Congenital recessive malformation of the axial skeleton that drastically shortens the trunk and produces hemivertebrae and rib anomalies (fusion, misalignment, reduced number), giving the puppy a 'comma' contour. Most affected animals are stillborn or die within the first hours or days of life. It may be accompanied by umbilical hernia and cleft palate. It is the canine analogue of human spondylocostal dysostosis caused by HES7.

Characterised in Miniature Schnauzers in Australia. The mutation was not detected in 117 Miniature Schnauzers or in 6 Standard Schnauzers analysed outside the index family; global dispersal through stud dogs of distant geographic origin is suspected. Population frequency data are limited.

- Marked shortening of the trunk at birth\n- Hindquarters relatively hypoplastic compared with the forequarters\n- Multiple hemivertebrae and fused, misaligned or reduced-number ribs\n- 'Comma' body contour\n- Possible umbilical hernia and cleft palate\n- Stillborn or death within the first hours or days

The 'Comma' defect was described in Australia in an outbred Miniature Schnauzer family with puppies stillborn or with neonatal death and a shortened 'comma' contour. Willet and colleagues (2015) characterised it by computed tomography, demonstrating that it reproduces human spondylocostal dysostosis. Mapping and whole-genome sequencing identified a deletion of one guanine in the coding region of HES7 (c.126delG) that produces a frameshift (p.Thr43ProfsTer24) and removes domains essential for the oscillatory autorepression of HES7 during somitogenesis. The mutation was not observed in 117 randomly sampled adult Miniature Schnauzers or in 6 adult Standard Schnauzers, but it could be distributed globally through unrelated stud dogs from distant regions.

- Test breeding animals with the HES7 test, especially in lines with a history of stillbirths or malformed puppies\n- Do not cross two carriers: 25% affected homozygotes (stillborn or neonates that die)\n- A carrier may be mated with a clear animal; offspring intended for breeding must be tested\n- In a litter with shortened puppies or stillbirths, suspect the Comma defect and confirm genetically before continuing the line\n- Progressively replace carriers with clear offspring without narrowing the gene pool

The differential diagnosis of stillbirths with trunk shortening includes other dysostoses, congenital diaphragmatic hernias and neural tube closure defects. Tomography allows the vertebral and rib anomalies to be visualised before attributing the condition to the Comma defect. It is important that the breeder reports malformed stillbirths, since the defect may go unnoticed. The HES7 mutation is validated in the Miniature Schnauzer; the test is also offered for the Schnauzer breed as a whole.

1. Willet CE, Makara M, Reppas G, et al. Canine disorder mirrors human disease: exonic deletion in HES7 causes autosomal recessive spondylocostal dysostosis in miniature Schnauzer dogs. PLoS One. 2015;10(2):e0117055. PMID: 25659135