Laurence A. Rubin

Functional variants of OCTN cation transporter genes are associated with Crohn disease

Crohn disease is a chronic, inflammatory disease of the gastrointestinal tract. A locus of ∼250 kb at 5q31 (IBD5) was previously associated with susceptibility to Crohn disease, as indicated by increased prevalence of a risk haplotype of 11 single-nucleotide polymorphisms among individuals with Crohn disease, but the pathogenic lesion in the region has not yet been identified. We report here that two variants in the organic cation transporter cluster at 5q31 (a missense substitution in SLC22A4 and a G→C transversion in the SLC22A5 promoter) form a haplotype associated with susceptibility to Crohn disease. These variants alter transcription and transporter functions of the organic cation transporters and interact with variants in another gene associated with Crohn disease, CARD15, to increase risk of Crohn disease. These results suggest that SLC22A4, SLC22A5 and CARD15 act in a common pathogenic pathway to cause Crohn disease.

The soluble interleukin-2 receptor: biology, function, and clinical application.

PURPOSE To review the biologic origin, functional characteristics, and current and potential clinical applications of a novel marker of immune system activation, the soluble interleukin-2 receptor (sIL-2R). DATA IDENTIFICATION Studies reported since 1985 were identified by a computer search using MEDLINE as well as from bibliographies of published work. STUDY SELECTION Sixty-two reports on the clinical applications of the sIL-2R, largely from peer-reviewed journals, were identified. These reports address the utility and significance of sIL-2R measurements in various conditions. Basic scientific investigations delineating the biochemical and molecular features of the human interleukin-2 receptor complex and the sIL-2R protein were reviewed. DATA EXTRACTION The validity of sIL-2R quantitation as an index of in-vivo immune system activation and its usefulness as a measure of disease activity and outcome were examined. RESULTS OF DATA ANALYSIS The quantitation of sIL-2R, a novel laboratory measure of in-vivo immune system activation, correlates reliably with disease activity in autoimmune inflammatory disorders, transplantation rejection, and specific infectious disorders. Markedly elevated serum sIL-2R levels are a particularly prominent feature of certain hematologic malignancies, such as human T lymphotropic retrovirus type I-associated adult T-cell leukemia and hairy cell leukemia, reflecting tumor burden and response to therapy. The sIL-2R level at disease onset may also reliably predict long-term prognosis in non-Hodgkin lymphoma, and it appears to provide an additional serologic measure in the assessment of clinical progression in patients with human immunodeficiency virus infection and the acquired immunodeficiency syndrome. CONCLUSIONS Studies have suggested that sIL-2R levels offer a rapid, reliable, and noninvasive measure of disease activity, response to therapy, and, in some cases, prognosis in a broad spectrum of conditions associated with T- or B-cell immune activation.

Determinants of Peak Bone Mass: Clinical and Genetic Analyses in a Young Female Canadian Cohort

Peak bone mass has been shown to be a significant predictor of risk for osteoporosis. Previous studies have demonstrated that skeletal mass accumulation is under strong genetic control, and efforts have been made to identify candidate loci. Determinants of peak bone mass also include diet, physical activity, hormonal status, and other clinical factors. The overall contribution of these factors, genetic and nongenetic, and their interaction in determining peak bone density status have not been delineated. Six hundred and seventy‐seven healthy unrelated Caucasian women ages 18–35 years were assessed. A detailed, standardized interview was conducted to evaluate lifestyle factors, menstrual and reproductive history, medical conditions, medication use, and family history of osteoporosis. Bone mineral density (BMD) was measured at the lumbar spine (L2–L4) and the femoral neck (hip) using dual‐energy X‐ray absorptiometry. Genotyping of the vitamin D receptor (VDR) locus at three polymorphic sites (BsmI, ApaI, and TaqI) was performed. In bivariate analyses, BMD at the lumbar spine and hip was positively correlated with weight, height, body mass index (BMI), and level of physical activity, both now and during adolescence, but negatively correlated with a family history of osteoporosis. Hip, but not spine BMD, correlated positively with dietary intake of calcium, and negatively with amenorrhea of more than 3 months, with caffeine intake, and with age. Spine, but not hip BMD, correlated positively with age and with number of pregnancies. VDR haplotype demonstrated significant associations with BMD at the hip, level of physical activity currently, and BMI. In multivariate analysis, independent predictors of greater BMD (at the hip or spine) were: age (younger for the hip, older for the spine), greater body weight, greater height (hip only), higher level of physical activity now and during adolescence, no family history of osteoporosis, and VDR genotype (hip only). Weight, age, level of physical activity, and family history are independent predictors of peak BMD. Of these factors, weight accounts for over half the explained variability in BMD. VDR alleles are significant independent predictors of peak femoral neck, but not lumbar spine BMD, even after adjusting for family history of osteoporosis, weight, age, and exercise. However, the overall contribution of this genetic determinant is modest. Taken together, these factors explained ∼17% and 21% of the variability in peak spine and hip BMD, respectively, in our cohort. Future research should be aimed at further evaluation of genetic determinants of BMD. Most importantly, understanding the critical interactive nature between genes and the environment will facilitate development of targeted strategies directed at modifying lifestyle factors as well as earlier intervention in the most susceptible individuals.

A986S polymorphism of the calcium-sensing receptor and circulating calcium concentrations

BACKGROUND The regulation of extracellular calcium concentration by parathyroid hormone is mediated by a calcium-sensing, G-protein-coupled cell-surface receptor (CASR). Mutations of the CASR gene alter the set-point for extracellular ionised calcium [Ca2+]o and cause familial hypercalcaemia or hypocalcaemia. The CASR missense polymorphism, A986S, is common in the general population and is, therefore, a prime candidate as a genetic determinant of extracellular calcium concentration. METHODS We genotyped the CASR A986S variant (S allele frequency of 16.3%) in 163 healthy adult women and tested samples of their serum for total calcium, albumin, total protein, creatinine, phosphate, pH, and parathyroid hormone. A prospectively generated, random subset of 84 of these women provided a whole blood sample for assay of [Ca2+]o. FINDINGS The A986S genotype showed no association with total serum concentration of calcium, until corrected for albumin. In a multivariate regression model, biochemical and genetic variables accounted for 74% of the total variation in calcium. The significant predictors of serum calcium were: albumin (p<0.001), phosphate (p=0.02), parathyroid hormone (p=0.007), pH (p=0.001), and A986S genotype (p=0.009). Fasting whole-blood [Ca2+]o also showed an independent positive association with the 986S variant (p=0.013). INTERPRETATION The CASR A986S variant has a significant effect on extracellular calcium. The CASR A986S polymorphism is a likely candidate locus for genetic predisposition to various bone and mineral disorders in which extracellular calcium concentrations have a prominent part.

Vitamin D-receptor genotypes as independent genetic predictors of decreased bone mineral density in primary biliary cirrhosis.

BACKGROUND & AIMS Hepatic osteodystrophy is a complication of primary biliary cirrhosis (PBC). Allelic polymorphisms of the vitamin D receptor (VDR) gene are related to bone mineral density (BMD) in normal cohorts and those with primary osteoporosis. We sought to establish the prevalence of reduced bone mass in PBC, correlate BMD with VDR gene polymorphisms, and identify risk factors for the development of hepatic osteodystrophy. METHODS Seventy-two female patients with PBC were evaluated prospectively. Clinical information, BMD assessment, disease severity, and osteoporosis risk factors were documented, and multivariate regression modeling was performed. RESULTS Twenty-four percent of the patients were osteoporotic at the lumbar spine and 32% at the femur. Severe bone loss (z score <-2.0) occurs 4 times more frequently in patients with PBC compared with controls. Body weight (P = 0.003) and postmenopausal status (P = 0.012) correlated independently with BMD. VDR genotype (P = 0.01) correlated with lower BMD at the spine only. CONCLUSIONS Osteoporosis is a common complication of PBC. VDR genotype predicts lower BMD in patients with PBC. Studies are warranted to investigate the mechanism(s) by which VDR as well as other candidate genes may contribute to the development of hepatic osteodystrophy in PBC.

Bone Mineral Density Testing and Osteoporosis Education Improve Lifestyle Behaviors in Premenopausal Women: A Prospective Study

One way to decrease the risk of osteoporosis is to maximize peak bone mass. Peak bone mass may be moderately influenced by lifestyle behaviors: increasing calcium and exercise, decreasing alcohol intake and smoking may increase peak bone mass. We examined the effects of osteoporosis education and bone mineral density (BMD) testing on self‐reported lifestyle behaviors in 669 premenopausal women enrolled in a prospective study to assess determinants of peak bone mass. Study participants completed a questionnaire that assessed lifestyle behaviors, received pamphlets about osteoporosis, and had BMD testing. One year later, the women completed a similar questionnaire. After education about osteoporosis and BMD testing, women reported that they were less likely to smoke (odds ratio [OR] = 0.55; 95% confidence interval [95% CI]: 0.28–1.0), consume alcohol (OR = 0.13; 95% CI: 0.04–0.34), and caffeinated beverages (OR = 0.43; 95% CI: 0.27–0.68). Women were more likely to use calcium supplements (OR = 4.3; 95% CI: 3.04–6.2), vitamin D supplements (OR = 12.6; 95% CI: 7.4–22.9), and drink at least one glass of milk a day (OR = 13.3; 95% CI: 7.8–23.9). Further, women with low bone mass were more likely to use calcium supplements (OR = 1.7; 95% CI: 1.2–2.3) and vitamin D supplements (OR = 1.6; 95% CI: 1.1–2.2) compared with women who had normal bone mass. Thus, our intervention improved self‐reported lifestyle behaviors in premenopausal women. Such behaviors may ultimately increase peak bone mass and decrease the risk of developing osteoporosis.

The molecular basis for the generation of the human soluble interleukin 2 receptor

Using an enzyme-linked immunosorbent assay (ELISA) employing two monoclonal antibodies recognizing distinct epitopes on the interleukin 2 receptor (IL2R) alpha chain (Tac molecule), we previously demonstrated that activated lymphocytes release a soluble interleukin 2 receptor molecule (sIL2R) in vitro and in vivo. The sIL2R is biochemically and structurally related to Tac, but its precise origin and functional role remain to be defined. We report here that a single IL2R cDNA is sufficient to direct the synthesis of both cell-associated and soluble released IL2R molecules. Northern analysis of IL2R cDNA transfected L-cell lines revealed the presence of mRNA species unaccounted for by known transcription termination or internal splice sites. Nevertheless, S1 nuclease digestion studies failed to detect alternately spliced mRNA transcripts that specifically lack transmembrane or cytoplasmic domains and which may encode a secreted IL2R molecule. Therefore sIL2R does not appear to be the product of a unique post-transcriptional splicing event. In the absence of any post-translational modifications, sIL2R is most likely generated by enzymatic cleavage and release of cell surface Tac. This proteolytic release of Tac may be but one example of a common cellular mechanism for regulating the membrane expression of cell surface molecules.

Elevated Serum Levels of Soluble Tac Peptide in Adult T-Cell Leukemia: Correlation with Clinical Status during Chemotherapy

Adult T-cell leukemia associated with human T-cell leukemia virus type I (HTLV-I) is characterized by a clonal expansion of a CD4-positive subset of T lymphocytes that constitutively express high numbers of interleukin-2 receptors and that frequently infiltrate the skin; osteolytic bone lesions, and hypercalcemia. Using an enzyme-linked immunosorbent assay (ELISA) test, we measured the level of soluble Tac peptide, one chain of the human interleukin-2 receptor, in the serum of 50 patients with adult T-cell leukemia (38 Japanese and 12 American patients), 8 patients with other hematologic malignancies, 8 asymptomatic HTLV-I-antibody-positive carriers, and 17 normal controls. The serum level of soluble Tac peptide (geometric mean U/mL, 95% CI) was elevated at presentation in all patients with adult T-cell leukemia (16,461; 819 to 330,896) when compared with normal controls (238; 112 to 502), patients with other hematologic malignancies (1302; 475 to 3569), and healthy HTLV-I antibody-positive carriers (490; 115 to 2086). The highest levels were seen in patients (n = 33) with acute (32,154; 2587 to 399,598) compared with chronic (5464; 661 to 45,156) disease (n = 14). Serum levels of Tac peptide also tended to be more elevated in patients with adult T-cell leukemia with hypercalcemia (32,072; 2461 to 417,908) compared with normocalcemic patients (13,885; 496 to 388,436). Serial measurements of soluble Tac peptide levels in serum were done in four patients with adult T-cell leukemia during chemotherapy and the levels reflected disease activity. These observations suggest that the measurement of soluble Tac peptide levels in patients with adult T-cell leukemia is useful as a noninvasive measure of tumor burden and will help in the diagnosis of the disease and management of these patients.

Is there a relationship between autoantibodies and silicone-gel implants?

The present study was conducted to determine if 200 patients with silicone-gel implants demonstrated elevated levels of autoantibodies, compared with a similar group of 100 age-matched control subjects without breast implants. These results were then compared with 29 patients who had demonstrated implant rupture. Differences in the frequency of autoantibody levels were determined by the chi-squared test. Differences in autoantibody titers were determined by Wilcoxons signed rank test. Differences were considered significant with p > 0.05. The prevalence of a positive antinuclear antibody (ANA) test (dilution 1:100) in the 200 patients with breast implants was 26.5% compared with 28% in the 100 control subjects. In 29 patients with implant rupture, only 17.2% tested ANA positive. These values were not significantly different. In addition, there were no significant differences between the ANA titers of positive patients in each group. In each of the three groups, all patients who tested ANA positive were analyzed to assess the frequency and titer of other autoantibodies, including anti-DNA, anti‐cardiolipin, anti-SSA, anti-SSB, anti-SM, anti-RNP, and anti-Scl-70. There were no significant differences between the frequency or titer of any of these autoantibody levels in each of the three groups of patients. These studies strengthen the concept that there is no conclusive evidence that silicone-gel implants are related to the development of connective tissue disease.

Alleles of the Estrogen Receptor α‐Gene and an Estrogen Receptor Cotranscriptional Activator Gene, Amplified in Breast Cancer‐1 (AIB1), Are Associated with Quantitative Calcaneal Ultrasound

Quantitative bone ultrasound (QUS) has a significant heritable component. Because estrogen is required for attainment of peak bone mass, we studied alleles of two genes, estrogen receptor α (ER1) and amplified in breast cancer‐1 (AIB1), for their association with QUS. In a volunteer sample of 663 white women aged 18–35 years, bone ultrasound attenuation (BUA), speed of sound (SOS), and heel stiffness index (SI), the latter consisting of the component measures of BUA and SOS, were measured at the right calcaneus by QUS. Subjects were genotyped for the ER1 polymorphisms Xba I and Pvu II and for the AIB1 polyglutamine tract polymorphism. In a multiple regression analysis, ER1 genotype was an independent predictor of QUS‐SI (p = 0.03). Because AIB1 and ER1 enhance gene expression in a coordinate manner, we also searched for interactions. A gene‐by‐gene interaction effect was seen for QUS‐SI (p = 0.009), QUS‐BUA (p = 0.03), and QUS‐SOS (p = 0.004). These remained significant after the inclusion of clinically relevant variables into the final regression model. Overall, these clinical and genetic factors accounted for up to 16% of the variance in peak QUS; the genetic markers alone accounted for 4–7%. This is the first demonstration of specific genetic effects on calcaneal QUS encoded by alleles of genes directly involved in mediating estrogen effects on bone.