👤 Jen-Zen Chuang

Genome-wide association studies have identified over 150 loci associated with lipid traits, however, no large-scale studies exist for Hispanics and other minority populations. Additionally, the genetic architecture of lipid-influencing loci remains largely unknown. We performed one of the most racially/ethnically diverse fine-mapping genetic studies of HDL-C, LDL-C, and triglycerides to-date using SNPs on the MetaboChip array on 54,119 individuals: 21,304 African Americans, 19,829 Hispanic Americans, 12,456 Asians, and 530 American Indians. The majority of signals found in these groups generalize to European Americans. While we uncovered signals unique to racial/ethnic populations, we also observed systematically consistent lipid associations across these groups. In African Americans, we identified three novel signals associated with HDL-C (LPL, APOA5, LCAT) and two associated with LDL-C (ABCG8, DHODH). In addition, using this population, we refined the location for 16 out of the 58 known MetaboChip lipid loci. These results can guide tailored screening efforts, reveal population-specific responses to lipid-lowering medications, and aid in the development of new targeted drug therapies. Show less

Obesity is linked to type 2 diabetes (T2D) and cardiovascular diseases; however, the underlying molecular mechanisms remain unclear. We aimed to identify obesity-associated molecular features that may contribute to obesity-related diseases. Using circulating monocytes from 1,264 Multi-Ethnic Study of Atherosclerosis (MESA) participants, we quantified the transcriptome and epigenome. We discovered that alterations in a network of coexpressed cholesterol metabolism genes are a signature feature of obesity and inflammatory stress. This network included 11 BMI-associated genes related to sterol uptake (↑LDLR, ↓MYLIP), synthesis (↑SCD, FADS1, HMGCS1, FDFT1, SQLE, CYP51A1, SC4MOL), and efflux (↓ABCA1, ABCG1), producing a molecular profile expected to increase intracellular cholesterol. Importantly, these alterations were associated with T2D and coronary artery calcium (CAC), independent from cardiometabolic factors, including serum lipid profiles. This network mediated the associations between obesity and T2D/CAC. Several genes in the network harbored C-phosphorus-G dinucleotides (e.g., ABCG1/cg06500161), which overlapped Encyclopedia of DNA Elements (ENCODE)-annotated regulatory regions and had methylation profiles that mediated the associations between BMI/inflammation and expression of their cognate genes. Taken together with several lines of previous experimental evidence, these data suggest that alterations of the cholesterol metabolism gene network represent a molecular link between obesity/inflammation and T2D/CAC. Show less

Identification of genetic variants that influence bipolar I disorder (BPD-I) through genome-wide association (GWA) studies is limited in Asian populations. The current study aimed to identify novel common variants for BPD-I in an ethnically homogeneous Taiwanese sample using a multi-stage GWA study design. At the discovery stage, 200 BPD-I patients and 200 controls that combined to form 16 pools were genotyped with 1 million markers. Utilizing a newly developed rank-based method, top-ranked markers were selected. After validation with individual genotyping, a fine-mapping association study was conducted to identify associated loci using 240 patients and 240 controls. At the last stage, independent samples were collected (351 cases and 341 controls) for replication. Among the top-ranked markers from the discovery stage, eight genes and 15 individual SNPs were evaluated in the fine-mapping stage. At this stage, rs7619173, which is not in a gene coding region, showed the most significant association (P = 2 ∗ 10(-5)) with BPD-I. Four genes had empirical P-values<0.05, including KCNH7 (P = 0.0047), MYST4 (P = 0.0047), NRXN3 (P = 0.0095), and SEMA3D (P = 0.037). For markers genotyped in replication samples, rs7619173 exhibited a significant association (P(combined) = 2 ∗ 10(-4)) after multiple testing correction, while markers rs11001178 (MYST4) and rs2217887 (NRXN3) showed weak associations (P(combined) = 0.02) with BPD-I. A multi-stage GWA design has the potential to uncover the underlying pathogenesis of a complex trait. Findings in the present study highlight three loci that warrant further investigation for bipolar. Show less

17β-Hydroxysteroid dehydrogenase type-3 (17βHSD-3) deficiency is a rare cause of 46,XY disorders of sex development. The enzyme converts androstenedione to testosterone, necessary for masculinization of male genitalia in utero. 17βHSD-3 deficiency is frequently diagnosed late, at puberty, following virilization, with consequent female-to-male gender reassignment in 39-64%. The decision for sex of rearing is difficult, especially if diagnosed in early childhood. Consensus guidelines are equivocal or support male gender assignment. Long-term outcomes data to guide decisions are also lacking; however, in the few cases of early diagnosis and orchiectomy, female gender retention appears more likely.We report two patients with 17βHSD-3 deficiency, who presented at unusual ages, in whom female gender was chosen. We performed a focused literature review and summary of gender outcomes in 17βHSD-3 deficiency following early orchiectomy. Patient A was a phenotypic female who presented at one year of age with bilateral inguinal hernias and external female genitalia. Testes were identified at surgery. The karyotype was 46,XY. She was initially diagnosed with complete androgen insensitivity syndrome; however, androgen receptor mutation analysis was negative. Human chorionic gonadotropin stimulation yielded a low testosterone: androstenedione ratio (0.6, normal >0.8). Genetic testing demonstrated compound heterozygosity for two known mutations of the HSD17B3 gene. She underwent bilateral orchiectomy at two years of age.Patient B was born with female genitalia and virilized at 13 years of age. She did not seek evaluation until 22 years of age. Her karyotype was 46,XY. She had bilateral inguinal testes and low testosterone: androstenedione ratio (0.3). HSD17B3 gene sequencing showed her to be a compound heterozygote for two known mutations. She identified herself as female and underwent bilateral orchiectomy and estrogen replacement therapy. These two patients highlight the complexities of diagnosis and management in 17βHSD-3 deficiency. Although existing data are limited, early orchiectomy is likely to result in retention of female gender identity, avoiding the complications related to virilization in adolescence. As such, it is important to pursue a definitive diagnosis to guide clinical decisions, and to have the support and long term follow up with an inter-disciplinary disorders of sex development team. Show less

Apolipoprotein A-V (apo A-V) exerts a potent triglyceride (TG)-lowering effect through enhanced intravascular TG-hydrolysis with increased uptake of TG-derived free fatty acids into muscle and adipose tissue. Genetic variants in the APOA5 gene were strongly associated with plasma TG concentrations. The aim of this study was to examine whether APOA5 genetic variation was associated with obesity. We genotyped the missense c.553 G>T polymorphism (p.G185C) in the APOA5 gene in 1,085 Chinese (333 obese subjects and 752 nonobese controls). We analyzed the association between the c.553 G>T polymorphism and obesity and related metabolic phenotypes. The T allele at the c.553 G>T polymorphism was associated with higher plasma TG concentrations. Each additional T allele was associated with an increased TG concentration of 53.5 mg/dl (95% confidence interval (CI) 29.6-76.0, P < 0.0001). However, the T allele was associated lower risk of obesity (odds ratio (OR), 0.48; 95% CI 0.32-0.73, P = 0.0004). Each additional copy of the T allele was associated with a BMI decrease of 0.73 kg/m(2) (95% CI 0.26-1.16, P = 0.002), equivalent to 2.11 kg in a person 1.7 m tall. We may then conclude that the TG-raising APOA5 genetic variant was associated with a decrease in BMI and reduced risk of obesity in the Chinese population. Show less

The molecular mechanism involved in the hypertrophy of the orbital fat in patients with Graves' ophthalmopathy or thyroid eye disease (TED) remains unclear. Comparison of genome-wide expression profiles may help in the search for the gene sets involved in TED. Twenty-five orbital adipose tissue specimens were obtained, from which the RNA was isolated. Four of the tissue specimens (from four individuals, two with TED and two control subjects) were subjected to cDNA microarray analysis. The data were analyzed by the gene set enrichment analysis (GSEA) to survey the biological pathways involved in the pathogenesis of TED. Messenger RNA levels of some top-ranked genes in GSEA-selected pathways are validated by quantitative PCR (QPCR). The expression of specific gene sets related to lytic vacuoles, lysosomes, and vacuoles were different between the specimens obtained from patients with TED and control subjects (P < 0.001). These three gene sets overlapped. For QPCR, four top-ranked genes were selected from these overlapping gene sets and another one that related to visual failure, using 21 independent samples of patients with TED (n = 15) and control subjects (n = 6). The results showed that ceroid-lipofuscinosis, neuronal 2, late infantile (CLN2; P = 0.044) and ceroid-lipofuscinosis, neuronal 3, juvenile (CLN3, which related to visual failure; P = 0.012) were significantly downregulated in the orbital fat of patients with TED. The expression of the beta subunit of hexosaminidase A (HEXB) was reduced as well, but the change did not reach statistical significance (P = 0.058). Lysosome-related genes, such as CLN2, CLN3, and HEXB, may be involved in the pathogenesis of adipose tissue hypertrophy in TED. Show less

Glycogen synthase kinase 3 (GSK3) encodes a serine/threonine protein kinase, is known to play roles in many biological processes. Two closely related GSK3 isoforms encoded by distinct genes: GSK3alpha (51 kDa) and GSK3beta (47 kDa). In previously studies, most GSK3 inhibitors are not only inhibiting GSK3, but are also affecting many other kinases. In addition, because of highly similarity in amino acid sequence between GSK3alpha and GSK3beta, making it difficult to identify an inhibitor that can be selective against GSK3alpha or GSK3beta. Thus, it is relatively difficult to address the functions of GSK3 isoforms during embryogenesis. At this study, we attempt to specifically inhibit either GSK3alpha or GSK3beta and uncover the isoform-specific roles that GSK3 plays during cardiogenesis. We blocked gsk3alpha and gsk3beta translations by injection of morpholino antisense oligonucleotides (MO). Both gsk3alpha- and gsk3beta-MO-injected embryos displayed similar morphological defects, with a thin, string-like shaped heart and pericardial edema at 72 hours post-fertilization. However, when detailed analysis of the gsk3alpha- and gsk3beta-MO-induced heart defects, we found that the reduced number of cardiomyocytes in gsk3alpha morphants during the heart-ring stage was due to apoptosis. On the contrary, gsk3beta morphants did not exhibit significant apoptosis in the cardiomyocytes, and the heart developed normally during the heart-ring stage. Later, however, the heart positioning was severely disrupted in gsk3beta morphants. bmp4 expression in gsk3beta morphants was up-regulated and disrupted the asymmetry pattern in the heart. The cardiac valve defects in gsk3beta morphants were similar to those observed in axin1 and apcmcr mutants, suggesting that GSK3beta might play a role in cardiac valve development through the Wnt/beta-catenin pathway. Finally, the phenotypes of gsk3alpha mutant embryos cannot be rescued by gsk3beta mRNA, and vice versa, demonstrating that GSK3alpha and GSK3beta are not functionally redundant. We conclude that (1) GSK3alpha, but not GSK3beta, is necessary in cardiomyocyte survival; (2) the GSK3beta plays important roles in modulating the left-right asymmetry and affecting heart positioning; and (3) GSK3alpha and GSK3beta play distinct roles during zebrafish cardiogenesis. Show less

Multiple osteochondromatosis, also known as hereditary multiple exostoses (HME), is an inherited autosomal dominant disorder characterized by the presence of multiple exostoses on the long bones. These exostoses are benign cartilaginous tumors (enchondromata). Three different exostosis (EXT) loci on chromosomes 8q (exostosin 1, EXT1), 11p (exostosin 2, EXT2) and 19p (exostosin 3, EXT3) have been reported. Recently, the EXT1 and EXT2 genes were identified by positional cloning. Using polymerase chain reaction and direct sequencing, we analyzed the EXT1 and EXT2 genes in three familial cases and one sporadic case of HME in Taiwanese patients. We found three novel mutations (S277X in the EXT1 gene, and G194X and 939+1G>A in the EXT2 gene) and a known mutation (Q172X in the EXT2 gene). Mutation analysis in families with HME allows for genetic counseling and prenatal diagnosis. Show less

Apolipoprotein AV (APOA5) is an important determinant of plasma triglyceride concentration. This study aimed to investigate the relationship of an amino acid substitution at position 182 (G182C) of the apolipoprotein AV (APOA5) gene with triglyceride concentration in a Taiwanese population. This study enrolled two cohorts: non-diabetic subjects (112 males and 89 females) aged 50.3+/-11.0 years (mean+/-sd) and diabetic subjects (106 males and 96 females) aged 62.1+/-10.3 years. The relationship between the G182C polymorphism (rs 2075291) and plasma triglycerides was examined. Demographic and metabolic parameters including age, sex, body mass index, fasting plasma glucose and total cholesterol were also obtained. The G182C polymorphism was a determinant of plasma triglycerides in both non-diabetic (P=0.022) and diabetic (P=0.003) groups, independent of age, gender, fasting plasma glucose, body mass index and total cholesterol. In the diabetic group, this genetic polymorphism interacts significantly (P=0.032) with fasting plasma glucose concentration on plasma triglycerides after adjustment for age, sex, body mass index and total cholesterol. In conclusion, the G182C polymorphism of the APOA5 gene affects plasma triglycerides in both non-diabetic and diabetic populations. The observed interaction of gene and glycaemic control further indicates a multifactorial nature of clinical phenotypes in subjects with Type 2 diabetes. Show less

Alternation in lipid metabolism can affect both insulin sensitivity and beta-cell function. Apolipoprotein A5 (APOA5) is an important determinant of lipid metabolism. The impact of the APOA5 gene on insulin sensitivity and beta-cell function has not been examined. We examined the influence of 2 amino acid polymorphisms (V150M and G182C) in the APOA5 gene on insulin sensitivity and beta-cell function in 67 glucose-tolerant white subjects. Insulin sensitivity index (ISI) and first- and second-phase insulin responses (1stIR and 2ndIR) were assessed using a hyperglycemic clamp technique. We identified 59 VV and 8 VM subjects, and none had either the GC or CC genotype. Although no association was found with fasting lipid profile and plasma glucose concentrations during oral glucose tolerance test, the V150M was associated with higher 1stIR (P = 0.0010) and 2ndIR (P = 0.0016) and lower ISI (P = 0.0135). The associations of this polymorphism with 1stIR (P = 0.0081) and 2ndIR (P = 0.0087) were independent of sex, age, and body mass index, but not ISI. The V150M polymorphism had an independent influence on 1stIR and 2ndIR. Although the biologic consequence of this polymorphism remains to be determined, the V150M polymorphism in the APOA5 gene is a genetic marker for beta-cell function. Show less