A COL11A2 mutation in Labrador retrievers with mild disproportionate dwarfism.

We describe a mild form of disproportionate dwarfism in Labrador Retrievers, which is not associated with any obvious health problems such as secondary arthrosis. We designate this phenotype as skeletal dysplasia 2 (SD2). It is inherited as a monogenic autosomal recessive trait with incomplete penetrance primarily in working lines of the Labrador Retriever breed. Using 23 cases and 37 controls we mapped the causative mutation by genome-wide association and homozygosity mapping to a 4.44 Mb interval on chromosome 12. We re-sequenced the genome of one affected dog at 30x coverage and detected 92 non-synonymous variants in the critical interval. Only two of these variants, located in the lymphotoxin A (LTA) and collagen alpha-2(XI) chain gene (COL11A2), respectively, were perfectly associated with the trait. Previously described COL11A2 variants in humans or mice lead to skeletal dysplasias and/or deafness. The dog variant associated with disproportionate dwarfism, COL11A2:c.143G>C or p.R48P, probably has only a minor effect on collagen XI function, which might explain the comparatively mild phenotype seen in our study. The identification of this candidate causative mutation thus widens the known phenotypic spectrum of COL11A2 mutations. We speculate that non-pathogenic COL11A2 variants might even contribute to the heritable variation in height.

Magnetic resonance imaging and genetic investigation of a case of Rottweiler leukoencephalomyelopathy.

BACKGROUND Leukoencephalomyelopathy is an inherited neurodegenerative disorder that affects the white matter of the spinal cord and brain and is known to occur in the Rottweiler breed. Due to the lack of a genetic test for this disorder, post mortem neuropathological examinations are required to confirm the diagnosis. Leukoencephalopathy with brain stem and spinal cord involvement and elevated lactate levels is a rare, autosomal recessive disorder in humans that was recently described to have clinical features and magnetic resonance imaging (MRI) findings that are similar to the histopathologic lesions that define leukoencephalomyelopathy in Rottweilers. Leukoencephalopathy with brain stem and spinal cord involvement is caused by mutations in the DARS2 gene, which encodes a mitochondrial aspartyl-tRNA synthetase. The objective of this case report is to present the results of MRI and candidate gene analysis of a case of Rottweiler leukoencephalomyelopathy to investigate the hypothesis that leukoencephalomyelopathy in Rottweilers could serve as an animal model of human leukoencephalopathy with brain stem and spinal cord involvement. CASE PRESENTATION A two-and-a-half-year-old male purebred Rottweiler was evaluated for generalised progressive ataxia with hypermetria that was most evident in the thoracic limbs. MRI (T2-weighted) demonstrated well-circumscribed hyperintense signals within both lateral funiculi that extended from the level of the first to the sixth cervical vertebral body. A neurodegenerative disorder was suspected based on the progressive clinical course and MRI findings, and Rottweiler leukoencephalomyelopathy was subsequently confirmed via histopathology. The DARS2 gene was investigated as a causative candidate, but a sequence analysis failed to identify any disease-associated variants in the DNA sequence. CONCLUSION It was concluded that MRI may aid in the pre-mortem diagnosis of suspected cases of leukoencephalomyelopathy. Genes other than DARS2 may be involved in Rottweiler leukoencephalomyelopathy and may also be relevant in human leukoencephalopathy with brain stem and spinal cord involvement.

Congenital proprotein convertase 1/3 deficiency causes malabsorptive diarrhea and other endocrinopathies in a pediatric cohort

BACKGROUND & AIMS Proprotein convertase 1/3 (PC1/3) deficiency, an autosomal-recessive disorder caused by rare mutations in the proprotein convertase subtilisin/kexin type 1 (PCSK1) gene, has been associated with obesity, severe malabsorptive diarrhea, and certain endocrine abnormalities. Common variants in PCSK1 also have been associated with obesity in heterozygotes in several population-based studies. PC1/3 is an endoprotease that processes many prohormones expressed in endocrine and neuronal cells. We investigated clinical and molecular features of PC1/3 deficiency. METHODS We studied the clinical features of 13 children with PC1/3 deficiency and performed sequence analysis of PCSK1. We measured enzymatic activity of recombinant PC1/3 proteins. RESULTS We identified a pattern of endocrinopathies that develop in an age-dependent manner. Eight of the mutations had severe biochemical consequences in vitro. Neonates had severe malabsorptive diarrhea and failure to thrive, required prolonged parenteral nutrition support, and had high mortality. Additional endocrine abnormalities developed as the disease progressed, including diabetes insipidus, growth hormone deficiency, primary hypogonadism, adrenal insufficiency, and hypothyroidism. We identified growth hormone deficiency, central diabetes insipidus, and male hypogonadism as new features of PCSK1 insufficiency. Interestingly, despite early growth abnormalities, moderate obesity, associated with severe polyphagia, generally appears. CONCLUSIONS In a study of 13 children with PC1/3 deficiency caused by disruption of PCSK1, failure of enteroendocrine cells to produce functional hormones resulted in generalized malabsorption. These findings indicate that PC1/3 is involved in the processing of one or more enteric hormones that are required for nutrient absorption.

Estimation of the incidence of a rare genetic disease through a two-tier mutation survey.

Recent attempts to detect mutations involving single base changes or small deletions that are specific to genetic diseases provide an opportunity to develop a two-tier mutation-screening program through which incidence of rare genetic disorders and gene carriers may be precisely estimated. A two-tier survey consists of mutation screening in a sample of patients with specific genetic disorders and in a second sample of newborns from the same population in which mutation frequency is evaluated. We provide the statistical basis for evaluating the incidence of affected and gene carriers in such two-tier mutation-screening surveys, from which the precision of the estimates is derived. Sample-size requirements of such two-tier mutation-screening surveys are evaluated. Considering examples of cystic fibrosis (CF) and medium-chain acyl-CoA dehydrogenase deficiency (MCAD), the two most frequent autosomal recessive disease in Caucasian populations and the two most frequent mutations (delta F508 and G985) that occur on these disease allele-bearing chromosomes, we show that, with 50-100 patients and a 20-fold larger sample of newborns screened for these mutations, the incidence of such diseases and their gene carriers in a population may be quite reliably estimated. The theory developed here is also applicable to rare autosomal dominant diseases for which disease-specific mutations are found.

Mutation analysis of the PVRL1 gene in caucasians with nonsyndromic cleft lip/palate.

Nonsyndromic cleft lip with or without cleft palate (nsCL/P, MIM 119530) is perhaps the most common major birth defect. Homozygous PVRL1 loss-of-function mutations result in an autosomal recessive CL/P syndrome, CLPED1, and a PVRL1 nonsense mutation is associated with sporadic nsCL/P in Northern Venezuela. To address the more general role of PVRL1 variation in risk of nsCL/P, we carried out mutation analysis of PVRL1 in North American and Australian nsCL/P cases and population-matched controls. We identified a total of 15 variants, 5 of which were seen in both populations and 1 of which, an in-frame insertion at Glu442, was more frequent in patients than in controls in both populations, though the difference was not statistically significant. Another variant, which is specific to the PVRL1 beta (HIgR) isoform, S447L, was marginally associated with nsCL/P in North American Caucasian patients, but not in Australian patients, and overall variants that affect the beta-isoform were significantly more frequent among North American patients. One Australian patient had a splice junction mutation of PVRL1. Our results suggest that PVRL1 may play a minor role in susceptibility to the occurrence of nsCL/P in some Caucasian populations, and that variation involving the beta (HIgR) isoform might have particular importance for risk of orofacial clefts. Nevertheless, these results underscore the need for studies that involve very large numbers when assessing the possible role of rare variants in risk of complex traits such as nsCL/P.

Crystal structure of the alpha(6)beta(6) holoenzyme of propionyl-coenzyme A carboxylase.

Propionyl-coenzyme A carboxylase (PCC), a mitochondrial biotin-dependent enzyme, is essential for the catabolism of the amino acids Thr, Val, Ile and Met, cholesterol and fatty acids with an odd number of carbon atoms. Deficiencies in PCC activity in humans are linked to the disease propionic acidaemia, an autosomal recessive disorder that can be fatal in infants. The holoenzyme of PCC is an alpha(6)beta(6) dodecamer, with a molecular mass of 750 kDa. The alpha-subunit contains the biotin carboxylase (BC) and biotin carboxyl carrier protein (BCCP) domains, whereas the beta-subunit supplies the carboxyltransferase (CT) activity. Here we report the crystal structure at 3.2-A resolution of a bacterial PCC alpha(6)beta(6) holoenzyme as well as cryo-electron microscopy (cryo-EM) reconstruction at 15-A resolution demonstrating a similar structure for human PCC. The structure defines the overall architecture of PCC and reveals unexpectedly that the alpha-subunits are arranged as monomers in the holoenzyme, decorating a central beta(6) hexamer. A hitherto unrecognized domain in the alpha-subunit, formed by residues between the BC and BCCP domains, is crucial for interactions with the beta-subunit. We have named it the BT domain. The structure reveals for the first time the relative positions of the BC and CT active sites in the holoenzyme. They are separated by approximately 55 A, indicating that the entire BCCP domain must translocate during catalysis. The BCCP domain is located in the active site of the beta-subunit in the current structure, providing insight for its involvement in the CT reaction. The structural information establishes a molecular basis for understanding the large collection of disease-causing mutations in PCC and is relevant for the holoenzymes of other biotin-dependent carboxylases, including 3-methylcrotonyl-CoA carboxylase (MCC) and eukaryotic acetyl-CoA carboxylase (ACC).

A molecular study of the rhodopsin locus in patients with retinitis pigmentosa

DNA for this study was collected from a sample of 133 retinitis pigmentosa (RP) patients and the rhodopsin locus molecularly analyzed by linkage and for disease specific mutations. The cohort of patients consisted of 85 individuals diagnosed with autosomal dominant RP (adRP), and 48 patients representing other forms of retinitis pigmentosa or retinal dystrophy related disease. In three large families with adRP rhodopsin was excluded from linkage to the disease locus. A search for subtle mutations in the rhodopsin coding region using single strand conformational polymorphisms (SSCP) and sequencing detected a total of 14 unique sequence variants in 24 unrelated patients. These variants included one splicing variant, 5168 -1G-A, one deletion variant of 17 base pairs causing a frame shift at codon 332, and 12 misense variants: Pro23His, Leu46Arg, Gly106Trp, Arg135Pro, Pro171Glu, Pro180Ala, Glu181Lys, Asp190Asn, His211Arg, Ser270Arg, Leu328Pro and Pro347Thr. All but three of the missense variants change amino acids that are evolutionarily conserved. The Pro23His mutation was found in 10 unrelated individuals with family histories of adRP and not in any normal controls (over 80 chromosomes tested). The Pro180Ala mutation was present in a patient with simplex RP and probably represents a new mutation. Three normal polymorphic nucleotide substitutions, A-269-G, T-3982-C, and G-5145-A, were also identified. We conclude, based on this study, that 25% of adRP cases are attributable to rhodopsin mutations.^ Clinical data, including ERG results and visual field testing, was available for patients with eleven different mutations. The eleven patients were all diagnosed with RP, however the severity of the disease varied with five patients mildly affected and diagnosed with type II adRP and 5 patients severely affected and diagnosed with type I adRP. The patient with simplex RP was mildly affected. The location of the mutations within the rhodopsin protein was randomly associated with the severity of the disease in those patients evaluated. However, four mutations, Pro23His, Leu46Arg, Pro347Thr, and 5168 -1G-A, are particularly interesting. The Pro23His mutation appears to have radiated from a recent common ancestor of the affected patients as all of them share a common haplotype at the rhodopsin locus. The Leu46Arg mutation causes an unusually severe form of RP. Hydropathy analysis of the mutated sequence revealed a marked change in the hydrophobicity of this first transmembrane spanning region. Codon 347 has been the target of multiple mutations with at least six documented changes at the position, significantly more than expected by a random distribution of mutations. Finally the splice-site variant is extremely variable in its expression in the family studied. Similar mutations have been reported in other cases of adRP and postulated to be involved in autosomal recessive RP (arRP). Mechanisms to account for the variable expression of rhodopsin mutations in relation to RP heterogeneity are discussed. (Abstract shortened by UMI.) ^

Characterization of a novel CYP19A1 (aromatase) R192H mutation causing virilization of a 46,XX newborn, undervirilization of the 46,XY brother, but no virilization of the mother during pregnancies.

BACKGROUND P450 aromatase (CYP19A1) is essential for the biosynthesis of estrogens from androgen precursors. Mutations in the coding region of CYP19A1 lead to autosomal recessive aromatase deficiency. To date over 20 subjects have been reported with aromatase deficiency which may manifest during fetal life with maternal virilization and virilization of the external genitalia of a female fetus due to low aromatase activity in the steroid metabolizing fetal-placental unit and thus high androgen levels. During infancy, girls often have ovarian cysts and thereafter fail to enter puberty showing signs of variable degree of androgen excess. Moreover, impact on growth, skeletal maturation and other metabolic parameters is seen in both sexes. OBJECTIVE AND HYPOTHESIS We found a novel homozygous CYP19A1 mutation in a 46,XX girl who was born at term to consanguineous parents. Although the mother did not virilize during pregnancy, the baby was found to have a complex genital anomaly at birth (enlarged genital tubercle, fusion of labioscrotal folds) with elevated androgens at birth, normalizing thereafter. Presence of 46,XX karyotype and female internal genital organs (uterus, vagina) together with biochemical findings and follow-up showing regression of clitoral hypertrophy, as well as elevated FSH suggested aromatase deficiency. Interestingly, her older brother presented with mild hypospadias and bilateral cryptorchidism and was found to carry the same homozygous CYP19A1 mutation. To confirm the clinical diagnosis, genetic, functional and computational studies were performed. METHODS AND RESULTS Genetic analysis revealed a homozygous R192H mutation in the CYP19A1 gene. This novel mutation was characterized for its enzymatic activity (Km, Vmax) in a cell model and found to have markedly reduced catalytic activity when compared to wild-type aromatase; thus explaining the phenotype. Computational studies suggest that R192H disrupts the substrate access channel in CYP19A1 that may affect binding of substrates and exit of catalytic products. CONCLUSION R192H is a novel CYP19A1 mutation which causes a severe phenotype of aromatase deficiency in a 46,XX newborn and maybe hypospadias and cryptorchidism in a 46,XY, but no maternal androgen excess during pregnancy.

How useful is the ultrastructural study of the cilia of the respiratory tract in the diagnosis of an immotile cilia syndrome?

The immotile cilia syndrome (ICS) comprises a range of congenital defects of the ciliary apparatus most probably transmitted by autosomal recessive inheritance. Because cilia occur mainly in the respiratory and genital tract, the clinical symptoms of ICS are most commonly chronic sinusitis, bronchitis, bronchiectasis and male sterility. The syndrome can be associated with a situs inversus and is then called Kartagener's syndrome. We studied the ciliary ultrastructure in airway biopsies of 5 patients suffering from chronic upper and lower respiratory tract infections. With the single exception of one female patient with confirmed ICS diagnosis (Kartagener's syndrome) the etiology of the recurrent infections was unknown. The following ciliary defects were observed: missing dynein arms, radial spoke defects, missing nexin links, microtubular transpositions, compound cilia, supernumerary, absent, or incomplete microtubules, lack of ciliary orientation and various abnormal patterns of microtubular arrangement. In no instance did a patient show only a single anomaly; defects were always combined. Missing dynein arms, radial spoke defects and microtubular transpositions have frequently been described as lesions specific for ICS. Whenever these lesions were found simultaneously in both the respiratory and genital tracts, their genetic origin cannot be doubted. In our confirmed ICS patient the outer dynein arms were not missing but were reduced in number and length in a large number of cilia. The biopsy was, however, obtained from the heavily infected maxillary sinus and it is known that inflammation can lead to a loss of dynein arms. In the light of our investigations and of a review of the published cases of ciliary anomalies, it is concluded that none of the above defects in itself is specific for ICS. They may all occur as secondary lesions or sporadically as varieties in otherwise healthy subjects. It therefore appears questionable whether ICS can be diagnosed from the ciliary ultrastructure of a single airway biopsy. Assessment of ICS cannot be based simply on the ultrastructural demonstration of a particular ciliary defect, but necessitates additional considerations particularly regarding the origin of the biopsy, the sampling procedures and quantitation of defects. It appears necessary to investigate samples from different parts of the airways and quantitatively analyze the prominent lesions.

Incomplete Distal Renal Tubular Acidosis from a Heterozygous Mutation of the V-ATPase B1 Subunit

Congenital distal renal tubular acidosis (dRTA) from mutations of the B1 subunit of the V-ATPase is considered an autosomal recessive disease. We analyzed a dRTA kindred with a truncation-mutation of B1 (p.Phe468fsX487) previously shown to have failure of assembly into the V1 domain of the V-ATPase. All heterozygous carriers in this kindred have normal plasma bicarbonate concentrations, thus evaded the diagnosis of RTA. However, inappropriately high urine pH, hypocitraturia, and hypercalciuria are present either individually or in combination in the heterozygotes at baseline. Two of the heterozygotes studied also have inappropriate urinary acidification with acute ammonium chloride loading and impaired urine-blood pCO2 gradient during bicarbonaturia indicating presence of H+ gradient and flux defects. In normal human renal papillae, wild type B1 is located primarily on the plasma membrane but papilla from one of the heterozygote who had kidney stones had renal tissue secured from surgery showed B1 in both plasma membrane as well as a diffuse intracellular staining. Titrating increasing amounts of the mutant B1 subunit did not exhibit negative dominance over the expression, cellular distribution, or H+-pump activity of the wild type B1 in mammalian HEK293 cells and in V-ATPase-deficient S. cerevisiae. This is the first demonstration of renal acidification defects and nephrolithiasis in heterozygous carriers of mutant B1 subunit; which cannot be attributable to negative dominance. We propose that heterozygosity may lead to mild real acidification defects due to haploinsufficiency. B1 heterozygosity should be considered in patients with calcium nephrolithiasis and urinary abnormalities such as alkalinuria or hypocitraturia.

Congenital Hepatic Fibrosis in the Franches-Montagnes Horse Is Associated with the Polycystic Kidney and Hepatic Disease 1 (PKHD1) Gene

Congenital hepatic fibrosis has been described as a lethal disease with monogenic autosomal recessive inheritance in the Swiss Franches-Montagnes horse breed. We performed a genome-wide association study with 5 cases and 12 controls and detected an association on chromosome 20. Subsequent homozygosity mapping defined a critical interval of 952 kb harboring 10 annotated genes and loci including the polycystic kidney and hepatic disease 1 (autosomal recessive) gene (PKHD1). PKHD1 represents an excellent functional candidate as variants in this gene were identified in human patients with autosomal recessive polycystic kidney and hepatic disease (ARPKD) as well as several mouse and rat mutants. Whereas most pathogenic PKHD1 variants lead to polycystic defects in kidney and liver, a small subset of the human ARPKD patients have only liver symptoms, similar to our horses with congenital hepatic fibrosis. The PKHD1 gene is one of the largest genes in the genome with multiple alternative transcripts that have not yet been fully characterized. We sequenced the genomes of an affected foal and 46 control horses to establish a comprehensive list of variants in the critical interval. We identified two missense variants in the PKHD1 gene which were strongly, but not perfectly associated with congenital hepatic fibrosis. We speculate that reduced penetrance and/or potential epistatic interactions with hypothetical modifier genes may explain the imperfect association of the detected PKHD1 variants. Our data thus indicate that horses with congenital hepatic fibrosis represent an interesting large animal model for the liver-restricted subtype of human ARPKD.

A mutation in the FAM83G gene in dogs with hereditary footpad hyperkeratosis (HFH)

Hereditary footpad hyperkeratosis (HFH) represents a palmoplantar hyperkeratosis, which is inherited as a monogenic autosomal recessive trait in several dog breeds, such as e.g. Kromfohrländer and Irish Terriers. We performed genome-wide association studies (GWAS) in both breeds. In Kromfohrländer we obtained a single strong association signal on chromosome 5 (p(raw) = 1.0×10(-13)) using 13 HFH cases and 29 controls. The association signal replicated in an independent cohort of Irish Terriers with 10 cases and 21 controls (p(raw) = 6.9×10(-10)). The analysis of shared haplotypes among the combined Kromfohrländer and Irish Terrier cases defined a critical interval of 611 kb with 13 predicted genes. We re-sequenced the genome of one affected Kromfohrländer at 23.5× coverage. The comparison of the sequence data with 46 genomes of non-affected dogs from other breeds revealed a single private non-synonymous variant in the critical interval with respect to the reference genome assembly. The variant is a missense variant (c.155G>C) in the FAM83G gene encoding a protein with largely unknown function. It is predicted to change an evolutionary conserved arginine into a proline residue (p.R52P). We genotyped this variant in a larger cohort of dogs and found perfect association with the HFH phenotype. We further studied the clinical and histopathological alterations in the epidermis in vivo. Affected dogs show a moderate to severe orthokeratotic hyperplasia of the palmoplantar epidermis. Thus, our data provide the first evidence that FAM83G has an essential role for maintaining the integrity of the palmoplantar epidermis.

Polycystic Kidneys and GM2 Gangliosidosis-Like Disease in Neonatal Springboks (Antidorcas marsupialis)

Clinical, gross, histopathologic, electron microscopic findings and enzymatic analysis of 4 captive, juvenile springboks (Antidorcas marsupialis) showing both polycystic kidneys and a storage disease are described. Springbok offspring (4 of 34; 12%) were affected by either one or both disorders in a German zoo within a period of 5 years (2008-2013). Macroscopic findings included bilaterally severely enlarged kidneys displaying numerous cysts in 4 animals and superior brachygnathism in 2 animals. Histopathologically, kidneys of 4 animals displayed cystic dilation of the renal tubules. In addition, abundant cytoplasmic vacuoles with a diameter ranging from 2 to 10 μm in neurons of the central and peripheral nervous system, hepatocytes, thyroid follicular epithelial cells, pancreatic islets of Langerhans and renal tubular cells were found in 2 springbok neonates indicative of an additional storage disease. Ultrastructurally, round electron-lucent vacuoles, up to 4 μm in diameter, were present in neurons. Enzymatic analysis of liver and kidney tissue of 1 affected springbok revealed a reduced activity of total hexosaminidase (Hex) with relatively increased HexA activity at the same level of total Hex, suggesting a hexosaminidase defect. Pedigree analysis suggested a monogenic autosomal recessive inheritance for both diseases. In summary, related springboks showed 2 different changes resembling both polycystic kidney and a GM2 gangliosidosis similar to the human Sandhoff disease. Whether the simultaneous occurrence of these 2 entities represents an incidental finding or has a genetic link needs to be investigated in future studies.

In vitro rescue of FGA deletion by lentiviral transduction of an afibrinogenemic patient's hepatocytes.

BACKGROUND: Congenital afibrinogenemia is a rare inherited autosomal recessive disorder in which a mutation in one of three genes coding for the fibrinogen polypeptide chains Aα, Bβ and γ results in the absence of a functional coagulation protein. A patient with congenital afibrinogenemia, resulting from an FGA homozygous gene deletion, underwent an orthotopic liver transplant that resulted in complete restoration of normal hemostasis. The patient's explanted liver provided a unique opportunity to further investigate a potential novel treatment modality. OBJECTIVE: To explore a targeted gene therapy approach for patients with congenital afibrinogenemia. METHODS AND RESULTS: At the time of transplant, the patient's FGA-deficient hepatocytes were isolated and transduced with lentiviral vectors encoding the human fibrinogen Aα-chain. FGA-transduced hepatocytes produced fully functional fibrinogen in vitro. CONCLUSIONS: Orthotopic liver transplantation is a possible rescue treatment for failure of on-demand fibrinogen replacement therapy. In addition, we provide evidence that hepatocytes homozygous for a large FGA deletion can be genetically modified to restore Aα-chain protein expression and secrete a functional fibrinogen hexamer.

A Deletion in the VLDLR Gene in Eurasier Dogs with Cerebellar Hypoplasia Resembling a Dandy-Walker-Like Malformation (DWLM).

Dandy-Walker-like malformation (DWLM) is the result of aberrant brain development and mainly characterized by cerebellar hypoplasia. DWLM affected dogs display a non-progressive cerebellar ataxia. Several DWLM cases were recently observed in the Eurasier dog breed, which strongly suggested a monogenic autosomal recessive inheritance in this breed. We performed a genome-wide association study (GWAS) with 9 cases and 11 controls and found the best association of DWLM with markers on chromosome 1. Subsequent homozygosity mapping confirmed that all 9 cases were homozygous for a shared haplotype in this region, which delineated a critical interval of 3.35 Mb. We sequenced the genome of an affected Eurasier and compared it with the Boxer reference genome and 47 control genomes of dogs from other breeds. This analysis revealed 4 private non-synonymous variants in the critical interval of the affected Eurasier. We genotyped these variants in additional dogs and found perfect association for only one of these variants, a single base deletion in the VLDLR gene encoding the very low density lipoprotein receptor. This variant, VLDLR:c.1713delC is predicted to cause a frameshift and premature stop codon (p.W572Gfs*10). Variants in the VLDLR gene have been shown to cause congenital cerebellar ataxia and mental retardation in human patients and Vldlr knockout mice also display an ataxia phenotype. Our combined genetic data together with the functional knowledge on the VLDLR gene from other species thus strongly suggest that VLDLR:c.1713delC is indeed causing DWLM in Eurasier dogs.