Abstract：
BACKGROUND: Epidermolytic palmoplantar keratoderma (EPPK) is characterized by diffuse hyperkeratosis affecting palms and soles with suprabasal epidermolysis or vacuolar degeneration histopathologically. The disorder is caused by heterozygous mutations in KRT9 or KRT1. Dominant-negative mutations in KRT1 could also result in epidermolytic ichthyosis with EPPK, a more severe entity affecting the entire body.
OBJECTIVE: To investigate the genetic basis and pathogenesis of two unrelated patients with EPPK and knuckle pads, both of whom were born to consanguineous parents of Chinese origin.
METHODS: Next-generation sequencing was applied to the two patients using genomic DNA extracted from peripheral blood. Quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR), immunofluorescence (IF) staining and Western blot (WB) were employed to evaluate mRNA and protein expression level. Ultrastructural changes of skin lesion were analysed using transmission electron microscopy.
RESULTS: Two novel homozygous mutations, c.457C>T (p.Gln153*) and c.33C>G (p.Tyr11*) in KRT1, were identified in patients 1 and 2 respectively. The nonsense mutations were predicted to result in nonsense-mediated mRNA decay and absence of keratin 1, which was confirmed in the skin lesions from patient 1. Upregulated keratin 2 was detected both in the affected and unaffected skin samples from patient 1, while the protein abundance and distribution pattern of keratin 10 remained unchanged. An aberrant and clumped staining pattern of keratin 9 was noted in the palmar skin of patient 1.
CONCLUSIONS: Homozygous \'knockout\' mutations in KRT1 resulted in EPPK with knuckle pads rather than epidermolytic ichthyosis. We speculated that sparing of non-acral skin might be due to compensatory effect of keratin 2 upregulation by forming heterodimer with keratin 10.
OBJECTIVE: To investigate the genetic basis and pathogenesis of two unrelated patients with EPPK and knuckle pads, both of whom were born to consanguineous parents of Chinese origin.
METHODS: Next-generation sequencing was applied to the two patients using genomic DNA extracted from peripheral blood. Quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR), immunofluorescence (IF) staining and Western blot (WB) were employed to evaluate mRNA and protein expression level. Ultrastructural changes of skin lesion were analysed using transmission electron microscopy.
RESULTS: Two novel homozygous mutations, c.457C>T (p.Gln153*) and c.33C>G (p.Tyr11*) in KRT1, were identified in patients 1 and 2 respectively. The nonsense mutations were predicted to result in nonsense-mediated mRNA decay and absence of keratin 1, which was confirmed in the skin lesions from patient 1. Upregulated keratin 2 was detected both in the affected and unaffected skin samples from patient 1, while the protein abundance and distribution pattern of keratin 10 remained unchanged. An aberrant and clumped staining pattern of keratin 9 was noted in the palmar skin of patient 1.
CONCLUSIONS: Homozygous \'knockout\' mutations in KRT1 resulted in EPPK with knuckle pads rather than epidermolytic ichthyosis. We speculated that sparing of non-acral skin might be due to compensatory effect of keratin 2 upregulation by forming heterodimer with keratin 10.
摘要：
背景：表皮松解性掌底角化病（EPPK）的特征是弥漫性角化过度，影响手掌和脚底，在组织病理学上伴有鼻上表皮松解或空泡变性。该疾病是由KRT9或KRT1中的杂合突变引起的。KRT1中的显性阴性突变也可能导致EPPK的表皮性鱼鳞病，影响整个身体的更严重的实体。
目的：探讨2例EPPK与关节垫无关患者的遗传基础和发病机制，两人都出生在中国血统的近亲。
方法：使用从外周血中提取的基因组DNA对两名患者进行下一代测序。定量逆转录酶聚合酶链反应（qRT-PCR），免疫荧光（IF）染色和Westernblot（WB）用于评估mRNA和蛋白质表达水平。使用透射电子显微镜分析皮肤病变的超微结构变化。
结果：两个新的纯合突变，c.457C>T（p。Gln153*）和c.33C>G（p。KRT1中的Tyr11*）分别在患者1和2中鉴定。预测无义突变会导致无义介导的mRNA衰减和角蛋白1的缺失，这在患者1的皮肤病变中得到了证实。在来自患者1的受影响和未受影响的皮肤样品中均检测到上调的角蛋白2,而角蛋白10的蛋白质丰度和分布模式保持不变。在患者1的手掌皮肤中注意到角蛋白9的异常和结块染色模式。
结论：KRT1中的纯合子“敲除”突变导致带有关节垫的EPPK而不是表皮性鱼鳞病。我们推测，保留非肢皮肤可能是由于角蛋白2通过与角蛋白10形成异二聚体而上调的补偿作用。
目的：探讨2例EPPK与关节垫无关患者的遗传基础和发病机制，两人都出生在中国血统的近亲。
方法：使用从外周血中提取的基因组DNA对两名患者进行下一代测序。定量逆转录酶聚合酶链反应（qRT-PCR），免疫荧光（IF）染色和Westernblot（WB）用于评估mRNA和蛋白质表达水平。使用透射电子显微镜分析皮肤病变的超微结构变化。
结果：两个新的纯合突变，c.457C>T（p。Gln153*）和c.33C>G（p。KRT1中的Tyr11*）分别在患者1和2中鉴定。预测无义突变会导致无义介导的mRNA衰减和角蛋白1的缺失，这在患者1的皮肤病变中得到了证实。在来自患者1的受影响和未受影响的皮肤样品中均检测到上调的角蛋白2,而角蛋白10的蛋白质丰度和分布模式保持不变。在患者1的手掌皮肤中注意到角蛋白9的异常和结块染色模式。
结论：KRT1中的纯合子“敲除”突变导致带有关节垫的EPPK而不是表皮性鱼鳞病。我们推测，保留非肢皮肤可能是由于角蛋白2通过与角蛋白10形成异二聚体而上调的补偿作用。
