A Heterozygous Missense Variant in MAP2K2 in a Stillborn Romagnola Calf with Skeletal-Cardio-Enteric Dysplasia

Simple Summary

Skeletal dysplasias encompass a clinical-, pathological- and genetically heterogeneous group of disorders characterized by abnormal cartilage and/or bone formation, growth, and remodeling. They may belong to the so-called RASopathies, congenital conditions caused by heterozygous variants in genes that encode components of the Ras/mitogen-activated protein kinase (MAPK) cell signaling pathway. Herein, an affected calf of the Italian Romagnola breed was reported showing a skeletal-cardio-enteric dysplasia. We identified a most likely disease-causing mutation in the MAP2K2 gene by whole-genome sequencing (WGS). The MAP2K2 gene is known to be related with dominant inherited cardio-facio-cutaneous syndrome in humans, but it was so far unknown to cause a similar disease in domestic animals. We assume that the identified missense variant that was predicted to impair the function of the protein, occurred either within the germline of the dam or post-zygotically in the embryo. Rare lethal diseases such as the skeletal-cardio-enteric dysplasia in livestock are usually not characterized to the molecular level, mainly because of the lack of funds and diagnostic opportunities. Precise WGS-based diagnostics enables the understanding of rare diseases and supports the value of monitoring cattle breeding populations for fatal genetic defects.

Abstract

RASopathies are a group of developmental disorders caused by dominant mutations in genes that encode components of the Ras/mitogen-activated protein kinase (MAPK) cell signaling pathway. The goal of this study was to characterize the pathological phenotype of a Romagnola stillborn calf with skeletal-cardio-enteric dysplasia and to identify a genetic cause by whole-genome sequencing (WGS). The calf showed reduced fetal growth, a short-spine, a long and narrow face, cardiac defects and heterotopy of the spiral colon. Genetic analysis revealed a private heterozygous missense variant in MAP2K2:p.Arg179Trp, located in the protein kinase domain in the calf, and not found in more than 4500 control genomes including its sire. The identified variant affecting a conserved residue was predicted to be deleterious and most likely occurred de novo. This represents the first example of a dominant acting, and most likely pathogenic, variant in MAP2K2 in domestic animals, thereby providing the first MAP2K2-related large animal model, especially in respect to the enteric malformation. In addition, this study demonstrates the utility of WGS-based precise diagnostics for understanding sporadic congenital syndromic anomalies in cattle and the general utility of continuous surveillance for rare hereditary defects in cattle.

Autosomal dominant brachyolmia in a large Swedish family: phenotypic spectrum and natural course

Autosomal dominant brachyolmia (Type 3, OMIM #113500) belongs to a group of skeletal dysplasias caused by mutations in the transient receptor potential cation channel, subfamily V, member 4 (TRPV4) gene, encoding a Ca++-permeable, non-selective cation channel. The disorder is characterized by disproportionate short stature with short trunk, scoliosis and platyspondyly. The phenotypic variability and long-term natural course remain inadequately characterized. The purpose of this study was to describe a large Swedish family with brachyolmia type 3 due to a heterozygous TRPV4 mutation c.1847G>A (p.R616Q) in 11 individuals. The mutation has previously been detected in another family with autosomal dominant brachyolmia [Rock et al., 2008]. Review of hospital records and patient assessments indicated that clinical symptoms of brachyolmia became evident by school age with chronic pain in the spine and hips; radiographic changes were evident earlier. Growth was not affected during early childhood but deteriorated with age in some patients due to increasing spinal involvement. Affected individuals had a wide range of subjective symptoms with chronic pain in the extremities and the spine, and paresthesias. Our findings indicate that autosomal dominant brachyolmia may be associated with significant long-term morbidity, as seen in this family.