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[Myotonic dystrophy: DNA instability in monozygotic twins]
L Redondo1, M A Polo, F Rodríguez
1Unidad de Neurología, Hosptial de Llerena, Badajoz, España. lredondov@meditex.es
Revista De Neurologia
|June 11, 1999
Summary
Myotonic dystrophy, a genetic disorder, involves CTG triplet expansion. In identical twins, this expansion occurred post-fertilization, not from paternal gametes, highlighting DNA instability.
Area of Science:
- Genetics
- Molecular Biology
Background:
- Myotonic dystrophy is an autosomal dominant disorder caused by CTG triplet expansion on chromosome 19q.
- This genetic condition exhibits variable expression and is linked to myotonia.
Observation:
- An unusual case involving monozygotic twin sisters with myotonic dystrophy was studied.
- CTG triplet expansion was analyzed in the lymphocytes of the twins and their family members, including the father's sperm.
Findings:
- The twin sisters displayed significant CTG triplet expansion (300-1,400 repeats) in their lymphocyte DNA.
- The father's lymphocyte and sperm DNA showed a smaller expansion (75 repeats), indicating paternal transmission with anticipation.
Implications:
- The study suggests CTG expansion in this case is not due to pre-existing paternal gamete expansion.
- Findings point to post-zygotic DNA instability during cellular mitosis as the mechanism for CTG expansion in myotonic dystrophy.