Novel pathogenic variants and quantitative phenotypic analyses of Robinow syndrome: WNT signaling perturbation and phenotypic variability.

Robinow syndrome (RS) is a genetically heterogeneous disorder with six genes that converge on the WNT/planar cell polarity (PCP) signaling pathway implicated (DVL1, DVL3, FZD2, NXN, ROR2, and WNT5A). RS is characterized by skeletal dysplasia and distinctive facial and physical characteristics. To further explore the genetic heterogeneity, paralog contribution, and phenotypic variability of RS, we investigated a cohort of 22 individuals clinically diagnosed with RS from 18 unrelated families. Pathogenic or likely pathogenic variants in genes associated with RS or RS phenocopies were identified in all 22 individuals, including the first variant to be reported in DVL2. We retrospectively collected medical records of 16 individuals from this cohort and extracted clinical descriptions from 52 previously published cases. We performed Human Phenotype Ontology (HPO) based quantitative phenotypic analyses to dissect allele-specific phenotypic differences. Individuals with FZD2 variants clustered into two groups with demonstrable phenotypic differences between those with missense and truncating alleles. Probands with biallelic NXN variants clustered together with the majority of probands carrying DVL1, DVL2, and DVL3 variants, demonstrating no phenotypic distinction between the NXN-autosomal recessive and dominant forms of RS. While phenotypically similar diseases on the RS differential matched through HPO analysis, clustering using phenotype similarity score placed RS-associated phenotypes in a unique cluster containing WNT5A, FZD2, and ROR2 apart from non-RS-associated paralogs. Through human phenotype analyses of this RS cohort and OMIM clinical synopses of Mendelian disease, this study begins to tease apart specific biologic roles for non-canonical WNT-pathway proteins.

A case study of atypical Larsen syndrome with absent hallmark joint dislocations.

BACKGROUND: A family with skeletal and craniofacial anomalies is presented. Whole-exome sequencing (WES) analysis indicated a diagnosis of Larsen syndrome, although their clinical presentation does not include the hallmark joint dislocations typically observed in Larsen syndrome. METHODS: Patient consent for the sharing of de-identified clinical and genetic information, along with use of photographs for publication, was obtained. WES and variant segregation analysis by WES were performed by commercial laboratory, GeneDx (Gaithersburg, MD), on peripheral blood samples from the proband, her brother, and her parents using methods detailed on their website for test XomeDx Whole Exome Sequencing Trio (https://www.genedx.com/test-catalog/available-tests/xomedx-whole-exome-sequencing-trio/). WES uses next-generation sequencing (NGS) technology to assess for variants within the coding regions, or exons, of approximately 23,000 genes. For the FLNB gene (NM_001457.3), 100% of the coding region was covered at a minimum of 10x. GeneDx uses Sanger sequencing to confirm NGS variants. RESULTS: WES revealed a heterozygous pathogenic variant, p.Glu227Lys (c.679G>A), in the FLNB gene in three out of the four family members tested. This variant is associated with Larsen syndrome, a skeletal dysplasia condition with a wide range of phenotypic variability that usually includes congenital joint dislocations. CONCLUSION: This is a highly unusual presentation of Larsen syndrome in which the identifying hallmark trait is absent in the patients' phenotypes.

Genomic analysis of an infant with intractable diarrhea and dilated cardiomyopathy.

We describe a case of an infant presenting with intractable diarrhea who subsequently developed dilated cardiomyopathy, for whom a diagnosis was not initially achieved despite extensive clinical testing, including panel-based genetic testing. Research-based whole-genome sequences of the proband and both parents were analyzed by the SAVANNA pipeline, a variant prioritization strategy integrating features of variants, genes, and phenotypes, which was implemented using publicly available tools. Although the intestinal morphological abnormalities characteristic of congenital tufting enteropathy (CTE) were not observed in the initial clinical gastrointestinal tract biopsies of the proband, an intronic variant, EPCAM c.556-14A>G, previously identified as pathogenic for CTE, was found in the homozygous state. A newborn cousin of the proband also presenting with intractable diarrhea was found to carry the same homozygous EPCAM variant, and clinical testing revealed intestinal tufting and loss of EPCAM staining. This variant, however, was considered nonexplanatory for the proband's dilated cardiomyopathy, which could be a sequela of the child's condition and/or related to other genetic variants, which include de novo mutations in the genes NEDD4L and GSK3A and a maternally inherited SCN5A variant. This study illustrates three ways in which genomic sequencing can aid in the diagnosis of clinically challenging patients: differential diagnosis despite atypical clinical presentation, distinguishing the possibilities of a syndromic condition versus multiple conditions, and generating hypotheses for novel contributory genes.