PMC

(A) A Schematic representation of the SEL1L protein, which shows the multi-modular protein structure. The p.Ser658Pro mutation hits one of the C-terminal Sel1-repeats. (B) SEL1L amino acid sequence alignment. Position of the mutation is conserved in all aligned species except for C. elegans and yeast. The Hrd3-motif, which is positioned five residues downstream from the Ser658, shows conservation across all aligned species.

Pedigree shows those affected litters that were used in the study. Disease segregation is consistent with autosomal recessive mode of inheritance as all affected dogs are born from healthy parents and both sexes are affected. The proportion of affected puppies is 29%, which is close to expected 25%. Denoted are the clinically and pathologically examined cases and the dogs that were genotyped for genome-wide analyses. The numbering of litters and puppies refers to the numbering used in . *In this one litter, the total number of offspring was unknown.

Sagittal midline T2W brain MRI images of a normal and affected Finnish Hounds. (A) A control dog with normal cerebellum (arrow). (B) An affected dog that has smaller cerebellar size and increased cerebrospinal fluid space (white) between the cerebellum and the occipital bone ventrally (arrow). (C) An affected dog that shows reduced cerebellar size and increase in the fluid filled space in the area of the fourth ventricle (arrow). (D) Another affected dog that has reduced cerebellar size and increased fluid filled spaces between the cerebellar folia (arrows).

(A) The mRNA levels of SEL1L, STON2 and CEP128 in the cerebellar cortex of five affected dogs compared to a control puppy. These three genes had sequence variants that segregated with the ataxia phenotype. (B) Endoplasmic reticulum (ER) stress markers are upregulated in the cerebellar cortex of affected animals. The relative mRNA expression levels are represented as a fold change. Error bars denote the standard error of normalized Ct-values. *p≤0.05 **p≤0.001 ***p≤0.000 (two-tailed t-test p-values).

(A) A Manhattan plot of case-control genome-wide association test performed using 13 cases and 7 unaffected sibling-controls. (B) Results of the family-based testing on the disease associated chromosome 8. Plotted are single-point linkage analysis LOD scores, association test p-values and joint analysis p-values. (C) Genotypes at the disease associated locus on CFA8. All cases share a 1.5 Mb homozygous block, and within this block BICF2P948919 shows complete segregation with the disease. (D) A schematic representation of the seven genes found on the 1.5 Mb block and of the SEL1L gene structure. SEL1L exons are marked with black boxes and red denotes the untranslated regions (UTRs). BICF2P948919 is located on second SEL1L intron and the c.1972T>C mutation on exon 19. (E) Chromatograms of the c.1972T>C mutation in an affected, a carrier and a wild-type dog.

(A) Normal cerebellar cortex in the ventrolateral parts of the cerebellum, with densely cellular granular cell layer (HE 100×). (B) Affected cerebellar cortex in the vermal region with marked loss of granular cells (HE 100×). (C) A higher magnification of unaffected cortex with viable Purkinje cells (PCs) and a normal granular cell density (HE 400×). (D) A higher magnification of affected cortex, with severe loss of PCs and linear reactive gliosis between the molecular and the granular layers (arrow) (HE 400×). (E) Degenerating, shrunken, eosinophilic PCs with margination of the nuclear chromatin (black arrow) or central chromatolysis of the cytoplasma (red arrow) (HE 400×). (F) PCs that show total loss of cytoplasmic basophilia (Nissl substance) and pyknotic or karyorhektic nuclei (arrows). Inset: viable PC with intact Nissl substance seen as basophilic cytoplasmic granulation (LFB-CEV, 400×). (G) Left: mild astrogliosis (arrows) within the granular cell layer and the white matter of the cerebellar folia. Right: unaffected part of same dog (IHC GFAP, 400×). (H) Left: secondary degeneration and myelinophagia in the affected cerebellar white matter. Right: unaffected parts of same dog (LFB-CEV, 400×). ML = molecular layer, PL = Purkinje cell layer, GL = granular cell layer, WM = white matter.