Navigating MARRVEL, a Web-Based Tool that Integrates Human Genomics and Model Organism Genetics Information

Through whole-exome/genome sequencing, human geneticists identify rare variants that segregate with disease phenotypes. To assess if a specific variant is ...

Baylor College of Medicine

One major challenge encountered with interpreting human genetic variants is the limited understanding of the functional impact of genetic alterations on biological processes. Furthermore, there remains an unmet demand for an efficient survey of the wealth of information on human homologs in model organisms across numerous databases. To efficiently assess the large volume of publically available information, it is important to provide a concise summary of the most relevant information in a rapid user-friendly format. To this end, we created MARRVEL (model organism aggregated resources for rare variant exploration). MARRVEL is a publicly available website that integrates information from six human genetic databases and seven model organism databases. For any given variant or gene, MARRVEL displays information from OMIM, ExAC, ClinVar, Geno2MP, DGV, and DECIPHER. Importantly, it curates model organism-specific databases to concurrently display a concise summary regarding the human gene homologs in budding and fission yeast, worm, fly, fish, mouse, and rat on a single webpage. Experiment-based information on tissue expression, protein subcellular localization, biological process, and molecular function for the human gene and homologs in the seven model organisms are arranged into a concise output. Hence, rather than visiting multiple separate databases for variant and gene analysis, users can obtain important information by searching once through MARRVEL. Altogether, MARRVEL dramatically improves efficiency and accessibility to data collection and facilitates analysis of human genes and variants by cross-disciplinary integration of 18 million records available in public databases to facilitate clinical diagnosis and basic research.

MARRVEL: Integration of Human and Model Organism Genetic Resources to Facilitate Functional Annotation of the Human Genome.

F-box and leucine-rich repeat protein 4 (FBXL4) is a mitochondrial protein whose exact function is not yet known. However, cellular studies have suggested that it plays significant roles in mitochondrial bioenergetics, mitochondrial DNA (mtDNA) maintenance, and mitochondrial dynamics. Biallelic pathogenic variants in FBXL4 are associated with an encephalopathic mtDNA maintenance defect syndrome that is a multisystem disease characterized by lactic acidemia, developmental delay, and hypotonia. Other features are feeding difficulties, growth failure, microcephaly, hyperammonemia, seizures, hypertrophic cardiomyopathy, elevated liver transaminases, recurrent infections, variable distinctive facial features, white matter abnormalities and cerebral atrophy found in neuroimaging, combined deficiencies of multiple electron transport complexes, and mtDNA depletion. Since its initial description in 2013, 36 different pathogenic variants in FBXL4 were reported in 50 affected individuals. In this report, we present 37 additional affected individuals and 11 previously unreported pathogenic variants. We summarize the clinical features of all 87 individuals with FBXL4-related mtDNA maintenance defect, review FBXL4 structure and function, map the 47 pathogenic variants onto the gene structure to assess the variants distribution, and investigate the genotype-phenotype correlation. Finally, we provide future directions to understand the disease mechanism and identify treatment strategies.

Molecular and clinical spectra of FBXL4 deficiency.

Mitochondrial DNA (mtDNA) maintenance defects are a group of diseases caused by deficiency of proteins involved in mtDNA synthesis, mitochondrial nucleotide supply, or mitochondrial dynamics. One of the mtDNA maintenance proteins is MPV17, which is a mitochondrial inner membrane protein involved in importing deoxynucleotides into the mitochondria. In 2006, pathogenic variants in MPV17 were first reported to cause infantile-onset hepatocerebral mtDNA depletion syndrome and Navajo neurohepatopathy. To date, 75 individuals with MPV17-related mtDNA maintenance defect have been reported with 39 different MPV17 pathogenic variants. In this report, we present an additional 25 affected individuals with nine novel MPV17 pathogenic variants. We summarize the clinical features of all 100 affected individuals and review the total 48 MPV17 pathogenic variants. The vast majority of affected individuals presented with an early-onset encephalohepatopathic disease characterized by hepatic and neurological manifestations, failure to thrive, lactic acidemia, and mtDNA depletion detected mainly in liver tissue. Rarely, MPV17 deficiency can cause a late-onset neuromyopathic disease characterized by myopathy and peripheral neuropathy with no or minimal liver involvement. Approximately half of the MPV17 pathogenic variants are missense. A genotype with biallelic missense variants, in particular homozygous p.R50Q, p.P98L, and p.R41Q, can carry a relatively better prognosis.

MPV17-related mitochondrial DNA maintenance defect: New cases and review of clinical, biochemical, and molecular aspects.

Mitochondrial DNA maintenance (mtDNA) defects have a wide range of causes, each with a set of phenotypes that overlap with many other neurological or muscular diseases. Clinicians face the challenge of narrowing down a long list of differential diagnosis when encountered with non-specific neuromuscular symptoms. Biallelic pathogenic variants in the Thymidine Kinase 2 (TK2) gene cause a myopathic form of mitochondrial DNA maintenance defect. Since the first description in 2001, there have been 71 patients reported with 42 unique pathogenic variants. Here we are reporting 11 new cases with 5 novel pathogenic variants. We describe and analyze a total of 82 cases with 47 unique TK2 pathogenic variants in effort to formulate a comprehensive molecular and clinical spectrum of TK2-related mtDNA maintenance disorders.

Clinical and molecular spectrum of thymidine kinase 2-related mtDNA maintenance defect.

Extra-muscular manifestations of TK2 deficiency.

Retinal function relies on precisely organized neurons and synapses and a properly patterned vasculature to support them. Alterations in these features can result in vision loss. However, our understanding of retinal organization pathways remains incomplete because of a lack of methods to rapidly identify neuron and vasculature regulators in mammals. Here we developed a pipeline for the identification of neural and synaptic integrity genes by high-throughput retinal screening (INSiGHT) that analyzes candidate expression, vascular patterning, cellular organization, and synaptic arrangement. Using this system, we examined 102 mutant mouse lines and identified 16 unique retinal regulatory genes. Fifteen of these candidates are identified as novel retina regulators, and many (9 of 16) are associated with human neural diseases. These results expand the genetic landscape involved in retinal circuit organization and provide a road map for continued discovery of mammalian retinal regulators and disease-causing alleles.

Rapid and Integrative Discovery of Retina Regulatory Molecules.

An increasing number of mitochondrial diseases are found to be caused by pathogenic variants in nuclear encoded mitochondrial aminoacyl-tRNA synthetases. FARS2 encodes mitochondrial phenylalanyl-tRNA synthetase (mtPheRS) which transfers phenylalanine to its cognate tRNA in mitochondria. Since the first case was reported in 2012, a total of 21 subjects with FARS2 deficiency have been reported to date with a spectrum of disease severity that falls between two phenotypes; early onset epileptic encephalopathy and a less severe phenotype characterized by spastic paraplegia. In this report, we present an additional 15 individuals from 12 families who are mostly Arabs homozygous for the pathogenic variant Y144C, which is associated with the more severe early onset phenotype. The total number of unique pathogenic FARS2 variants known to date is 21 including three different partial gene deletions reported in four individuals. Except for the large deletions, all variants but two (one in-frame deletion of one amino acid and one splice-site variant) are missense. All large deletions and the single splice-site variant are in trans with a missense variant. This suggests that complete loss of function may be incompatible with life. In this report, we also review structural, functional, and evolutionary significance of select FARS2 pathogenic variants reported here.

FARS2 deficiency; new cases, review of clinical, biochemical, and molecular spectra, and variants interpretation based on structural, functional, and evolutionary significance.

Julia Wang

Program in Developmental Biology,
Medical Scientist Training Program

Baylor College of Medicine

Navigating MARRVEL, a Web-Based Tool that Integrates Human Genomics and Model Organism Genetics Information

Julia Wang

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Program in Developmental Biology,Medical Scientist Training Program

Baylor College of Medicine

Navigating MARRVEL, a Web-Based Tool that Integrates Human Genomics and Model Organism Genetics Information

Program in Developmental Biology,
Medical Scientist Training Program