Variants in CLCN1 and PDE4C Associated with Muscle Hypertrophy, Dysphagia, and Gait Abnormalities in Young French Bulldogs.

Simple Summary: Muscle hypertrophy, swallowing disorders, and gait abnormalities are clinical signs common to many muscle diseases, including muscular dystrophies, non-dystrophic myotonias, myopathies associated with deficiency of myostatin, and acquired inflammatory myopathies. Here we describe four clinical cases in young French bulldogs displaying the above clinical signs. Using whole genome sequencing in two of the cases and Sanger sequencing validation, variants were identified in the chloride channel gene CLCN1, which causes non-dystrophic congenital myotonia, and in the phosphodiesterase gene PDE4C, which is the major phosphodiesterase expressed in skeletal muscle and may play a role in decreasing muscle atrophy. In one case for which whole genome sequencing was not performed, genotyping for the identified variants was not confirmed. In the remaining case, the CLCN1 variant was confirmed with genotyping. Identification of variants in genes associated with this clinical presentation may assist breeders with breeding programs designed to eliminate them in this currently very popular breed. Further, identification of new disease-causing variants may help us to identify therapies to reverse muscle atrophy in individuals affected by this group of neuromuscular diseases. (1) Background: Muscle hypertrophy, swallowing disorders, and gait abnormalities are clinical signs common to many muscle diseases, including muscular dystrophies, non-dystrophic myotonias, genetic myopathies associated with deficiency of myostatin, and acquired inflammatory myopathies. Here, we investigated underlying causes of this triad of clinical signs in four young French bulldogs via muscle histopathology coupled with whole genome and Sanger sequencing. (2) Methods: Dogs were evaluated by veterinary clinical internists and neurologists, and biopsies were obtained for histopathological diagnosis. DNA was submitted for whole genome sequencing, followed by bioinformatics evaluation and confirmation of variants via Sanger sequencing in two cases. (3) Results: Two novel variants were identified. The first, found in two related French bulldogs, was a homozygous variant in the chloride channel gene CLCN1 known to cause non-dystrophic congenital myotonia, and the second, found in an unrelated French bulldog, was a heterozygous variant in the cAMP phosphodiesterase gene PDE4C, which is the major phosphodiesterase expressed in skeletal muscle and may play a role in decreasing muscle atrophy. An underlying molecular basis in one other case has not yet been identified. (4) Conclusions: Here, we identified two novel variants, one in the CLCN1 and one in the PDE4C gene, associated with clinical signs of muscle hypertrophy, dysphagia, and gait abnormalities, and we suggested other bases of these phenotypes in French bulldogs that are yet to be discovered. Identification of genes and deleterious variants associated with these clinical signs may assist breeders in improving the overall health of this very popular breed and may lead to the identification of new therapies to reverse muscle atrophy in people and animals with neuromuscular diseases. [ABSTRACT FROM AUTHOR]