巨轴索神经病家系的临床和基因诊断研究

Clinical and Genetic Studies on Giant Axonal Neuropathy

目的通过2个巨轴索神经病(GAN)家系进行基因突变位点筛查,找到致病位点。方法采用盐析法提取GAN家系成员基因组DNA,采用PCR方法扩增GAN基因的编码外显子,纯化后直接测序。结果在1号先证者GAN基因上发现2个杂合错义突变。1.第2外显子核苷酸序列第224位T>A突变(c.224T>A),该错义突变引起编码的第75位氨基酸由亮氨酸(L)变为组氨酸(H)(L75H);先证者母亲是该突变的杂合携带者,具有正常表型,先证者父亲在该位点为正常基因型。2.第10外显子核苷酸序列第1634位G>A突变(c.1634G>A),该错义突变引起编码的第545位氨基酸从精氨酸(R)变为组氨酸(H)(R545H);先证者父亲是该突变的杂合携带者,具有正常表型,先证者母亲在该位点为正常基因型。这2个错义突变均能引起GAN基因编码氨基酸的改变,从而引起蛋白质结构和功能异常。2号先证者GAN基因未发现突变位点。结论在第1个家系中,c.224T>A和c.1634G>A错义突变导致先证者出现GAN的表型,其父母分别是2个突变的携带者,均具有正常表型。第2个家系可能存在其他遗传方式。

Objective To investigate 2 giant axonal neuropathy （GAN） families and detect the mutation of GAN gene in their family.Methods The encoding exons of GAN gene were amplified from genomic DNA of the probands and their parents by PCR and directly sequenced after getting purified.Results No.1 proband manifested typical neurological symptoms and pathological abnormalities.The case of the girl had 2 heterozygous missense mutations in GAN gene：1.c.224T〉A in exon 2,which results in the amino acid change of L75H;her mother was a heterozygote of this mutation and had normal phenotype,while her father had normal genotype in this site;2.c.1634G〉A in exon 10,her father was a heterozygote of this mutation and had normal phenotype,while her mother had normal genotype in this site.Both of the mutations cause amino acid changes in the gigaxonin protein.No mutation was detected in proband No.2.Conclusions In family 1,missense mutation of c.224TA and missense mutation of c.1634G〉A in GAN gene cause the phenotype of GAN in the proband.The girl′s parents are heterozygotes of the disease without symptoms.There may be other mode of inheritance in family 2.