mismatch between triglyceride secretion/metabolism and synthesis, though a complete picture has yet to emerge.
Current opinion in lipidology 08/2010; 21(4):329-36. · 6.13 Impact Factor
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ABSTRACT: Management of severe insulin resistance (IR) is a major clinical challenge in many patients with obesity or lipodystrophy, and also in rarer patients with proven or suspected genetic defects in the insulin receptor or downstream signalling. The latter group can present at any time between birth and early adult life, with a variable clinical course broadly correlated with the severity of IR. Primary insulin signalling defects are usually associated with poor weight gain rather than obesity. Initially, extreme hyperinsulinaemia produces ovarian enlargement and hyperandrogenism in women, and often fasting or postprandial hypoglycaemia. However, any hypoglycaemia gradually evolves into insulin-resistant hyperglycaemia when beta cell function declines. Optimal management of these complex disorders depends on early diagnosis and appropriate targeting of both high and low glucose levels. In newborns, continuous nasogastric feeding may reduce harmful glycaemic fluctuations, and in older patients, acarbose may mitigate postprandial hypoglycaemia. Insulin sensitization, initially with metformin but later with trials of additional agents such as thiazolidinediones, is the mainstay of early therapy, but insulin replacement, eventually with very high doses, is required once diabetes has supervened. Preliminary data suggest that rhIGF-1 can improve survival in infants with the most severe insulin receptor defects and also improve beta cell function in older patients with milder receptoropathies. The utility of newer therapies such as glucagon-like peptide-1 agonists and dipeptidyl peptidase-IV inhibitors remains untested in this condition. Thus, management of these patients remains largely empirical, and there is a pressing need to collate data centrally to optimize treatment algorithms.
Clinical Endocrinology 04/2010; 73(3):286-90. · 3.17 Impact Factor
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ABSTRACT: Diabetes in the context of severe insulin resistance (SIR) presents a major therapeutic challenge because conventional therapies including insulin and insulin sensitizers often fail to achieve adequate metabolic control. Adjunctive therapy with recombinant human IGF-I (rhIGF-I)/recombinant human IGF binding protein-3 (rhIGFBP-3) has been shown to improve insulin sensitivity in both type 1 and type 2 diabetes and may have a role in the treatment of SIR. We report clinical and physiological outcomes after adjunctive therapy with rhIGF-I/rhIGFBP-3 in five subjects with SIR.
Five females (median age, 17 yr; range, 5-37) with SIR (two with pathogenic insulin receptor mutations) were treated with 0.5-2.0 mg/kg rhIGF-I/rhIGFBP-3 using a 16-wk dose escalation protocol. Glycosylated hemoglobin was recorded monthly. At baseline and end of treatment all patients were evaluated using continuous glucose monitoring sensing and admitted for overnight GH profiling and insulin-modified stable-label iv glucose tolerance test. Changes in body composition were assessed using dual-energy x-ray absorptiometry and magnetic resonance imaging.
Treatment with rhIGF-I/rhIGFBP-3 was well tolerated, and all subjects reported clinical improvements with reduction in acanthosis nigricans. Glycosylated hemoglobin was reduced (8.5% pretreatment to 7.1%; P < 0.03) with a trend toward reduction in mean continuous glucose monitoring sensing glucose (10.7 vs. 8.5 mmol/liter; P = 0.08). Effects of treatment on other biochemical measures were variable, but there was a trend toward improved C-peptide responses during the iv glucose tolerance test.
rhIGF-I/rhIGFBP-3 is well tolerated and clinically effective in subjects with SIR.
The Journal of clinical endocrinology and metabolism 03/2010; 95(5):2113-22. · 6.50 Impact Factor
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ABSTRACT: Adiponectin is a highly abundant plasma protein synthesized nearly exclusively in adipose tissue from the ADIPOQ gene. It has excited intense interest because of robust correlation of its circulating levels with indices of insulin resistance (IR) and risk of type 2 diabetes, and their unusual inverse relationship with fat mass. It has been suggested that pharmacological strategies aimed at augmenting adiponectin levels or action may generate novel insulin-sensitizing drugs.
Relevant publications were identified by searching PubMed, with secondary searches of their bibliographies.
Rodent studies suggest that adiponectin exerts a direct insulin-sensitizing effect on the liver, consistent with a role in the pathogenesis of prevalent forms of IR and its sequelae. However, the complex higher-order structure of adiponectin and inconsistent reports regarding its putative receptors have complicated efforts to understand the mechanistic basis of this. No proof yet exists that adiponectin modulates insulin sensitivity in humans, and genetic, biochemical, and physiological evidence suggests that low adiponectin levels may be a consequence of IR with compensatory hyperinsulinemia. This suggests that there may be a bidirectional relationship between IR and hypoadiponectinemia in humans.
The relationship between adiponectin and insulin action in humans is more complex than often suggested. Further investigation of the direction of causality in this relationship, allied to studies of the cellular mechanisms involved, will be central to improving understanding of the physiological role of this enigmatic protein, and to efforts to exploit it for therapeutic benefit.
The Journal of clinical endocrinology and metabolism 02/2010; 95(4):1544-54. · 6.50 Impact Factor
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ABSTRACT: The hypothalamus integrates multiple environmental and developmental cues relevant to reproductive function, serving to transduce these into a pulsatile output of gonadotropin-releasing hormone (GnRH). Although neuroanatomical and physiological studies have yielded key clues about the functional organisation of the so-called 'GnRH pulse generator', only in the last decade have the molecular components of the circuitry upstream from GnRH begun to be elucidated. A major contributor to this has been human genetics, through identification of mutations causing isolated hypogonadotropic hypogonadism (IHH) without developmental defects. The greatest success of this approach was the finding in 2003 that mutations of KISS1R cause IHH, producing a quantum leap in understanding of regulation of GnRH secretion, and energising the field. New evidence has now emerged that loss of function of neurokinin B (NKB) or its receptor, the neurokinin-3 receptor, produces IHH of similar severity to that caused by KISS1R mutations in humans. Preliminary evidence suggests that the role of NKB in reproductive function differs significantly between humans and rodents, posing challenges for future studies. We review the human genetics of NKB and its receptor, and discuss the future work required to elucidate their precise role in the regulation of human GnRH secretion.
Frontiers of hormone research 01/2010; 39:133-41. · 1.71 Impact Factor
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J Brent Richards,
Dawn Waterworth,
Stephen O'Rahilly,
Marie-France Hivert,
Ruth J F Loos,
John R B Perry,
Toshiko Tanaka,
Nicholas John Timpson, Robert K Semple,
Nicole Soranzo, [......],
Panos Deloukas,
Tomi Pastinen,
Nilesh J Samani,
Ruth McPherson,
George Davey Smith,
Timothy M Frayling,
Nicholas J Wareham,
James B Meigs,
Vincent Mooser,
Tim D Spector
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ABSTRACT: The adipocyte-derived protein adiponectin is highly heritable and inversely associated with risk of type 2 diabetes mellitus (T2D) and coronary heart disease (CHD). We meta-analyzed 3 genome-wide association studies for circulating adiponectin levels (n = 8,531) and sought validation of the lead single nucleotide polymorphisms (SNPs) in 5 additional cohorts (n = 6,202). Five SNPs were genome-wide significant in their relationship with adiponectin (P< or =5x10(-8)). We then tested whether these 5 SNPs were associated with risk of T2D and CHD using a Bonferroni-corrected threshold of P< or =0.011 to declare statistical significance for these disease associations. SNPs at the adiponectin-encoding ADIPOQ locus demonstrated the strongest associations with adiponectin levels (P-combined = 9.2x10(-19) for lead SNP, rs266717, n = 14,733). A novel variant in the ARL15 (ADP-ribosylation factor-like 15) gene was associated with lower circulating levels of adiponectin (rs4311394-G, P-combined = 2.9x10(-8), n = 14,733). This same risk allele at ARL15 was also associated with a higher risk of CHD (odds ratio [OR] = 1.12, P = 8.5x10(-6), n = 22,421) more nominally, an increased risk of T2D (OR = 1.11, P = 3.2x10(-3), n = 10,128), and several metabolic traits. Expression studies in humans indicated that ARL15 is well-expressed in skeletal muscle. These findings identify a novel protein, ARL15, which influences circulating adiponectin levels and may impact upon CHD risk.
PLoS Genetics 12/2009; 5(12):e1000768. · 8.69 Impact Factor
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ABSTRACT: The complex organization and regulation of the human hypothalamic-pituitary-gonadal axis render it susceptible to dysfunction in the face of a variety of genetic insults, leading to different degrees of hypogonadotrophic hypogonadism (HH). Although the genetic basis of some HH was recognized more than 60 years ago the first specific pathogenic defect, in the KAL1 gene, was only identified within the last 20 years. In the past decade, the rate of genetic discovery has dramatically accelerated, with defects in more than 10 genes now associated with HH. Several themes have emerged as the genetic basis of HH has gradually been uncovered, including the association of some genes such as FGFR1, FGF8, PROK2 and PROKR2, both with HH in association with hyposmia/anosmia (Kallmann syndrome) and with normosmic HH, thus blurring the clinical distinction between ontogenic and purely functional defects in the axis. Many examples of digenic inheritance of HH have also been reported, sometimes producing variable reproductive and accessory phenotypes within a family with non-Mendelian inheritance patterns. In strictly normosmic HH, human genetics has made a particularly dramatic impact in the past 6 years through homozygosity mapping in consanguineous families, first through identification of a key role for kisspeptin in triggering GnRH release, and very recently through demonstration of a critical role for neurokinin B in normal sexual maturation. This review summarises current understanding of the genetic architecture of HH, as well as its diagnostic and mechanistic implications.
Clinical Endocrinology 09/2009; 72(4):427-35. · 3.17 Impact Factor
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Tulay Guran,
Gwen Tolhurst,
Abdullah Bereket,
Nuno Rocha,
Keith Porter,
Serap Turan,
Fiona M Gribble,
L Damla Kotan,
Teoman Akcay,
Zeynep Atay,
Husniye Canan,
Ayse Serin,
Stephen O'Rahilly,
Frank Reimann, Robert K Semple,
A Kemal Topaloglu
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ABSTRACT: The neurokinin B (NKB) receptor, encoded by TACR3, is widely expressed within the central nervous system, including hypothalamic nuclei involved in regulating GnRH release. We have recently reported two mutations in transmembrane segments of the receptor and a missense mutation in NKB in patients with normosmic isolated hypogonadotropic hypogonadism (nIHH).
We sequenced the TACR3 gene in a family in which three siblings had nIHH. The novel mutant receptor thus identified was studied in a heterologous expression system using calcium flux as the functional readout.
All affected siblings were homozygous for the His148Leu mutation, in the first extracellular loop of the NKB receptor. The His148Leu mutant receptor exhibited profoundly impaired signaling in response to NKB (EC(50) = 3 +/- 0.1 nm and >5 microm for wild-type and His148Leu, respectively). The location of the mutation in an extracellular part of the receptor led us also to test whether senktide, a synthetic NKB analog, may retain ability to stimulate the mutant receptor. However, the signaling activity of the His148Leu receptor in response to senktide was also severely impaired (EC(50) = 1 +/- 1 nm for wild-type and no significant response of His148Leu to 10 microm).
Homozygosity for the TACR3 His148Leu mutation leads to failure of sexual maturation in humans, whereas signaling by the mutant receptor in vitro in response to either NKB or senktide is severely impaired. These observations further strengthen the link between NKB, the NKB receptor, and regulation of human reproductive function.
The Journal of clinical endocrinology and metabolism 09/2009; 94(10):3633-9. · 6.50 Impact Factor
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Oscar Rubio-Cabezas,
Vishwajeet Puri,
Incoronata Murano,
Vladimir Saudek, Robert K Semple,
Satya Dash,
Caroline S S Hyden,
William Bottomley,
Corinne Vigouroux,
Jocelyne Magré, [......],
Sara Suliman,
Ann-Marie Patch,
Anil K Agarwal,
Abhimanyu Garg,
Inês Barroso,
Saverio Cinti,
Michael P Czech,
Jesús Argente,
Stephen O'Rahilly,
David B Savage
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ABSTRACT: Lipodystrophic syndromes are characterized by adipose tissue deficiency. Although rare, they are of considerable interest as they, like obesity, typically lead to ectopic lipid accumulation, dyslipidaemia and insulin resistant diabetes. In this paper we describe a female patient with partial lipodystrophy (affecting limb, femorogluteal and subcutaneous abdominal fat), white adipocytes with multiloculated lipid droplets and insulin-resistant diabetes, who was found to be homozygous for a premature truncation mutation in the lipid droplet protein cell death-inducing Dffa-like effector C (CIDEC) (E186X). The truncation disrupts the highly conserved CIDE-C domain and the mutant protein is mistargeted and fails to increase the lipid droplet size in transfected cells. In mice, Cidec deficiency also reduces fat mass and induces the formation of white adipocytes with multilocular lipid droplets, but in contrast to our patient, Cidec null mice are protected against diet-induced obesity and insulin resistance. In addition to describing a novel autosomal recessive form of familial partial lipodystrophy, these observations also suggest that CIDEC is required for unilocular lipid droplet formation and optimal energy storage in human fat.
EMBO Molecular Medicine 08/2009; 1(5):280-7. · 10.33 Impact Factor
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Satya Dash,
Hiroyuki Sano,
Justin J Rochford, Robert K Semple,
Giles Yeo,
Caroline S S Hyden,
Maria A Soos,
James Clark,
Andrew Rodin,
Claudia Langenberg,
Celine Druet,
Katherine A Fawcett,
Y C Loraine Tung,
Nicolas J Wareham,
Inês Barroso,
Gustav E Lienhard,
Stephen O'Rahilly,
David B Savage
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ABSTRACT: Tre-2, BUB2, CDC16, 1 domain family member 4 (TBC1D4) (AS160) is a Rab-GTPase activating protein implicated in insulin-stimulated glucose transporter 4 (GLUT4) translocation in adipocytes and myotubes. To determine whether loss-of-function mutations in TBC1D4 might impair GLUT4 translocation and cause insulin resistance in humans, we screened the coding regions of this gene in 156 severely insulin-resistant patients. A female presenting at age 11 years with acanthosis nigricans and extreme postprandial hyperinsulinemia was heterozygous for a premature stop mutation (R363X) in TBC1D4. After demonstrating reduced expression of wild-type TBC1D4 protein and expression of the truncated protein in lymphocytes from the proband, we further characterized the biological effects of the truncated protein in 3T3L1 adipocytes. Prematurely truncated TBC1D4 protein tended to increase basal cell membrane GLUT4 levels (P = 0.053) and significantly reduced insulin-stimulated GLUT4 cell membrane translocation (P < 0.05). When coexpressed with wild-type TBC1D4, the truncated protein dimerized with full-length TBC1D4, suggesting that the heterozygous truncated variant might interfere with its wild-type counterpart in a dominant negative fashion. Two overweight family members with the mutation also manifested normal fasting glucose and insulin levels but disproportionately elevated insulin levels following an oral glucose challenge. This family provides unique genetic evidence of TBC1D4 involvement in human insulin action.
Proceedings of the National Academy of Sciences 06/2009; 106(23):9350-5. · 9.68 Impact Factor
