Kennel Club Genetics Centre, Animal Health Trust, Kentford, Newmarket, Suffolk, CB8 7UU, UK.
BMC Genet. 2012 Jul 10;13:55. doi: 10.1186/1471-2156-13-55.
Neonatal cerebellar cortical degeneration is a neurodegenerative disease described in several canine breeds including the Beagle. Affected Beagles are unable to ambulate normally from the onset of walking and the main pathological findings include Purkinje cell loss with swollen dendritic processes. Previous reports suggest an autosomal recessive mode of inheritance. The development of massively parallel sequencing techniques has presented the opportunity to investigate individual clinical cases using genome-wide sequencing approaches. We used genome-wide mRNA sequencing (mRNA-seq) of cerebellum tissue from a single Beagle with neonatal cerebellar cortical degeneration as a method of candidate gene sequencing, with the aim of identifying the causal mutation.
A four-week old Beagle dog presented with progressive signs of cerebellar ataxia and the owner elected euthanasia. Histopathology revealed findings consistent with cerebellar cortical degeneration. Genome-wide mRNA sequencing (mRNA-seq) of RNA from cerebellum tissue was used as a method of candidate gene sequencing. After analysis of the canine orthologues of human spinocerebellar ataxia associated genes, we identified a homozygous 8 bp deletion in the β-III spectrin gene, SPTBN2, associated with spinocerebellar type 5 in humans. Genotype analysis of the sire, dam, ten clinically unaffected siblings, and an affected sibling from a previous litter, showed the mutation to fully segregate with the disorder. Previous studies have shown that β-III spectrin is critical for Purkinje cell development, and the absence of this protein can lead to cell damage through excitotoxicity, consistent with the observed Purkinje cell loss, degeneration of dendritic processes and associated neurological dysfunction in this Beagle.
An 8 bp deletion in the SPTBN2 gene encoding β-III spectrin is associated with neonatal cerebellar cortical degeneration in Beagle dogs. This study shows that mRNA-seq is a feasible method of screening candidate genes for mutations associated with rare diseases when a suitable tissue resource is available.
新生儿小脑皮质变性是一种神经退行性疾病，在包括比格犬在内的几种犬种中都有描述。受影响的比格犬从开始行走时就无法正常行走，主要的病理发现包括浦肯野细胞丢失和肿胀的树突状突起。以前的报告表明其为常染色体隐性遗传方式。大规模并行测序技术的发展为使用全基因组测序方法研究个别临床病例提供了机会。我们使用了一只患有新生儿小脑皮质变性的比格犬的小脑组织的全基因组 mRNA 测序（mRNA-seq）作为候选基因测序的方法，目的是确定致病突变。
一只四周大的比格犬出现进行性小脑共济失调症状，其主人选择了安乐死。组织病理学检查发现与小脑皮质变性一致的发现。我们使用小脑组织的全基因组 mRNA 测序（mRNA-seq）作为候选基因测序的方法。在分析与人类脊髓小脑共济失调相关的人类同源基因后，我们在β-III spectrin 基因 SPTBN2 中发现了一个与人类脊髓小脑型 5 型相关的 8 bp 缺失的纯合子。对父亲、母亲、十个临床无影响的兄弟姐妹以及前一窝受影响的兄弟姐妹进行基因型分析，显示该突变与该疾病完全分离。以前的研究表明，β-III spectrin 对浦肯野细胞的发育至关重要，这种蛋白的缺失可导致通过兴奋毒性引起细胞损伤，这与该比格犬中观察到的浦肯野细胞丢失、树突状突起退化以及相关的神经功能障碍一致。
SPTBN2 基因编码的β-III spectrin 中的 8 bp 缺失与比格犬的新生儿小脑皮质变性有关。本研究表明，当有合适的组织资源时，mRNA-seq 是筛查与罕见疾病相关的突变的候选基因的可行方法。
