Piers R. Blackett

Type 2 Diabetes Genetics: Beyond GWAS

The global epidemic of type 2 diabetes mellitus (T2D) is one of the most challenging problems of the 21(st) century leading cause of and the fifth death worldwide. Substantial evidence suggests that T2D is a multifactorial disease with a strong genetic component. Recent genome-wide association studies (GWAS) have successfully identified and replicated nearly 75 susceptibility loci associated with T2D and related metabolic traits, mostly in Europeans, and some in African, and South Asian populations. The GWAS serve as a starting point for future genetic and functional studies since the mechanisms of action by which these associated loci influence disease is still unclear and it is difficult to predict potential implication of these findings in clinical settings. Despite extensive replication, no study has unequivocally demonstrated their clinical role in the disease management beyond progression to T2D from impaired glucose tolerance. However, these studies are revealing new molecular pathways underlying diabetes etiology, gene-environment interactions, epigenetic modifications, and gene function. This review highlights evolving progress made in the rapidly moving field of T2D genetics that is starting to unravel the pathophysiology of a complex phenotype and has potential to show clinical relevance in the near future.

Vascular health in children and adolescents: effects of obesity and diabetes

The foundations for cardiovascular disease in adults are laid in childhood and accelerated by the presence of comorbid conditions, such as obesity, diabetes, hypertension, and dyslipidemia. Early detection of vascular dysfunction is an important clinical objective to identify those at risk for subsequent cardiovascular morbidity and events, and to initiate behavioral and medical interventions to reduce risk. Typically, cardiovascular screening is recommended for young adults, especially in people with a family history of cardiovascular conditions. Children and adolescents were once considered to be at low risk, but with the growing health concerns related to sedentary lifestyle, poor diet and obesity, cardiovascular screening may be needed earlier so that interventions to improve cardiovascular health can be initiated. This review describes comorbid conditions that increase cardiovascular risk in youth, namely obesity and diabetes, and describes noninvasive methods to objectively detect vascular disease and quantify vascular function and structure through measurements of endothelial function, arterial compliance, and intima-media thickness. Additionally, current strategies directed toward prevention of vascular disease in these populations, including exercise, dietary interventions and pharmacological therapy are described.

Partial Defect in the Cholesterol Side-Chain Cleavage Enzyme P450scc (CYP11A1) Resembling Nonclassic Congenital Lipoid Adrenal Hyperplasia

CONTEXT The cholesterol side-chain cleavage enzyme (P450scc), encoded by the CYP11A1 gene, converts cholesterol to pregnenolone to initiate steroidogenesis. Genetic defects in P450scc cause a rare autosomal recessive disorder that is clinically indistinguishable from congenital lipoid adrenal hyperplasia (lipoid CAH). Nonclassic lipoid CAH is a recently recognized disorder caused by mutations in the steroidogenic acute regulatory protein (StAR) that retain partial function. OBJECTIVE We describe two siblings with hormonal findings suggesting nonclassic lipoid CAH, who had a P450scc mutation that retains partial function. PATIENTS AND METHODS A 46,XY male presented with underdeveloped genitalia and partial adrenal insufficiency; his 46,XX sister presented with adrenal insufficiency. Hormonal studies suggested nonclassic lipoid CAH. Sequencing of the StAR gene was normal, but compound heterozygous mutations were found in the CYP11A1 gene. Mutations were recreated in the F2 plasmid expressing a fusion protein of the cholesterol side-chain cleavage system. P450scc activity was measured as Vmax/Km for pregnenolone production in transfected COS-1 cells. RESULTS The patients were compound heterozygous for the previously described frameshift mutation 835delA and the novel missense mutation A269V. When expressed in the P450scc moiety of F2, the A269V mutant retained 11% activity of the wild-type F2 protein. CONCLUSIONS There is a broad clinical spectrum of P450scc deficiency. Partial loss-of-function CYP11A1 mutation can present with a hormonal phenotype indistinguishable from nonclassic lipoid CAH.

Insulin Pump Treatment for Recurrent Ketoacidosis in Adolescence

Moreover, two different female patients (cases 2 and 10) who once had palpitations when they consumed alcohol noticed the disappearance of the symptom after taking coenzyme Q10, which has a therapeutic effect on mitochondrial abnormality (3). Thus, these clinical pictures suggest that alcohol may be unpleasant toxin for DM-Mt3243 patients and that improved mitochondrial function may ameliorate the unpleasant alcohol effect. The fact that alcohol plays a role in the phenotypic expression of the 3460 or 14484 mitochondrial DNA mutation in Lebers hereditary optic neuropathy may further support our finding (4,5). Because mitochondria is an organella possessing aldehyde dehydrogenase, which is a key enzyme for aldehyde metabolism, and because supply of nicotinamide adenine dinucleotide, a cofactor of ethanol oxidation, is dependent on the mitochondrial membraneous system, alcohol intolerance concomitant with aldehyde accumulation or with change of redox state in liver may be understandable in groups of mitochondrial diseases. In addition, because ethanol decreases cytochrome oxidase activity or protein synthesis in mitochondria, it is likely that mitochondrial function in DM-Mt3243 will easily fall into a vicious circle with ethanol toxicity.

Lipids and apolipoproteins in growth hormone-deficient children during treatment☆☆☆

The role of growth hormone (GH) in regulating the transport of plasma lipoproteins has not been clearly defined, but past studies suggest that GH may influence cholesterol levels. This protocol was designed to evaluate possible changes in lipid and apolipoprotein status in GH-deficient children and children with neurosecretory dysfunction (NS) before GH therapy and at intervals after GH therapy was started. Twenty children with classic GH deficiency were evaluated, and 28% were hyperlipidemic at the onset of the study. Seven children were evaluated in the NS group, and only one (14%) showed an elevated total cholesterol (TC) greater than 200 mg/dL. The mean TC for all the GH-deficient children was elevated above the normal range, but not for the NS group. The mean apolipoprotein (apo) C-III level and its heparin-precipitated fraction (HP) were also elevated in the GH-deficient group, but only the apo C-III HP was elevated in the NS group. A standard replacement dose of recombinant methionyl GH was used, and therapy had no significant effect on TC or triglyceride (TG) levels. Apo C-III HP, a marker of hypertriglyceridemia, increased after the start of therapy, but no other lipoprotein levels changed significantly in the GH-deficient group. No changes were seen with treatment in the NS group. The longitudinal design of this study allowed demonstration of the later changes in the apolipoproteins and the presence of a distinct subset of patients with both GH deficiency and hypercholesterolemia. This study supports the role of GH in modulating lipid metabolism.

Two new unrelated cases of hereditary 1,25-dihydroxyvitamin D-resistant rickets with alopecia resulting from the same novel nonsense mutation in the vitamin D receptor gene.

ABSTRACT 1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) an important regulator of bone homeostasis, mediates its actions by binding to the vitamin D receptor (VDR), a nuclear transcription factor. Mutations in the VDR cause the rare genetic disease hereditary vitamin D resistant rickets (HVDRR). In this study, we examined two unrelated young female patients who exhibited severe early onset rickets, hypocalcemia, and hypophosphatemia. Both patients had partial alopecia but with different unusual patterns of scant hair. Sequencing of the VDR gene showed that both patients harbored the same unique nonsense mutation that resulted in a premature stop codon (R50X). Skin fibroblasts from patient #1 were devoid of VDR protein and 1,25(OH)2D3 treatment of these cells failed to induce CYP24A1 gene expression, a marker of 1,25(OH)2D3 action. In conclusion, we identified a novel nonsense mutation in the VDR gene in two patients with HVDRR and alopecia. The mutation truncates the VDR protein and causes 1,25(OH)2D3 resistance.

Ring chromosome 9 [r(9)(p24q34)]: A report of two cases

We report clinical and molecular cytogenetic studies in two patients with ring chromosome 9. Cytogenetics and fluorescent in situ hybridization (FISH) analysis using the p16 gene probe on 9p21, the ABL gene on 9q34, chromosome 9 alpha satellite‐centromeric probes, and TelVision 9p and 9q probes which identify subtelomere‐specific sequences on chromosome 9p and 9q, revealed 46,XX,r(9)(p24q34).ish r(9)(305J7‐T7‐,p16+,ABL+, D9S325−) and 46XY,r(9)(p24q34).ish r(9)(305J7‐T7‐,p16+,ABL+, D9S325−). Based on FISH analysis at least 115 kb was deleted on terminal 9p, and at least 95 kb from terminal 9q. In comparison with other reports of r(9), deletion 9p, and deletion 9q, both patients had clinical characteristics of ring 9 and additional features of deletion 9q or deletion 9p syndrome. The variability between the two cases with r(9) despite similar breakpoints identified by GTG‐banding and FISH may be explained by submicroscopic differences between deletion breakpoints, ring instability, interaction of other genes on the phenotype, and variation in fetal environmental conditions.

Studies on serum apolipoproteins and lipids in amniotic fluid and neonatal urine.

Amniotic fluid and neonatal urine were examined for the presence of lipids and serum apolipoproteins. Human apolipoproteins A-I, A-II, and ApoD found principally in serum high density lipoproteins were identified in both neonatal urine and amniotic fluid. A lecithin/sphingomyelin ratio of greater than 5 associated with fetal lung maturity was accompanied by the disappearance of A-II from amniotic fluid. Dissimilarities of total fatty acid composition of amniotic fluid when compared to cord serum or neonatal urine indicate other tissue sources for fatty acids found in amniotic fluid. In addition, the presence of serum apolipoproteins and lipids in both amniotic fluid and neonatal urine suggests that a least a portion of these constituents could be derived from fetal urine.

Lipoprotein abnormalities in compound heterozygous lipoprotein lipase deficiency after treatment with a low-fat diet and orlistat

BACKGROUND The treatment of familial hyperchylomicronemia presenting in early childhood with episodes of pancreatitis has been ineffective, and affected patients remain at risk for pancreatitis. OBJECTIVE To report on the effect of orlistat in siblings with severe inherited hyperchylomicronemia and to assess posttreatment lipoprotein concentrations and composition. METHODS Serial observations of plasma lipid levels and hospitalizations after treatment with orlistat and lipoprotein studies on a single fasting posttreatment sample. RESULTS The affected siblings inherited a lipoprotein lipase gene mutation from each of their parents: a novel mutation from their father (c.542G > C, p.G181R) and a known missense mutation from their mother (c.644G > A, p.G215E). When the boy presented to us at age 9 years of age and his sister at age 7 years, we found that addition of orlistat, a pancreatic lipase inhibitor, at a dose of 120 mg given before three low-fat meals a day was effective in reducing episodes of pancreatitis in the boy and in maintaining the triglyceride at lower levels in both children. During treatment, the children were observed to have elevations in apolipoprotein (apo)B, low-density lipoprotein particle concentration, abnormal apoB-containing subclasses, and deficiencies in apoA-I and apoA-II-containing lipoproteins, changes consistent with continuing increased cardiovascular risk. CONCLUSION The data support the need for more effective long-term treatments that not only prevent pancreatitis but also offset cardiovascular risk. Orlistat can be considered effective in augmenting the effect of a low-fat diet and reducing risk for pancreatitis.

Sex differences in cardiovascular disease risk in adolescents with type 1 diabetes.

BACKGROUND Cardiovascular disease is seen at a younger age and at a higher prevalence in patients with type 1 diabetes than in the general population. It is well described that women with type 1 diabetes have a higher relative risk of cardiovascular disease than men with type 1 diabetes, unlike that seen in the general population. The pathophysiology behind this is unknown. OBJECTIVE We performed a cross-sectional study to examine sex differences in cardiovascular disease risk factors in adolescents with type 1 diabetes between ages 13 and 20 years, compared with children of a similar age without type 1 diabetes. METHODS All patients underwent a dual energy x-ray absorptiometry scan to measure body composition and a pulse wave test measure of arterial elasticity. Fasting serum lipid levels, apolipoprotein B, and apolipoprotein C-III levels were measured in each patient. Twenty-nine children with type 1 diabetes (10 girls, 19 boys) and 37 healthy children (18 girls, 19 boys) participated. RESULTS Although no sex differences for body mass index (P = 0.91) and glycosylated hemoglobin (P = 0.69) were seen, girls with type 1 diabetes had a significantly higher percent trunk fat compared with boys (P = 0.004). No sex differences were found (P > 0.05) for percent trunk fat in adolescents without diabetes. There was no sex difference among any other cardiovascular risk factors in either children with or without diabetes. CONCLUSIONS Female adolescents with type 1 diabetes have more centrally distributed fat, which may contribute to their relatively higher cardiovascular disease risk. Attenuation of the central distribution of fat through exercise and dietary modifications may help ameliorate their subsequent cardiovascular disease burden.