When copying the mutated gene, DNA polymerase can basically lose track of which CAG it's on and accidentally add extra CAGs.

在复制突变基因时，DNA聚合酶基本上无法定位它所处的CAG位置，并由此意外添加了额外的CAG。

When copying the HTT gene, DNA polymerase can basically lose track of which CAG it's on and accidently add extra CAGs.

当HTT基因复制时，DNA聚合酶基本上无法识别校对CAG序列，意外地导致CAG序列重复。

Even repeats of 27-35 CAGs can expand occasionally; these are called " pre-mutation" alleles, since they don't cause the disease, but they're set-up for developing a mutation of 36 or more CAGs.

即使CAG序列重复在27-35次间，偶尔也会产生异常，这些被称为突变前等位基因，尽管不会引起疾病，但仍可能会发展为36次以上CAG序列重复的突变。