Prenatal diagnosis of spinocerebellar ataxia type 3/Machado-Joseph disease in China's Mainland A case report

Spinocerebellar ataxia type 3/Machado-Joseph disease （SCA3/MJD） is a progressive, currently untreatable and ultimately fatal ataxic disorder that belongs to the group of neurological disorders known as CAG-repeat or polyglutamine diseases. Here, we present the first prenatal diagnosis of SCA3/MJD in China's Mainland in a woman who was known to carry an expanded CAG-trinucleotide repeat in the MJD1 gene. After evaluating motivation and psychological tolerance of the couple, amniocentesis was performed after 14 weeks of gestation. Polymerase chain reactions followed by T-vector cloning and direct sequencing were employed to evaluate the CAG-repeat number of the fetal MJD1 gene. We identified a truncated CAG expansion of 78 repeats in the MJD1 gene of the fetus compared with 81 repeats in his mother.

Emerging Concepts of Pathogenesis and Comprehensive Therapeutic Strategies for Spinocerebellar Ataxia Type 3

Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph Disease (MJD), is an autosomal dominant neurodegenerative disorder that predominantly involves the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems. SCA3 presents strong phenotypic heterogeneity and its causative mutation of SCA3 consists of an expansion of a CAG tract in exon 10 of the ATXN3 gene, situated at 14q32.1. The ATXN3 gene is ubiquitously expressed in neuronal and non-neuronal tissues, and also participates in cellular protein quality control pathways. Mutated ATXN3 alleles present about 45 to 87CAG repeats, which result in an expanded polyglutamine tract in ataxin-3. After mutation, the polyQ tract reaches the pathological threshold (about 50 glutamine residues);the protein is considered that it might gain a neurotoxic function through some unclear mechanisms. We reviewed the literature on the pathogenesis and therapeutic strategies of spinocerebellar ataxia type 3 patients. Conversion of the expanded protein is possible by enhancing protein refolding and degradation or preventing proteolytic cleavage and prevents the protein to reach the site of toxicity by altering its ability to translocate between the nucleus and cytoplasm. Proteasomal degradation and enhancing autophagic aggregate clearance are currently proposed remarkable therapy. In spite of extensive research, the molecular mechanisms of cellular toxicity resulting from mutant ataxin-3 remain no preventive treatment is currently available. These therapeutic strategies might be able to improve sign symptoms of SCA3 as well as slow the disease progression.

脊髓小脑共济失调3型的产前诊断方法研究

目的 探讨基于羊水细胞培养和毛细管电泳片段分析技术的脊髓小脑共济失调3型（SCA3/MJD）的产前诊断方法。方法 对1例孕20周的确诊SCA3/MJD患者及8名孕16~19周的高龄孕妇进行羊膜穿刺术并抽取羊水细胞培养。采用毛细管电泳片段分析技术对MJD1基因内（CAG）n重复序列动态突变进行检测。结果 SCA3/MJD患者胎儿MJD1基因（CAG）n次数为22/78次,胎儿携带其母亲的异常等位基因,诊断为SCA3/MJD。8例高龄孕妇胎儿MJD1基因（CAG）n重复次数13~26次,均在正常范围内。结论羊水细胞培养并毛细管电泳片段分析技术简便,准确,可作为SCA3/MJD产前诊断的可靠方法进一步推广。