Alkhayat A H, Kraemer S A, Leipprandt J R, Macek M, Kleijer W J, Friderici K H
Department of Pathology, Michigan State University, East Lansing, MI 48824, USA.
Hum Mol Genet. 1998 Jan;7(1):75-83. doi: 10.1093/hmg/7.1.75.
Human beta-mannosidosis is an autosomal recessive, lysosomal storage disease caused by a deficiency of the enzyme beta-mannosidase. Unlike the severe clinical manifestation of the disease in ruminants, in which it leads to neonatal death, the human disease phenotype is generally milder. In addition, the phenotypic manifestation among the reported cases of human beta-mannosidosis is variable, even among members of the same family. To understand the molecular basis of the human disease and the mechanisms for such clinical variability, we sequenced the entire coding region of the human beta-mannosidase gene using a combination of cDNA library screening, RT-PCR and 5' rapid amplification of cDNA ends (RACE). The composite cDNA is 3293 nt, consisting of an 87 nt 5'-untranslated region, 2640 nt coding region and 566 nt 3'-untranslated region. The gene was localized to human chromosome 4q22-25. Analysis of a multiple tissue northern blot demonstrated a single 3.7 kb transcript. Mutation analysis of a Czech gypsy family with two siblings differently affected with beta-mannosidosis demonstrated a homozygous A-->G transition 2 bp upstream of a splice acceptor site. The associated cryptic splice site activation and exon skipping caused by this mutation resulted in two abnormally spliced mutant mRNA species in both siblings.
人类β-甘露糖苷贮积症是一种常染色体隐性溶酶体贮积病，由β-甘露糖苷酶缺乏引起。与反刍动物中该疾病导致新生儿死亡的严重临床表现不同，人类疾病的表型通常较为温和。此外，在已报道的人类β-甘露糖苷贮积症病例中，即使在同一家族成员中，表型表现也存在差异。为了了解人类疾病的分子基础以及这种临床变异性的机制，我们结合cDNA文库筛选、逆转录聚合酶链反应（RT-PCR）和5' cDNA末端快速扩增（RACE）技术，对人类β-甘露糖苷酶基因的整个编码区进行了测序。合成的cDNA为3293个核苷酸，由一个87个核苷酸的5'非翻译区、2640个核苷酸的编码区和566个核苷酸的3'非翻译区组成。该基因定位于人类染色体4q22 - 25。对一个有两个患β-甘露糖苷贮积症程度不同的兄弟姐妹的捷克吉普赛家族进行的突变分析表明，在一个剪接受体位点上游2个碱基处存在纯合的A→G转换。这种突变导致的相关隐蔽剪接位点激活和外显子跳跃，在两个兄弟姐妹中产生了两种异常剪接的突变mRNA。
