MKLN1 splicing defect in dogs with lethal acrodermatitis

Lethal acrodermatitis (LAD) is a genodermatosis with monogenic autosomal recessive inheritance in Bull Terriers and Miniature Bull Terriers. The LAD phenotype is characterized by poor growth, immune deficiency, and skin lesions, especially at the paws. Utilizing a combination of genome wide association study and haplotype analysis, we mapped the LAD locus to a critical interval of ~1.11 Mb on chromosome 14. Whole genome sequencing of an LAD affected dog revealed a splice region variant in the MKLN1 gene that was not present in 191 control genomes (chr14:5,731,405T>G or MKLN1:c.400+3A>C). This variant showed perfect association in a larger combined Bull Terrier/Miniature Bull Terrier cohort of 46 cases and 294 controls. The variant was absent from 462 genetically diverse control dogs of 62 other dog breeds. RT-PCR analysis of skin RNA from an affected and a control dog demonstrated skipping of exon 4 in the MKLN1 transcripts of the LAD affected dog, which leads to a shift in the MKLN1 reading frame. MKLN1 encodes the widely expressed intracellular protein muskelin 1, for which diverse functions in cell adhesion, morphology, spreading, and intracellular transport processes are discussed. While the pathogenesis of LAD remains unclear, our data facilitate genetic testing of Bull Terriers and Miniature Bull Terriers to prevent the unintentional production of LAD affected dogs. This study may provide a starting point to further clarify the elusive physiological role of muskelin 1 in vivo.

致死性肢端皮炎（Lethal acrodermatitis, LAD）是一种单基因常染色体隐性遗传的遗传性皮肤病，仅见于斗牛㹴（Bull Terrier）与迷你斗牛㹴（Miniature Bull Terrier）。该疾病的LAD表型以生长发育迟缓、免疫缺陷以及皮肤损伤为主要特征，尤其好发于四肢末端。本研究结合全基因组关联分析与单倍型分析，将LAD致病位点定位至犬14号染色体上约1.11 Mb的关键区间内。对一只患LAD的犬进行全基因组测序后，发现其MKLN1基因存在一处剪接区变异，该变异在191份对照犬基因组中均未检出（chr14:5,731,405T>G 或 MKLN1:c.400+3A>C）。该变异在包含46例患病个体与294例对照个体的更大规模斗牛㹴/迷你斗牛㹴联合队列中展现出完美的关联性。该变异在来自62个其他犬品种的462份遗传多样性丰富的对照犬基因组中均未出现。对一只患病犬与一只对照犬的皮肤RNA进行逆转录聚合酶链反应（RT-PCR）分析后发现，患LAD的犬的MKLN1转录本存在第4外显子跳跃现象，这会导致MKLN1的阅读框架发生移码突变。MKLN1基因编码广泛表达的细胞内蛋白muskelin 1，目前研究认为该蛋白在细胞黏附、细胞形态维持、铺展以及细胞内运输等过程中具备多种功能。尽管目前LAD的发病机制仍不明确，但本研究的数据可为斗牛㹴与迷你斗牛㹴的基因检测提供支撑，从而避免意外繁育出患LAD的犬只。本研究可为进一步阐明muskelin 1在体内的难以捉摸的生理功能提供全新的切入点。