Genetic Discrimination Between LADA and Childhood-Onset Type 1 Diabetes Within the MHC.

OBJECTIVE: The MHC region harbors the strongest loci for latent autoimmune diabetes in adults (LADA); however, the strength of association is likely attenuated compared with that for childhood-onset type 1 diabetes. In this study, we recapitulate independent effects in the MHC class I region in a population with type 1 diabetes and then determine whether such conditioning in LADA yields potential genetic discriminators between the two subtypes within this region. RESEARCH DESIGN AND METHODS: Chromosome 6 was imputed using SNP2HLA, with conditional analysis performed in type 1 diabetes case subjects (n = 1,985) and control subjects (n = 2,219). The same approach was applied to a LADA cohort (n = 1,428) using population-based control subjects (n = 2,850) and in a separate replication cohort (656 type 1 diabetes case, 823 LADA case, and 3,218 control subjects). RESULTS: The strongest associations in the MHC class II region (rs3957146, ß [SE] = 1.44 [0.05]), as well as the independent effect of MHC class I genes, on type 1 diabetes risk, particularly HLA-B*39 (ß [SE] = 1.36 [0.17]), were confirmed. The conditional analysis in LADA versus control subjects showed significant association in the MHC class II region (rs3957146, ß [SE] = 1.14 [0.06]); however, we did not observe significant independent effects of MHC class I alleles in LADA. CONCLUSIONS: In LADA, the independent effects of MHC class I observed in type 1 diabetes were not observed after conditioning on the leading MHC class II associations, suggesting that the MHC class I association may be a genetic discriminator between LADA and childhood-onset type 1 diabetes.

First Genome-Wide Association Study of Latent Autoimmune Diabetes in Adults Reveals Novel Insights Linking Immune and Metabolic Diabetes.

OBJECTIVE: Latent autoimmune diabetes in adults (LADA) shares clinical features with both type 1 and type 2 diabetes; however, there is ongoing debate regarding the precise definition of LADA. Understanding its genetic basis is one potential strategy to gain insight into appropriate classification of this diabetes subtype. RESEARCH DESIGN AND METHODS: We performed the first genome-wide association study of LADA in case subjects of European ancestry versus population control subjects (n = 2,634 vs. 5,947) and compared against both case subjects with type 1 diabetes (n = 2,454 vs. 968) and type 2 diabetes (n = 2,779 vs. 10,396). RESULTS: The leading genetic signals were principally shared with type 1 diabetes, although we observed positive genetic correlations genome-wide with both type 1 and type 2 diabetes. Additionally, we observed a novel independent signal at the known type 1 diabetes locus harboring PFKFB3, encoding a regulator of glycolysis and insulin signaling in type 2 diabetes and inflammation and autophagy in autoimmune disease, as well as an attenuation of key type 1-associated HLA haplotype frequencies in LADA, suggesting that these are factors that distinguish childhood-onset type 1 diabetes from adult autoimmune diabetes. CONCLUSIONS: Our results support the need for further investigations of the genetic factors that distinguish forms of autoimmune diabetes as well as more precise classification strategies.

Linkage Analysis of Genomic Regions Contributing to the Expression of Type 1 Diabetes Microvascular Complications and Interaction with HLA.

We conducted linkage analysis to follow up earlier work on microvascular complications of type 1 diabetes (T1D). We analyzed 415 families (2,008 individuals) previously genotyped for 402 SNP markers spanning chromosome 6. We did linkage analysis for the phenotypes of retinopathy and nephropathy. For retinopathy, two linkage peaks were mapped: one located at the HLA region and another novel locus telomeric to HLA. For nephropathy, a linkage peak centromeric to HLA was mapped, but the linkage peak telomeric to HLA seen in retinopathy was absent. Because of the strong association of T1D with DRB1*03:01 and DRB1*04:01, we stratified our analyses based on families whose probands were positive for DRB1*03:01 or DRB1*04:01. When analyzing the DRB1*03:01-positive retinopathy families, in addition to the novel telomeric locus, one centromeric to HLA was identified at the same location as the nephropathy peak. When we stratified on DRB1*04:01-positive families, the HLA telomeric peak strengthened but the centromeric peak disappeared. Our findings showed that HLA and non-HLA loci on chromosome 6 are involved in T1D complications' expression. While the HLA region is a major contributor to the expression of T1D, our results suggest an interaction between specific HLA alleles and other loci that influence complications' expression.

Familial risk factors for microvascular complications and differential male-female risk in a large cohort of American families with type 1 diabetes.

CONTEXT: Type 1 diabetes (T1D) complications are responsible for much of the disease morbidity. Evidence suggests that familial factors exert an influence on susceptibility to complications. OBJECTIVES: We investigated familial risk factors and gender differences for retinopathy, nephropathy, and neuropathy. DESIGN AND SETTING: This study was a case-control design nested on a cohort of T1D families. We collected data (questionnaire, medical records) starting in 1988. Follow-up has been ongoing since 2004. PATIENTS: There were 8114 T1D patients among 6707 families. All patients had T1D onset age younger than 30 yr and required insulin treatment. Patients who remained without a complication after more than 15 yr of diabetes were considered to be without that complication for our analyses. RESULTS: A complication in a sibling increased the risk for that complication among probands: odds ratio 9.9 (P < 0.001) for retinopathy, 6.2 for nephropathy (P < 0.001), and 2.2 for neuropathy (P < 0.05). Compared with male probands, a female T1D proband had 1.7-fold higher retinopathy risk (P < 0.001) and 2-fold higher neuropathy risk (P < 0.001). T1D cases with onset between ages 5 and 14 yr had an increased complications risk compared with subjects diagnosed either at a very young age or after puberty. The presence of one complication significantly increased the risk for others. If a parent had type 2 diabetes, the risk for nephropathy increased (odds ratio 1.9, P < 0.01, but T1D in a parent did not increase the risk). CONCLUSIONS: We confirmed that familial factors influence T1D microvascular pathologies, suggesting a shared genetic basis for complications, perhaps independent of T1D susceptibility. We also found an unexpected increased female risk for complications.

Crystal structure and substrate specificity of the beta-ketoacyl-acyl carrier protein synthase III (FabH) from Staphylococcus aureus.

beta-Ketoacyl-ACP synthase III (FabH), an essential enzyme for bacterial viability, catalyzes the initiation of fatty acid elongation by condensing malonyl-ACP with acetyl-CoA. We have determined the crystal structure of FabH from Staphylococcus aureus, a Gram-positive human pathogen, to 2 A resolution. Although the overall structure of S. aureus FabH is similar to that of Escherichia coli FabH, the primer binding pocket in S. aureus FabH is significantly larger than that present in E. coli FabH. The structural differences, which agree with kinetic parameters, provide explanation for the observed varying substrate specificity for E. coli and S. aureus FabH. The rank order of activity of S. aureus FabH with various acyl-CoA primers was as follows: isobutyryl- > hexanoyl- > butyryl- > isovaleryl- >> acetyl-CoA. The availability of crystal structure may aid in designing potent, selective inhibitors of S. aureus FabH.

Inhibitors of type II NADH:menaquinone oxidoreductase represent a class of antitubercular drugs.

Mycobacterium tuberculosis (Mtb) is an obligate aerobe that is capable of long-term persistence under conditions of low oxygen tension. Analysis of the Mtb genome predicts the existence of a branched aerobic respiratory chain terminating in a cytochrome bd system and a cytochrome aa(3) system. Both chains can be initiated with type II NADH:menaquinone oxidoreductase. We present a detailed biochemical characterization of the aerobic respiratory chains from Mtb and show that phenothiazine analogs specifically inhibit NADH:menaquinone oxidoreductase activity. The emergence of drug-resistant strains of Mtb has prompted a search for antimycobacterial agents. Several phenothiazines analogs are highly tuberculocidal in vitro, suppress Mtb growth in a mouse model of acute infection, and represent lead compounds that may give rise to a class of selective antibiotics.

Bacterial beta-ketoacyl-acyl carrier protein synthases as targets for antibacterial agents.

As a result of increasing drug resistance in pathogenic bacteria, there is a critical need for novel broad-spectrum antibacterial agents. As fatty acid synthesis (FAS) in bacteria is an essential process for cell survival, the enzymes involved in the FAS pathway have emerged as promising targets for antimicrobial agents. Several lines of evidence have indicated that bacterial condensing enzymes are central to the initiation and elongation steps in bacterial fatty acid synthesis and play a pivotal role in the regulation of the entire fatty acid synthesis pathway. beta-ketoacyl-acyl carrier protein (ACP) synthases (KAS) from various bacterial species have been cloned, expressed and purified in large quantities for detailed enzymological, structural and screening studies. Availability of purified KAS from a variety of bacteria, along with a combination of techniques, including combinatorial chemistry, high-throughput screening, and rational drug design based on crystal structures, will undoubtedly aid in the discovery and development of much needed potent and broad-spectrum antibacterial agents. In this review we summarize the biochemical, biophysical and inhibition properties of beta-ketoacyl-ACP synthases from a variety of bacterial species.

First X-ray cocrystal structure of a bacterial FabH condensing enzyme and a small molecule inhibitor achieved using rational design and homology modeling.

The first cocrystal structure of a bacterial FabH condensing enzyme and a small molecule inhibitor is reported. The inhibitor was obtained by rational modification of a high throughput screening lead with the aid of a S. pneumoniae FabH homology model. This homology model was used to design analogues that would have both high affinity for the enzyme and appropriate aqueous solubility to facilitate cocrystallization studies.