Redondo L, Polo M A, Rodríguez F, Ramírez P, Aguilar J, Lucas M, Molano J
Unidad de Neurología, Hosptial de Llerena, Badajoz, España.
Rev Neurol. 1999;28(7):711-3.
Myotonic dystrophy is an autosomal dominant hereditary disorder with variable expression, associated with expansion of the CTG triplet on the gene which codifies myotonia situated on chromosome 19q. We present an unusual case of myotonic dystrophy in a pair of monozygotic twin sisters, determination of CTG expansion in lymphocytes of members of their family and in their father's spermatozoids.
The patients presented the phenomenon of anticipation of paternal transmission with an expansion of triplet CTG of lymphocyte DNA in a range of 300-1,400 identical repetitions in both. DNA of the paternal lymphocytes and spermatozoids showed a similar expansion of 75 repetitions.
CTG expansion is not due to previous expansion of DNA in the paternal gametes but to instability of DNA in the cellular mitoses following formation of the zygote.
强直性肌营养不良是一种常染色体显性遗传性疾病，表现多样，与位于19号染色体上编码肌强直的基因中CTG三联体的扩增有关。我们报告了一对单卵双胞胎姐妹患强直性肌营养不良的罕见病例，对其家庭成员淋巴细胞及父亲精子中的CTG扩增情况进行了测定。
患者出现父系遗传早现现象，两人淋巴细胞DNA中的三联体CTG扩增范围为300 - 1400个相同重复序列。父亲淋巴细胞和精子的DNA显示出75个重复序列的类似扩增。
CTG扩增并非由于父本配子中DNA先前的扩增，而是由于受精卵形成后细胞有丝分裂过程中DNA的不稳定性。
