Insulin resistance in African Americans

Genome-wide association study identifies novel loci association with fasting insulin and insulin resistance in African Americans

Insulin resistance (IR) is a key determinant of type 2 diabetes (T2D) and other metabolic disorders. This genome-wide association study (GWAS) was designed to shed light on the genetic basis of fasting insulin (FI) and IR in 927 non-diabetic African Americans. 5 396 838 single-nucleotide polymorphisms (SNPs) were tested for associations with FI or IR with adjustments for age, sex, body mass index, hypertension status and first two principal components. Genotyped SNPs (n = 12) with P < 5 × 10(-6) in African Americans were carried forward for de novo genotyping in 570 non-diabetic West Africans. We replicated SNPs in or near SC4MOL and TCERG1L in West Africans. The meta-analysis of 1497 African Americans and West Africans yielded genome-wide significant associations for SNPs in the SC4MOL gene: rs17046216 (P = 1.7 × 10(-8) and 2.9 × 10(-8) for FI and IR, respectively); and near the TCERG1L gene with rs7077836 as the top scoring (P = 7.5 × 10(-9) and 4.9 × 10(-10) for FI and IR, respectively). In silico replication in the MAGIC study (n = 37 037) showed weak but significant association (adjusted P-value of 0.0097) for rs34602777 in the MYO5A gene. In addition, we replicated previous GWAS findings for IR and FI in Europeans for GCKR, and for variants in four T2D loci (FTO, IRS1, KLF14 and PPARG) which exert their action via IR. In summary, variants in/near SC4MOL, and TCERG1L were associated with FI and IR in this cohort of African Americans and were replicated in West Africans. SC4MOL is under-expressed in an animal model of T2D and plays a key role in lipid biosynthesis, with implications for the regulation of energy metabolism, obesity and dyslipidemia. TCERG1L is associated with plasma adiponectin, a key modulator of obesity, inflammation, IR and diabetes.

Metabolic syndrome and mild to moderate chronic kidney disease among minorities

The incidence and prevalence of metabolic syndrome and chronic kidney disease (CKD) are increasing in the US population as a whole, but much more rapidly among ethnic minorities. Recent studies have shown that metabolic syndrome is an independent risk factor for the development of incident CKD in African Americans and American Indians distinct from its impact on cardiovascular and all-cause mortality. The pathogenesis of metabolic syndrome in ethnic minorities often is multifactorial. We review the myriad facets of the impact of the metabolic syndrome on the pathophysiology of CKD in minorities. In addition to classic biochemical and physiologic factors, increasing attention is being drawn to the major role of novel factors such as adiponectin and socioeconomic and cultural factors in the development of obesity and insulin resistance; an understudied area that may modulate clinically relevant consequences of biochemical and pathophysiologic aberrations. We present an integrated pathophysiologic viewpoint that incorporates insights from basic science, socioeconomic inquiry, and clinical studies into a framework for clinical practice and investigation.

Noninvasive assessment of target organ injury in children with the metabolic syndrome

The prevalence of overweight has increased sharply since the 1980s, with morbid obesity rising at an even higher rate. Comorbidities related to adiposity now consume almost 10% of all US health care dollars. Unfortunately, overweight children already demonstrate elevations in cardiovascular risk factors. These children are extremely likely to remain obese in adulthood and are likely to progress to diabetes and heart and kidney diseases. It is not surprising, therefore, that the diagnosis of the metabolic syndrome is being made with increasing frequency in American adolescents. The authors show that noninvasive methods are now available to measure target organ damage related to obesity and the metabolic syndrome in children. They explore the data linking the cardiovascular risk factors that cluster as the metabolic syndrome to early subclinical atherosclerotic change such as left ventricular hypertrophy, carotid intima-media thickness, vascular function abnormalities, and microalbuminuria. Evidence for the benefits of treatment and guidelines for the assessment for target organ damage in children are provided.

Maternal leptin concentrations are similar in African Americans and Caucasians in normal pregnancy, preeclampsia and small-for-gestational-age infants

Leptin concentrations were measured in African American women in order to assess leptin's role in the increased frequency and severity of preeclampsia. In addition, leptin concentrations were measured in women who delivered small-for-gestational-age (SGA) infants. A case-control study of African American and Caucasian women with normal pregnancies, preeclampsia, or SGA infants was done. Plasma leptin was quantitated by radio-immunoassay. The previously recognized pattern of increased leptin concentrations in preeclampsia was replicated. Leptin concentrations did not differ by race in any diagnostic category, and concentrations in women with SGA infants were not higher than those in healthy women. Differences in the frequency and severity of preeclampsia in African Americans cannot be explained by higher leptin concentrations.

Diabetes in African Americans

African Americans have a high risk for type 2 diabetes. Genetic traits, the prevalence of obesity, and insulin resistance all contribute to the risk of diabetes in the African American community. African Americans have a high rate of diabetic complications, because of poor glycaemic control and racial disparities in health care in the USA. African Americans with diabetes may have an atypical presentation that simulates type 1 diabetes, but then their subsequent clinical course is typical of type 2 diabetes. Culturally sensitive strategies, structured disease management protocols, and the assistance of nurses, diabetic educators, and other health care professionals are effective in improving the outcome of diabetes in the African American community.

Hypothesis: obesity and the insulin resistance syndrome play a major role in end-stage renal failure attributed to hypertension and labelled 'hypertensive nephrosclerosis'

About a third of new cases of renal failure in USA are attributed to hypertension despite controversy about the frequency and pathology of so called hypertensive nephrosclerosis. In spite of good documentation that obesity causes renal failure and in spite of the global epidemic of obesity this diagnosis does not feature on most renal failure registries. New documentation that progressive renal failure in hypertension is linked to insulin resistance and analysis of NHANES III data which shows a strong positive significant dose-response relationship between insulin resistance and chronic kidney disease strengthen the view that so called hypertensive nephrosclerosis may be linked more closely to obesity and insulin resistance than to blood pressure. The pathology of the kidney in hypertension has changed. Studies 50 years ago did not show segmental glomerulosclerosis, which has recently been shown to be the key lesion in hypertensive nephrosclerosis. Recent documentation that this is a major mechanism of progression in hypertension together with the fact that similar segmental glomerulosclerosis is the key lesion in obesity and the metabolic syndrome suggests that these factors are more important than hypertension in renal failure attributed to hypertensive nephrosclerosis.

Effects of antihypertensive drugs and gene variants in the renin-angiotensin system

Many genes and environmental factors are involved in the pathogenesis of hypertension, but the exact cause of essential hypertension has not yet been clarified. Gene polymorphism of the renin-angiotensin system (RAS) is one of the candidates. In the current study, we examined whether there was a correlation between the gene polymorphisms in RAS and either the choice of antihypertensive drugs or their efficacy. Subjects with essential hypertension (n=299) were recruited from among the outpatients of Osaka University Hospital and provided their informed consent for genetic analysis. Physicians freely chose the antihypertensive drugs and adjusted its dose until the patient's blood pressure was well controlled. The efficacy of each antihypertensive drug was estimated using the following formula: ABP=BP 1 (before treatment) - BP 2 (after treatment)/BP 1 x 100 (%). Gene variants in RAS were determined using PCR or PCR-RFLP (restriction fragment of polymorphism). The gene polymorphisms of RAS were not associated with delta SBP or ADBP. However, the mean ASBP in subjects with a deletion homozygote of the angiotensin converting enzyme gene (ACE/DD) was significantly lower (p<0.05) than that in patients with an insertion I allele of the ACE gene. The gene polymorphisms of RAS did not significantly affect the choice of antihypertensive drugs. Even though gene polymorphism in the renin angiotensin system was not a major factor in the antihypertensive therapy, the determination of genotype might be of help in the management of essential hypertension.