2021 Allan Award

This article is based on the address given by the author at the meeting of the American Society of Human Genetics (ASHG) held virtually October 18-22, 2021. The video of the original address can be found at the ASHG website.

An unsupervised learning approach to identify novel signatures of health and disease from multimodal data

BACKGROUND

Modern medicine is rapidly moving towards a data-driven paradigm based on comprehensive multimodal health assessments. Integrated analysis of data from different modalities has the potential of uncovering novel biomarkers and disease signatures.

METHODS

We collected 1385 data features from diverse modalities, including metabolome, microbiome, genetics, and advanced imaging, from 1253 individuals and from a longitudinal validation cohort of 1083 individuals. We utilized a combination of unsupervised machine learning methods to identify multimodal biomarker signatures of health and disease risk.

RESULTS

Our method identified a set of cardiometabolic biomarkers that goes beyond standard clinical biomarkers. Stratification of individuals based on the signatures of these biomarkers identified distinct subsets of individuals with similar health statuses. Subset membership was a better predictor for diabetes than established clinical biomarkers such as glucose, insulin resistance, and body mass index. The novel biomarkers in the diabetes signature included 1-stearoyl-2-dihomo-linolenoyl-GPC and 1-(1-enyl-palmitoyl)-2-oleoyl-GPC. Another metabolite, cinnamoylglycine, was identified as a potential biomarker for both gut microbiome health and lean mass percentage. We identified potential early signatures for hypertension and a poor metabolic health outcome. Additionally, we found novel associations between a uremic toxin, p-cresol sulfate, and the abundance of the microbiome genera Intestinimonas and an unclassified genus in the Erysipelotrichaceae family.

CONCLUSIONS

Our methodology and results demonstrate the potential of multimodal data integration, from the identification of novel biomarker signatures to a data-driven stratification of individuals into disease subtypes and stages-an essential step towards personalized, preventative health risk assessment.

Predispositional genome sequencing in healthy adults: design, participant characteristics, and early outcomes of the PeopleSeq Consortium

BACKGROUND

Increasing numbers of healthy individuals are undergoing predispositional personal genome sequencing. Here we describe the design and early outcomes of the PeopleSeq Consortium, a multi-cohort collaboration of predispositional genome sequencing projects, which is examining the medical, behavioral, and economic outcomes of returning genomic sequencing information to healthy individuals.

METHODS

Apparently healthy adults who participated in four of the sequencing projects in the Consortium were included. Web-based surveys were administered before and after genomic results disclosure, or in some cases only after results disclosure. Surveys inquired about sociodemographic characteristics, motivations and concerns, behavioral and medical responses to sequencing results, and perceived utility.

RESULTS

Among 1395 eligible individuals, 658 enrolled in the Consortium when contacted and 543 have completed a survey after receiving their genomic results thus far (mean age 53.0 years, 61.4% male, 91.7% white, 95.5% college graduates). Most participants (98.1%) were motivated to undergo sequencing because of curiosity about their genetic make-up. The most commonly reported concerns prior to pursuing sequencing included how well the results would predict future risk (59.2%) and the complexity of genetic variant interpretation (56.8%), while 47.8% of participants were concerned about the privacy of their genetic information. Half of participants reported discussing their genomic results with a healthcare provider during a median of 8.0 months after receiving the results; 13.5% reported making an additional appointment with a healthcare provider specifically because of their results. Few participants (< 10%) reported making changes to their diet, exercise habits, or insurance coverage because of their results. Many participants (39.5%) reported learning something new to improve their health that they did not know before. Reporting regret or harm from the decision to undergo sequencing was rare (< 3.0%).

CONCLUSIONS

Healthy individuals who underwent predispositional sequencing expressed some concern around privacy prior to pursuing sequencing, but were enthusiastic about their experience and not distressed by their results. While reporting value in their health-related results, few participants reported making medical or lifestyle changes.

Profound Perturbation of the Metabolome in Obesity Is Associated with Health Risk

Obesity is a heterogeneous phenotype that is crudely measured by body mass index (BMI). There is a need for a more precise yet portable method of phenotyping and categorizing risk in large numbers of people with obesity to advance clinical care and drug development. Here, we used non-targeted metabolomics and whole-genome sequencing to identify metabolic and genetic signatures of obesity. We find that obesity results in profound perturbation of the metabolome; nearly a third of the assayed metabolites associated with changes in BMI. A metabolome signature identifies the healthy obese and lean individuals with abnormal metabolomes-these groups differ in health outcomes and underlying genetic risk. Specifically, an abnormal metabolome associated with a 2- to 5-fold increase in cardiovascular events when comparing individuals who were matched for BMI but had opposing metabolome signatures. Because metabolome profiling identifies clinically meaningful heterogeneity in obesity, this approach could help select patients for clinical trials.

Identification of Misclassified ClinVar Variants via Disease Population Prevalence

There is a significant interest in the standardized classification of human genetic variants. We used whole-genome sequence data from 10,495 unrelated individuals to contrast population frequency of pathogenic variants to the expected population prevalence of the disease. Analyses included the ACMG-recommended 59 gene-condition sets for incidental findings and 463 genes associated with 265 OrphaNet conditions. A total of 25,505 variants were used to identify patterns of inflation (i.e., excess genetic risk and misclassification). Inflation increases as the level of evidence supporting the pathogenic nature of the variant decreases. We observed up to 11.5% of genetic disorders with inflation in pathogenic variant sets and up to 92.3% for the variant set with conflicting interpretations. This improved to 7.7% and 57.7%, respectively, after filtering for disease-specific allele frequency. The patterns of inflation were replicated using public data from more than 138,000 genomes. The burden of rare variants was a main contributing factor of the observed inflation, indicating collective misclassified rare variants. We also analyzed the dynamics of re-classification of variant pathogenicity in ClinVar over time, which indicates progressive improvement in variant classification. The study shows that databases include a significant proportion of wrongly ascertained variants; however, it underscores the critical role of ClinVar to contrast claims and foster validation across submitters.

Aberrant GlyRS-HDAC6 interaction linked to axonal transport deficits in Charcot-Marie-Tooth neuropathy

Dominant mutations in glycyl-tRNA synthetase (GlyRS) cause a subtype of Charcot-Marie-Tooth neuropathy (CMT2D). Although previous studies have shown that GlyRS mutants aberrantly interact with Nrp1, giving insight into the disease’s specific effects on motor neurons, these cannot explain length-dependent axonal degeneration. Here, we report that GlyRS mutants interact aberrantly with HDAC6 and stimulate its deacetylase activity on α-tubulin. A decrease in α-tubulin acetylation and deficits in axonal transport are observed in mice peripheral nerves prior to disease onset. An HDAC6 inhibitor used to restore α-tubulin acetylation rescues axonal transport deficits and improves motor functions of CMT2D mice. These results link the aberrant GlyRS-HDAC6 interaction to CMT2D pathology and suggest HDAC6 as an effective therapeutic target. Moreover, the HDAC6 interaction differs from Nrp1 interaction among GlyRS mutants and correlates with divergent clinical presentations, indicating the existence of multiple and different mechanisms in CMT2D.

Mutations in glycyl-tRNA synthetase (GlyRS) cause Charcot-Marie-Tooth disease, a neuromuscular disorder characterized by axonal degeneration. Here the authors show that mutant GlyRS interacts with histone deacetylase 6, resulting in increased deacetylation of α-tubulin and axonal transport deficits.

Profiling of Short-Tandem-Repeat Disease Alleles in 12,632 Human Whole Genomes

Short tandem repeats (STRs) are hyper-mutable sequences in the human genome. They are often used in forensics and population genetics and are also the underlying cause of many genetic diseases. There are challenges associated with accurately determining the length polymorphism of STR loci in the genome by next-generation sequencing (NGS). In particular, accurate detection of pathological STR expansion is limited by the sequence read length during whole-genome analysis. We developed TREDPARSE, a software package that incorporates various cues from read alignment and paired-end distance distribution, as well as a sequence stutter model, in a probabilistic framework to infer repeat sizes for genetic loci, and we used this software to infer repeat sizes for 30 known disease loci. Using simulated data, we show that TREDPARSE outperforms other available software. We sampled the full genome sequences of 12,632 individuals to an average read depth of approximately 30× to 40× with Illumina HiSeq X. We identified 138 individuals with risk alleles at 15 STR disease loci. We validated a representative subset of the samples (n = 19) by Sanger and by Oxford Nanopore sequencing. Additionally, we validated the STR calls against known allele sizes in a set of GeT-RM reference cell-line materials (n = 6). Several STR loci that are entirely guanine or cytosines (G or C) have insufficient read evidence for inference and therefore could not be assayed precisely by TREDPARSE. TREDPARSE extends the limit of STR size detection beyond the physical sequence read length. This extension is critical because many of the disease risk cutoffs are close to or beyond the short sequence read length of 100 to 150 bases.

An international effort towards developing standards for best practices in analysis, interpretation and reporting of clinical genome sequencing results in the CLARITY Challenge

Background

There is tremendous potential for genome sequencing to improve clinical diagnosis and care once it becomes routinely accessible, but this will require formalizing research methods into clinical best practices in the areas of sequence data generation, analysis, interpretation and reporting. The CLARITY Challenge was designed to spur convergence in methods for diagnosing genetic disease starting from clinical case history and genome sequencing data. DNA samples were obtained from three families with heritable genetic disorders and genomic sequence data were donated by sequencing platform vendors. The challenge was to analyze and interpret these data with the goals of identifying disease-causing variants and reporting the findings in a clinically useful format. Participating contestant groups were solicited broadly, and an independent panel of judges evaluated their performance.

Results

A total of 30 international groups were engaged. The entries reveal a general convergence of practices on most elements of the analysis and interpretation process. However, even given this commonality of approach, only two groups identified the consensus candidate variants in all disease cases, demonstrating a need for consistent fine-tuning of the generally accepted methods. There was greater diversity of the final clinical report content and in the patient consenting process, demonstrating that these areas require additional exploration and standardization.

Conclusions

The CLARITY Challenge provides a comprehensive assessment of current practices for using genome sequencing to diagnose and report genetic diseases. There is remarkable convergence in bioinformatic techniques, but medical interpretation and reporting are areas that require further development by many groups.

Adult genetic risk screening

Recent advances in genetic analysis especially DNA sequencing technology open a new strategy for adult disease prevention by genetic screening. Physicians presently treat disease pathology with less emphasis on disease risk prevention/reduction. Genetic screening has reduced the incidence of untreatable childhood genetic diseases and improved the care of newborns. The opportunity exists to expand screening programs and reduce the incidence of adult onset diseases via genetic risk identification and disease intervention. This article outlines the approach, challenges, and benefits of such screening for adult genetic disease risks.

Truncating mutations of MAGEL2 cause Prader-Willi phenotypes and autism

Prader-Willi syndrome (PWS) is caused by the absence of paternally expressed, maternally silenced genes at 15q11-q13. We report four individuals with truncating mutations on the paternal allele of MAGEL2, a gene within the PWS domain. The first subject was ascertained by whole-genome sequencing analysis for PWS features. Three additional subjects were identified by reviewing the results of exome sequencing of 1,248 cases in a clinical laboratory. All four subjects had autism spectrum disorder (ASD), intellectual disability and a varying degree of clinical and behavioral features of PWS. These findings suggest that MAGEL2 is a new gene causing complex ASD and that MAGEL2 loss of function can contribute to several aspects of the PWS phenotype.

P5-12-04: Genetic Linkage between Acquired and Primary Lymphedema Evaluated through Whole Exome Sequencing and NIR Fluorescence Lymphatic Imaging

Acquired lymphedema is thought to arise from the damage of the lymphatic vasculature that transports excess fluid and macromolecules away from tissues for return to the blood vasculature. The onset of the cancer acquired disease can occur months to years after lymph node dissection and manifests itself as an accumulation of fluid and macromolecules in tissues that leads to edema and irresolvable swelling. The rare disease of primary lymphedema is identical to cancer acquired lymphedema, with the exception that there is no trauma or cancer treatment that can be attributed as its cause. Primary lymphedema has been attributed to genetic causes since the late nineteenth century. Although there are five known genetic causes of hereditary or primary lymphedema, the majority of patients with lymphedema do not possess mutations in these genes. More recently, it has been proposed that a genetic link between cancer acquired and primary lymphedema exists. If a genetic susceptibility for cancer acquired lymphedema could be found, then we could predict which survivors will encounter the disease and could develop new therapies which are more effective than the current treatments that have remained unchanged for the past 80 years.

In an FDA approved investigational study, we used near-infrared (NIR) fluorescence imaging to phenotype the lymphatic architecture of subjects with both acquired and primary lymphedema, as well as their unaffected family members. We collected blood for DNA analyses. NIR fluorescence provided the phenotype of abnormal lymphatic function while whole exome sequencing provided the genotype. Bioinformatics analyses were then used to identify causative genes using cosegregation of familial genotypes using the phentotypes found through NIR fluorescence imaging.

The first family analyzed had members with primary and acquired lymphedema in which mutations encoding for proteins that participate in the HGF/c-MET and PI3K pathways could potentially explain the inheritance of lymphedema in this family. The father and affected daughters were heterozygous for a de novo SNP HGF in the kringle binding domain that interacts with tyrosine kinase receptor c-MET. The father had a normal lymphatic phenotype. On the other hand, the mother and daughters were heterozygous for the de novo mutation of INPPL1 (SHIP-2), adjacent to the SH2 domain of the protein that is known to bind to the multifunctional docking site of c-MET and associates with proteins in the Rho pathway for cytoskeletal reorganization. The daughters possessed both HGF and INPPL1 mutations and were diagnosed with primary lymphedema while the mother, who possessed the INPPL1 mutation, was diagnosed at the time of NIR imaging with acquired lymphedema. Analyses of remaining families as well as breast cancer related lymphedema patients are underway to confirm whether INPPL1 may be a candidate susceptibility gene for acquired lymphedema. Supported in parts by R01 HL092923 and CA128919, The Texas Star Award, and the Cullen Foundation.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-12-04.

Deficiencies of glucosamine-6-sulfate or galactosamine-6-sulfate sulfatases are responsible for different mucopolysaccharidoses

[1-3H]Galactitol-6-sulfate, N- [1-3H]acetylgalactosaminitol-6-sulfate, N-[1-3H]acetylglucosaminitol-6-sulfate, N-acetylglucosamine-6-sulfate, and 6-sulfated tetrasaccharides from chondroitin-6-sulfate have been used for the measurement of 6-sulfatase activity of extracts of normal skin fibroblasts and of fibroblasts cultured from patients with genetic mucopolysaccharidoses. With these substrates, extracts of fibroblasts derived from Morquio patients lack or have greatly reduced activities for galactitol-6-sulfate, N-acetylgalactosaminitol-6-sulfate, and 6-sulfated tetrasaccharides but have normal activity for N-acetylglucosamine-6-sulfate and its alditol; those derived from a patient with a newly discovered mucopolysaccharidosis have greatly reduced activity for N-acetylglucosamine-6-sulfate and its alditol but normal activity for galactitol-6-sulfate, N-acetylgalactosaminitol-6-sulfate, and the 6-sulfated tetrasaccharides. These findings demonstrate the existence of two different hexosamine-6-sulfate sulfatases, specific for the glucose or galactose configuration of their substrates. Their respective deficiencies, causing inability to degrade keratan sulfate and heparan sulfate in one case and keratan sulfate and chondroitin-6-sulfate in the other, are responsible for different clinical phenotypes.

The drug development crisis: efficiency and safety

Despite advancements in genetics, chemistry, and protein engineering, recent years have seen fewer approvals of new drugs, increases in development costs, and high-profile drug withdrawals. This article focuses on technologic methods for improving drug development efficiency. These technologies include high-content cell screening, expression profiling, mass spectroscopy, mouse models of disease, and a post-launch screening program that enables investigations of adverse drug effects. Implementation of these new technologies promises to improve performance in drug development and safety.

Correction of chromosomal mutation and random integration in embryonic stem cells with helper-dependent adenoviral vectors

For gene therapy of inherited diseases, targeted integration/gene repair through homologous recombination (HR) between exogenous and chromosomal DNA would be an ideal strategy to avoid potentially serious problems of random integration such as cellular transformation and gene silencing. Efficient sequence-specific modification of chromosomes by HR would also advance both biological studies and therapeutic applications of a variety of stem cells. Toward these goals, we developed an improved strategy of adenoviral vector (AdV)-mediated HR and examined its ability to correct an insertional mutation in the hypoxanthine phosphoribosyl transferase (Hprt) locus in male mouse ES cells. The efficiency of HR was compared between four types of AdVs that contained various lengths of homologies at the Hprt locus and with various multiplicities of infections. The frequency of HR with helper-dependent AdVs (HD AdVs) with an 18.6-kb homology reached 0.2% per transduced cell at a multiplicity of infection of 10 genomes per cell. Detection of random integration at DNA levels by PCR revealed extremely high efficiency of 5% per cell. We also isolated and characterized chromosomal sites where HD AdVs integrated in a random manner. In contrast to retroviral, lentiviral, and adeno-associated viral vectors, which tend to integrate into genes, the integration sites of AdV was distributed randomly inside and outside genes. These findings suggest that HR mediated by HD AdVs is efficient and relatively safe and might be a new viable option for ex vivo gene therapy as well as a tool for chromosomal manipulation of a variety of stem cells.

Monitoring expression of genes involved in drug metabolism and toxicology using DNA microarrays

Oligonucleotide DNA microarrays were investigated for utility in measuring global expression profiles of drug metabolism genes. This study was performed to investigate the feasibility of using microarray technology to minimize the long, expensive process of testing drug candidates for safety in animals. In an evaluation of hybridization specificity, microarray technology from Affymetrix distinguished genes up to a threshold of approximately 90% DNA identity. Oligonucleotides representing human cytochrome P-450 gene CYP3A5 showed heterologous hybridization to CYP3A4 and CYP3A7 RNAs. These genes could be clearly distinguished by selecting a subset of oligonucleotides that hybridized selectively to CYP3A5. Further validation of the technology was performed by measuring gene expression profiles in livers of rats treated with vehicle, 3-methylcholanthrene (3MC), phenobarbital, dexamethasone, or clofibrate and by confirming data for six genes using quantitative RT-PCR. Responses of drug metabolism genes, including CYPs, epoxide hydrolases (EHs), UDP-glucuronosyl transferases (UGTs), glutathione sulfotransferases (GSTs), sulfotransferases (STs), drug transporter genes, and peroxisomal genes, to these well-studied compounds agreed well with, and extended, published observations. Additional gene regulatory responses were noted that characterize metabolic effects or stress responses to these compounds. Thus microarray technology can provide a facile overview of gene expression responses relevant to drug metabolism and toxicology.

Identification of receptors for neuromedin U and its role in feeding

Neuromedin U (NMU) is a neuropeptide with potent activity on smooth muscle which was isolated first from porcine spinal cord and later from other species. It is widely distributed in the gut and central nervous system. Peripheral activities of NMU include stimulation of smooth muscle, increase of blood pressure, alteration of ion transport in the gut, control of local blood flow and regulation of adrenocortical function. An NMU receptor has not been molecularly identified. Here we show that the previously described orphan G-protein-coupled receptor FM-3 (ref. 15) and a newly discovered one (FM-4) are cognate receptors for NMU. FM-3, designated NMU1R, is abundantly expressed in peripheral tissues whereas FM-4, designated NMU2R, is expressed in specific regions of the brain. NMU is expressed in the ventromedial hypothalamus in the rat brain, and its level is significantly reduced following fasting. Intracerebroventricular administration of NMU markedly suppresses food intake in rats. These findings provide a molecular basis for the biochemical activities of NMU and may indicate that NMU is involved in the central control of feeding.

Optimization of the helper-dependent adenovirus system for production and potency in vivo

Helper-dependent (HD) adenoviral vectors devoid of all viral coding sequences provide for safe and highly efficient gene transfer with long-lasting transgene expression. High titer stocks of HD vectors can be generated by using the cre-recombinase system. However, we have encountered difficulties with this system, including rearranged HD vectors and variable efficiency of HD vector rescue. These problems represent a major hindrance, particularly with regard to large-scale production. To overcome these limitations, we have modified the system in two ways: We constructed a new helper virus with a modified packaging signal and enhanced growth characteristics. We also redesigned the vector backbones by including noncoding adenovirus sequences adjacent to the right inverted terminal repeat and by incorporated a number of different segments of noncoding DNA of human origin as "stuffer." Comparison of these vectors showed that the nature of the stuffer sequence affects replication of the HD vector. Optimization of the system resulted in a more robust and consistent production of HD vectors with low helper contamination and high in vivo potency.

Overexpression of M68/DcR3 in human gastrointestinal tract tumors independent of gene amplification and its location in a four-gene cluster

Fas-mediated apoptosis is an important regulator of cell survival, and abnormalities in this system have been shown to result in a number of human pathological conditions. A secreted member of the tumor necrosis factor receptor superfamily, DcR3, was recently reported to be amplified in human lung and colon cancers as a negative regulator of Fas-mediated apoptosis. We identified this gene, which we call M68. M68 genomic DNA, mRNA, and protein levels were examined in a series of human gastrointestinal tract tumors. Using M68 immunohistochemistry and a scoring system similar to that used for HER-2/neu, we found that M68 protein was overexpressed in 30 of 68 (44%) human adenocarcinomas of the esophagus, stomach, colon, and rectum. Tumors examined by Northern blot revealed M68 mRNA highly elevated in a similar fraction of primary tumors from the same gastrointestinal tract regions, as well as in the colon adenocarcinoma cell lines SW480 and SW1116. Further, we found M68 protein to be overexpressed in a substantial number of tumors in which gene amplification could not be detected by fluorescence in situ hybridization or quantitative genomic PCR, suggesting that overexpression of M68 may precede amplification in tumors. Finally, we find that M68 lies within a four-gene cluster that includes a novel helicase-like gene (NHL) related to RAD3/ERCC2, a plasma membrane Ras-related GTPase and a member of the stathmin family, amplification or overexpression of which may also contribute to cell growth and tumor progression.

Retina-specific nuclear receptor: A potential regulator of cellular retinaldehyde-binding protein expressed in retinal pigment epithelium and Müller glial cells

In an effort to identify nuclear receptors important in retinal disease, we screened a retina cDNA library for nuclear receptors. Here we describe the identification of a retina-specific nuclear receptor (RNR) from both human and mouse. Human RNR is a splice variant of the recently published photoreceptor cell-specific nuclear receptor [Kobayashi, M., Takezawa, S., Hara, K., Yu, R. T., Umesono, Y., Agata, K., Taniwaki, M., Yasuda, K. & Umesono, K. (1999) Proc. Natl. Acad. Sci. USA 96, 4814-4819] whereas the mouse RNR is a mouse ortholog. Northern blot and reverse transcription-PCR analyses of human mRNA samples demonstrate that RNR is expressed exclusively in the retina, with transcripts of approximately 7.5 kb, approximately 3.0 kb, and approximately 2.3 kb by Northern blot analysis. In situ hybridization with multiple probes on both primate and mouse eye sections demonstrates that RNR is expressed in the retinal pigment epithelium and in Müller glial cells. By using the Gal4 chimeric receptor/reporter cotransfection system, the ligand binding domain of RNR was found to repress transcriptional activity in the absence of exogenous ligand. Gel mobility shift assays revealed that RNR can interact with the promoter of the cellular retinaldehyde binding protein gene in the presence of retinoic acid receptor (RAR) and/or retinoid X receptor (RXR). These data raise the possibility that RNR acts to regulate the visual cycle through its interaction with cellular retinaldehyde binding protein and therefore may be a target for retinal diseases such as retinitis pigmentosa and age-related macular degeneration.

Identification of urotensin II as the endogenous ligand for the orphan G-protein-coupled receptor GPR14

Urotensin II (UII) is a neuropeptide with potent cardiovascular effects. Its sequence is strongly conserved among different species and has structural similarity to somatostatin. No receptor for UII has been molecularly identified from any species so far. GPR14 was cloned as an orphan G protein-coupled receptor with similarity to members of the somatostatin/opioid receptor family. We have now demonstrated that GPR14 is a high affinity receptor for UII and designate it UII-R1a. HEK293 cells and COS-7 cells transfected with rat GPR14 showed strong, dose-dependent calcium mobilization in response to fish, frog, and human UII. Radioligand binding analysis showed high affinity binding of UII to membrane preparations isolated from HEK293 cells stably expressing rat GPR14. In situ hybridization analysis showed that GPR14 was expressed in motor neurons of the spinal cord, smooth muscle cells of the bladder, and muscle cells of the heart. The identification of the first receptor for UII will allow better understanding of the physiological and pharmacological roles of UII.

Triplet repeat disorders: discussion of molecular mechanisms

Comparison of the growing number of disorders known to be associated with triplet repeat expansions reveals both common features and a diversity of molecular pathways. Despite significant progress towards the characterization of proteins coded by the mutant genes, the complex nature of these disorders requires identification of all molecular components of the triplet repeat pathways. In this brief review we will discuss recent progress in determining the molecular mechanisms of disorders with unstable trinucleotide mutations.

Characterization of the human cysteinyl leukotriene CysLT1 receptor

The cysteinyl leukotrienes-leukotriene C4(LTC4), leukotriene D4(LTD4) and leukotriene E4(LTE4)-are important mediators of human bronchial asthma. Pharmacological studies have determined that cysteinyl leukotrienes activate at least two receptors, designated CysLT1 and CysLT2. The CysLT1-selective antagonists, such as montelukast (Singulair), zafirlukast (Accolate) and pranlukast (Onon), are important in the treatment of asthma. Previous biochemical characterization of CysLT1 antagonists and the CysLT1 receptor has been in membrane preparations from tissues enriched for this receptor. Here we report the molecular and pharmacological characterization of the cloned human CysLT1 receptor. We describe the functional activation (calcium mobilization) of this receptor by LTD4 and LTC4, and competition for radiolabelled LTD4 binding to this receptor by the cysteinyl leukotrienes and three structurally distinct classes of CysLT1-receptor antagonists. We detected CysLT1-receptor messenger RNA in spleen, peripheral blood leukocytes and lung. In normal human lung, expression of the CysLT1-receptor mRNA was confined to smooth muscle cells and tissue macrophages. Finally, we mapped the human CysLT1-receptor gene to the X chromosome.