Uchino Y, Fukushige T, Yotsumoto S, Hashiguchi T, Taguchi H, Suzuki N, Konohana I, Kanzaki T
Department of Dermatology, Kagoshima University Faculty of Medicine, 8-35-1 Sakuragaoka, Kagoshima 890-8520, Japan.
Br J Dermatol. 2003 Jul;149(1):23-9. doi: 10.1046/j.1365-2133.2003.05365.x.
There are seven well-known lysosomal storage diseases that produce angiokeratoma corporis diffusum clinically. beta-Mannosidosis (MANB1; OMIM248510), first reported in humans in 1986, is a rare hereditary lysosomal storage disease caused by a deficiency of the enzyme beta-mannosidase. Since then, 13 cases of beta-mannosidase deficiency in ten families have been described. A human beta-mannosidase mutation has been reported only by Alkhayat et al. in 1998.
To clarify its pathogenesis we did electron microscopic, biochemical and molecular biological investigations of a Japanese patient with beta-mannosidosis.
Ultrastructural analyses, enzyme assays, cell culture and mRNA and genomic DNA were sequenced to find mutations in the beta-mannosidase gene.
Electron microscopy of skin biopsy specimens from the patient showed cytoplasmic vacuolation of lysosomes in blood and lymph vessels, endothelial cells, fibroblasts, secretory portions of eccrine sweat glands, neural cells and basal keratinocytes in the epidermis. This vacuolation was also observed in cultured keratinocytes and fibroblasts. Assays of seven enzyme activities in plasma and cultured skin fibroblasts showed a marked decrease of beta-mannosidase activity. Sequencing the beta-mannosidase cDNA revealed a four-base (ATAA) insertion between exons 7 and 8, resulting in a frameshift at codon 321 and termination at codon 325. Analysis of the patient's genomic DNA revealed a novel homozygous A(+1)-->G splice site mutation in intron 7.
To our knowledge, this is the first case of beta-mannosidosis reported in Japan and the second report in which a gene mutation is identified. The biological importance of beta-mannose moieties in glycoproteins in basal keratinocytes is suggested.
临床上有七种著名的溶酶体贮积病可导致全身性弥漫性血管角质瘤。β-甘露糖苷酶缺乏症（MANB1；OMIM248510）于1986年首次在人类中报道，是一种由β-甘露糖苷酶缺乏引起的罕见遗传性溶酶体贮积病。从那时起，已描述了十个家族中的13例β-甘露糖苷酶缺乏症病例。1998年，Alkhayat等人仅报道了1例人类β-甘露糖苷酶突变。
为阐明其发病机制，我们对一名日本β-甘露糖苷酶缺乏症患者进行了电子显微镜、生化和分子生物学研究。
进行超微结构分析、酶活性测定、细胞培养，并对β-甘露糖苷酶基因进行mRNA和基因组DNA测序以寻找突变。
对该患者皮肤活检标本进行电子显微镜检查发现，血液和淋巴管、内皮细胞、成纤维细胞、外分泌汗腺分泌部、神经细胞以及表皮基底角质形成细胞中的溶酶体出现细胞质空泡化。在培养的角质形成细胞和成纤维细胞中也观察到了这种空泡化。对血浆和培养的皮肤成纤维细胞中的七种酶活性进行测定，结果显示β-甘露糖苷酶活性显著降低。对β-甘露糖苷酶cDNA进行测序发现，外显子7和8之间有一个四碱基（ATAA）插入，导致密码子321处发生移码，并在密码子325处终止。对患者的基因组DNA进行分析发现，内含子7中有一个新的纯合A(+1)-->G剪接位点突变。
据我们所知，这是日本报道的首例β-甘露糖苷酶缺乏症病例，也是第二例鉴定出基因突变的报道。提示了β-甘露糖部分在基底角质形成细胞糖蛋白中的生物学重要性。
