Cramer Christensen

Loss-of-function mutations in SLC30A8 protect against type 2 diabetes

Loss-of-function mutations protective against human disease provide in vivo validation of therapeutic targets, but none have yet been described for type 2 diabetes (T2D). Through sequencing or genotyping of ∼150,000 individuals across 5 ancestry groups, we identified 12 rare protein-truncating variants in SLC30A8, which encodes an islet zinc transporter (ZnT8) and harbors a common variant (p.Trp325Arg) associated with T2D risk and glucose and proinsulin levels. Collectively, carriers of protein-truncating variants had 65% reduced T2D risk (P = 1.7 × 10−6), and non-diabetic Icelandic carriers of a frameshift variant (p.Lys34Serfs*50) demonstrated reduced glucose levels (−0.17 s.d., P = 4.6 × 10−4). The two most common protein-truncating variants (p.Arg138* and p.Lys34Serfs*50) individually associate with T2D protection and encode unstable ZnT8 proteins. Previous functional study of SLC30A8 suggested that reduced zinc transport increases T2D risk, and phenotypic heterogeneity was observed in mouse Slc30a8 knockouts. In contrast, loss-of-function mutations in humans provide strong evidence that SLC30A8 haploinsufficiency protects against T2D, suggesting ZnT8 inhibition as a therapeutic strategy in T2D prevention.

Identification of low-frequency and rare sequence variants associated with elevated or reduced risk of type 2 diabetes.

Through whole-genome sequencing of 2,630 Icelanders and imputation into 11,114 Icelandic cases and 267,140 controls followed by testing in Danish and Iranian samples, we discovered 4 previously unreported variants affecting risk of type 2 diabetes (T2D). A low-frequency (1.47%) variant in intron 1 of CCND2, rs76895963[G], reduces risk of T2D by half (odds ratio (OR) = 0.53, P = 5.0 × 10−21) and is correlated with increased CCND2 expression. Notably, this variant is also associated with both greater height and higher body mass index (1.17 cm per allele, P = 5.5 × 10−12 and 0.56 kg/m2 per allele, P = 6.5 × 10−7, respectively). In addition, two missense variants in PAM, encoding p.Asp563Gly (frequency of 4.98%) and p.Ser539Trp (frequency of 0.65%), confer moderately higher risk of T2D (OR = 1.23, P = 3.9 × 10−10 and OR = 1.47, P = 1.7 × 10−5, respectively), and a rare (0.20%) frameshift variant in PDX1, encoding p.Gly218Alafs*12, associates with high risk of T2D (OR = 2.27, P = 7.3 × 10−7).

Association of 24-h cardiac parasympathetic activity and degree of nephropathy in IDDM patients

In insulin-dependent diabetic patients, nephropathy is a predictor of mortality and coronary heart disease. Impaired cardiac vagal function is an important factor in the pathophysiology of sudden cardiac death in coronary heart disease. Autonomic neuropathy in diabetes in particular involves vagal function. Bedside tests and 24-h measurements of cardiac parasympathetic activity were compared in 37 insulin-dependent diabetic patients, and the relationship between 24-h vagal activity and degree of nephropathy was investigated. Nephropathy was classified according to urinary albumin excretion as normoalbuminuria, incipient, and overt nephropathy. Mean age (∼ 30 yr) was not different among groups. The 24-h measurements of parasympathetic activity appeared more sensitive than bedside tests, as 33% of patients without cardiac autonomic neuropathy in bedside tests had 24-h vagal activity values below the 95% confidence limits of 14 healthy control subjects. Patients with incipient or overt nephropathy had significantly lower mean values for vagal activity during both wake and sleep time than healthy control subjects. Increasing degree of nephropathy was associated significantly with increasing attenuation of 24-h vagal activity (P < 0.001). The covariation of degree of neuropathy and nephropathy may suggest common pathogenetic mechanisms. The reduced 24-h vagal activity, even in the early stages of nephropathy, could be an important risk factor for cardiac death in insulin-dependent diabetic patients.

Autonomic and Somatosensory Nerve Function After 2 Years of Continuous Subcutaneous Insulin Infusion in Type I Diabetes

Autonomic and somatosensory nerve function was studied in 24 insulin-dependent diabetic subjects (aged 29 ± 7 yrs, diabetes duration 8 ± 4 yr) randomly allocated to either continuous subcutaneous insulin infusion (CSII; n = 12) or unchanged conventional insulin therapy (CIT; n = 12). Measures of glycemic control and somatosensory and autonomic nerve function were comparable in the two groups at the start. Glycemic control was significantly improved in the CSII group throughout study, whereas it remained unchanged in the CIT group. In the CIT group, vibratory perception threshold (VPT) of the great toe and the medial malleolus deteriorated, as did heart rate variation (HRV) at rest, at deep breathing (.05 < P < .06), and at standing. In contrast, CSII patients retained their VPT and HRV. Comparison of nerve function alterations during the 2-yr trial showed better preservation in CSII than in CIT patients of VPT in the great toe (0.8 ± 1.7 vs. −1.4 ± 1.9 V, P < .01) and the medial malleolus (1.5 ± 2.9 vs. −1.4 ± 1.8 V, P < .05) and of HRV at rest (10 ± 24 vs. −13 ± 22 ms, P < .05) and at standing (−0.01 ± 0.13 vs. −0.15 ± 0.16 ms, P < .05). We conclude that intensified glycemic control can favorably influence parasympathetic and somatosensory nerve function in insulin-dependent diabetes mellitus.

Renal effects of acute calcium blockade with nifedipine in hypertensive patients receiving beta‐adrenoceptor‐blocking drugs

The effects on blood pressure and renal function of a single 20‐mg sublingual dose of nifedipine were investigated in 10 patients with mild to moderate arterial hypertension insufficiently treated on beta‐blocker monotherapy. Nifedipine induced a prompt and marked reduction of both systolic and diastolic blood pressure (average maximal reduction 30/22 mm Hg, P < 0.001). Despite the beta blockade, heart rate rose 25%. Only insignificant increments of glomerular filtration rate and renal plasma flow were registered, whereas calculated renal vascular resistance (RVR) was markedly reduced (P < 0.001). Urinary excretion rate of albumin and beta‐2 microglobulin rose after nifedipine, reflecting changes in glomerular as well as tubular function. Mean blood pressure seemed to be a major determinant of the excretion of proteins. There was a marked increase in the excretion of sodium after nifedipine and urine volume rose from a mean of 8.2 ± 1.3 to 12.5 ± 1.8 ml/min (P <0.01). The changes in sodium excretion rate correlated with the renal hemodynamic changes. Uric acid excretion rate rose remarkably after nifedipine and the magnitude of the changes seemed intimately related to the basal level of RVR. The results indicate that nifedipine therapy may be advantageous in patients whose hypertension is insufficiently controlled with beta blockers alone. Renal blood flow is maintained and there is a desirable diuretic action and enhancement of uric acid excretion.

Renal Factors Influencing Blood Pressure Threshold and Choice of Treatment for Hypertension in IDDM

In this article, we analyze the blood pressure (BP) threshold for the start of antihypertensive treatment in insulin-dependent diabetes mellitus (IDDM) patients, with particular emphasis on those with persistent microalbuminuria or proteinuria (incipient and overt nephropathy, respectively). In such individuals, there is a clear increase in the prevalence of hypertension and in actual measured BP values that is not observed in normoalbuminuric patients. In 94 young healthy adults (<45 yr of age), average mean ± SD arterial pressure (MAP; diastolic + 1/3 pulse pressure) was ∼90.0 ± 8.1 mmHg, closely corresponding to large population studies. In microalbuminuric IDDM patients, MAP values between ∼105 and ∼95 mmHg have been found in different studies, and the level has progressively decreased in various studies between 1984 and 1990 with similar BP-measuring techniques. Somewhat higher values are seen in patients with proteinuria, who are also consistently characterized by reduced glomerular filtration rate (GFR). A clear correlation is found between MAP plotted against the increased rate of microalbuminuria (%/yr) in incipient nephropathy and against fall rate of GFR (ml · min−1 · mo−1) in proteinuric patients. In the natural history of renal disease, different cutoff points in MAP for start of progression are observed: >95 mmHg for the start of progression of microalbuminuria and >105 mmHg for the decrease in GFR. During antihypertensive treatment, there is reduction or no progression in microalbuminuria with MAP of ∼90−95 mmHg and only a limited fall in GFR with MAP of ∼100 mmHg. However, certain antihypertensive drugs (angiotensin-converting enzyme inhibitors) may have specific renoprotective actions, reducing microalbuminuria at rather low BP levels or even independent of BP reduction. The optimal way of monitoring BP may be by 24-h ambulatory recording.

Long-term therapy of arterial hypertension with nifedipine given alone or in combination with a beta-adrenoceptor blocking agent.

SummaryThe antihypertensive effect of nifedipine during long-term therapy was investigated in 5 patients receiving nifedipine as the sole drug and in 10 patients who had nifedipine in combination with a beta-adrenoceptor blocking drug. Nifedipine monotherapy was problematic because of side-effects and development of resistance to therapy after a few months. In patients who received the combined therapy significant and stable blood pressure reductions were maintained during the whole observation period (12–33 months). However, the occurrence of peripheral oedema in 4 of the patients necessitated the addition of a thiazide diuretic. It is concluded that nifedipine is not a first choice drug for the long-term treatment of arterial hypertension. When given in addition to a beta-blocker it is well tolerated and powerful but fluid retention may occur and if not counteracted by a diuretic it will limit the antihypertensive potential of the drug.

Identification and Functional Characterization of G6PC2 Coding Variants Influencing Glycemic Traits Define an Effector Transcript at the G6PC2-ABCB11 Locus

Genome wide association studies (GWAS) for fasting glucose (FG) and insulin (FI) have identified common variant signals which explain 4.8% and 1.2% of trait variance, respectively. It is hypothesized that low-frequency and rare variants could contribute substantially to unexplained genetic variance. To test this, we analyzed exome-array data from up to 33,231 non-diabetic individuals of European ancestry. We found exome-wide significant (P<5×10-7) evidence for two loci not previously highlighted by common variant GWAS: GLP1R (p.Ala316Thr, minor allele frequency (MAF)=1.5%) influencing FG levels, and URB2 (p.Glu594Val, MAF = 0.1%) influencing FI levels. Coding variant associations can highlight potential effector genes at (non-coding) GWAS signals. At the G6PC2/ABCB11 locus, we identified multiple coding variants in G6PC2 (p.Val219Leu, p.His177Tyr, and p.Tyr207Ser) influencing FG levels, conditionally independent of each other and the non-coding GWAS signal. In vitro assays demonstrate that these associated coding alleles result in reduced protein abundance via proteasomal degradation, establishing G6PC2 as an effector gene at this locus. Reconciliation of single-variant associations and functional effects was only possible when haplotype phase was considered. In contrast to earlier reports suggesting that, paradoxically, glucose-raising alleles at this locus are protective against type 2 diabetes (T2D), the p.Val219Leu G6PC2 variant displayed a modest but directionally consistent association with T2D risk. Coding variant associations for glycemic traits in GWAS signals highlight PCSK1, RREB1, and ZHX3 as likely effector transcripts. These coding variant association signals do not have a major impact on the trait variance explained, but they do provide valuable biological insights.

Genome-wide association studies in the Japanese population identify seven novel loci for type 2 diabetes

Genome-wide association studies (GWAS) have identified more than 80 susceptibility loci for type 2 diabetes (T2D), but most of its heritability still remains to be elucidated. In this study, we conducted a meta-analysis of GWAS for T2D in the Japanese population. Combined data from discovery and subsequent validation analyses (23,399 T2D cases and 31,722 controls) identify 7 new loci with genome-wide significance (P<5 × 10−8), rs1116357 near CCDC85A, rs147538848 in FAM60A, rs1575972 near DMRTA1, rs9309245 near ASB3, rs67156297 near ATP8B2, rs7107784 near MIR4686 and rs67839313 near INAFM2. Of these, the association of 4 loci with T2D is replicated in multi-ethnic populations other than Japanese (up to 65,936 T2Ds and 158,030 controls, P<0.007). These results indicate that expansion of single ethnic GWAS is still useful to identify novel susceptibility loci to complex traits not only for ethnicity-specific loci but also for common loci across different ethnicities.

Increased blood pressure in diabetes: essential hypertension or diabetic nephropathy?

This study was performed to evaluate whether it is possible to distinguish between diabetics with essential hypertension and diabetics with elevated blood pressure due to diabetic nephropathy. We investigated 46 young diabetics, 21 having incipient nephropathy defined as urinary albumin excretion (UAE) persistently above 15 micrograms/min and total urinary protein less than 0.5 g per 24 h, and 25 patients having overt nephropathy with total protein excretion equal to or above 0.5 g per 24 h. Twenty-three patients with essential hypertension were also studied as well as 24 healthy controls. Only males and females between the age of 25 years and 40 years were included. We found a positive correlation between UAE and blood pressure (BP) but a considerable overlap in BP and UAE values between diabetics and patients with essential hypertension. However, plotting urinary albumin excretion against BP, diabetics and non-diabetics with essential hypertension could be nearly totally separated. Comparison at a similar blood pressure level, for example, mean arterial blood pressure of 125 mmHg, shows that diabetics have UAE 100 times higher than non-diabetic essential hypertensives. Conversely, UAE of 100 micrograms/min would imply that mean arterial blood pressure is about 70 mmHg higher in the non-diabetic essential hypertensives than in the diabetics. Five diabetics with normal UAE and elevated blood pressure higher or equal to 160/95 mmHg were clearly within the area of the essential hypertensive patients. Our observations indicate that it seems possible to distinguish diabetic patients with essential hypertension from diabetics with elevated blood pressure due to early or advanced nephropathy.