Novel COL6A3 frameshift variant in American Staffordshire Terrier dogs with Ullrich-like congenital muscular dystrophy

Abstract

Two (male and female) 10-month-old American Staffordshire Terrier littermates presented for progressive weakness, joint contracture, and distal limb joint hyperlaxity beginning around 6 months of age. Neurological examination, serum creatine kinase activity, infectious disease titers, cerebrospinal fluid analysis, and electrodiagnostic testing were performed. Muscle biopsies were collected for histopathology and immunofluorescence staining for localization of dystrophy associated proteins. Whole-genome sequencing (WGS) was performed on 1 affected dog. Variants were compared to a database of 671 unaffected dogs of multiple breeds. Histopathology confirmed a dystrophic phenotype and immunofluorescence staining of muscle cryosections revealed an absence of staining for collagen-6. WGS identified a homozygous 1 bp deletion in the COL6A3 gene, unique to the first affected dog. Sanger sequencing confirmed the homozygous presence of the frameshift variant in both affected dogs. This report describes the clinical features and most likely genetic basis of an Ullrich-like recessively inherited form of congenital muscular dystrophy in American Staffordshire Terriers.

Keywords: collagen; joint laxity; myopathy; sequencing.

FIGURE 1

Abnormal posture displayed by 2 juvenile Staffordshire terrier dogs with Ullrich‐like congenital muscular dystrophy. Note the kyphosis, partial contracture of the carpi, and hyperextension of the tarsi, metatarsophalangeal, and metacarpophalangeal joints.

FIGURE 2

Cryosections from the vastus lateralis muscles of Cases 1 and 2 showed similar pathological changes including excessive variability in myofiber size with scattered atrophic fibers having a round shape, fibers containing internal nuclei, sporadic necrotic fibers undergoing phagocytosis, and mild endomysial fibrosis. H&E and trichrome stains. Bar in lower right corner of all images = 100 μm.

FIGURE 3

Immunofluorescence staining of the vastus lateralis muscle from Cases 1 and 2, and an archived control muscle, stained with antibodies against laminin α2, collagen‐6 and the rod domain of dystrophin. Staining for collagen‐6 was absent in Cases 1 and 2 and showed a normal staining pattern in the archived control muscle. Staining for laminin α2 and the rod domain of dystrophin was similar to control in both cases. Bar in lower right image = 50 μm for all images.

FIGURE 4

COL6A3 1 bp deletion (chr25:48287602CG>C, c.6398del p.Pro2133ArgfsTer109) detected with whole‐genome sequencing. A 91 bp region flanking exon 21 is shown in the case (upper) and a control (lower) dog aligned to CanFam4. The (*) in the case dog indicates the location of the deleted nucleotide.