Canine Disorder Mirrors Human Disease: Exonic Deletion in <i>HES7</i> Causes Autosomal Recessive Spondylocostal Dysostosis in Miniature Schnauzer Dogs

<div><p>Spondylocostal dysostosis is a congenital disorder of the axial skeleton documented in human families from diverse racial backgrounds. The condition is characterised by truncal shortening, extensive hemivertebrae and rib anomalies including malalignment, fusion and reduction in number. Mutations in the Notch signalling pathway genes <i>DLL3</i>, <i>MESP2</i>, <i>LFNG</i>, <i>HES7</i> and <i>TBX6</i> have been associated with this defect. In this study, spondylocostal dysostosis in an outbred family of miniature schnauzer dogs is described. Computed tomography demonstrated that the condition mirrors the skeletal defects observed in human cases, but unlike most human cases, the affected dogs were stillborn or died shortly after birth. Through gene mapping and whole genome sequencing, we identified a single-base deletion in the coding region of <i>HES7</i>. The frameshift mutation causes loss of functional domains essential for the oscillatory transcriptional autorepression of HES7 during somitogenesis. A restriction fragment length polymorphism test was applied within the immediate family and supported a highly penetrant autosomal recessive mode of inheritance. The mutation was not observed in wider testing of 117 randomly sampled adult miniature schnauzer and six adult standard schnauzer dogs; providing a significance of association of <i>P</i>_raw = 4.759e^-36 (genome-wide significant). Despite this apparently low frequency in the Australian population, the allele may be globally distributed based on its presence in two unrelated sires from geographically distant locations. While isolated hemivertebrae have been observed in a small number of other dog breeds, this is the first clinical and genetic diagnosis of spontaneously occurring spondylocostal dysostosis in a non-human mammal and offers an excellent model in which to study this devastating human disorder. The genetic test can be utilized by dog breeders to select away from the disease and avoid unnecessary neonatal losses.</p></div

Significantly associated SNPs with dEBV for height at withers using a mixed-model approach.

a<p>EquCab 2.0 assembly.</p>b<p>corresponding homologous human position, build 37.</p>c<p>trait-increasing allele/trait-decreasing allele; (frequency of the trait-increasing allele).</p>d<p>corresponding list of p-values of 1-d.f. (additive or allelic) test for association between SNP and trait; the Bonferroni-corrected threshold for a 5% genome-wide significance level is p_BONF = 1.31×10⁻⁶.</p>e<p>corresponding list of empirical p-values derived from permutations with 40,000 replicates.</p

Distribution of EBVs and dEBVs for conformation traits in FM horses.

a<p>Minimum and maximum estimated breeding values (EBV). The average estimated breeding value for animals born between 1998 and 2000 was set to 0.</p>b<p>Minimum and maximum deregressed breeding values (dEBV). Deregressed EBVs were used for association analysis.</p

Combined effect size of the two identified QTL on ECA 3 and ECA 9 on the dEBV for height at withers in the FM horse breed.

<p>The box plot indicates the median values, 25% and 75% quartiles and the outliers of the distribution. A total of 308, 513, 211, and 21 animals, respectively, represented the classes from zero to three trait-increasing alleles. The difference in the medians between horses with zero and three trait-increasing alleles, respectively, is 2.97 cm. None of the analyzed horses carried four trait-increasing alleles. The association between the number of trait increasing alleles and height at withers is highly significant (p = 8.4×10⁻¹³; Kruskal-Wallis test). Medians are significantly different between groups.</p

The Franches-Montagnes horse belongs to the type of light draft horse breeds and has its origins in Switzerland (A).

<p>Height at withers is one of 28 conformation traits, for which breeding values are estimated once a year (B). The breed standard calls for horses between 150–160 cm in size. The stallion in the background was the tallest horse in our study with a phenotypic height at withers of 165 cm. (Picture: Swiss National Stud Farm).</p

Manhattan plot for height at withers based on dEBV.

<p>The red line indicates the Bonferroni-corrected significance level (p<1.31×10⁻⁶). The inset shows a quantile-quantile (qq) plot with the observed plotted against the expected p-values. The used mixed-model approach efficiently corrected for the stratification in the sample. The skew at the right edge indicates that these SNPs are stronger associated with height than would be expected by chance. This is consistent with a true association as opposed to a false positive signal due to population stratification.</p

Genome-wide association analysis for Comma defect.

<p>The analysis included three cases and seven controls genotyped on the Canine HD BeadChip. Coordinates shown are from the canFam2 assembly. (a) Haploview plot of -log₁₀ transformed <i>P</i> values for 73,921 SNPs tested for association using PLINK. (b) Haploview plot of -log₁₀ transformed <i>P</i> values for SNPs on CFA5.</p

Comma defect PCR-RFLP test results for 11 miniature schnauzers.

<p>Samples in lanes 1–9 are homozygous for the wild-type genotype; lane 10 shows a carrier for the deletion; lane 11 is homozygous for the mutant allele. L = ladder (100 bp).</p

Effect of different QTL genotypes on the dEBV height at withers.

a<p>The mean dEBV for the homozygous trait-decreasing genotype was arbitrarily set to zero. The values correspond to centimeters.</p

CT scans of miniature schnauzer pups affected with Comma defect and an age-matched unrelated control.

<p>(a) Unaffected Nova Scotia duck tolling retriever pup sampled for unrelated reasons. (b) Affected miniature schnauzer pup USCF134. (c) Affected miniature schnauzer pup USCF136. (d) Affected miniature schnauzer pup USCF137.</p