Letters to the editor
Trinucleotide repeat contraction: a pitfall in prenatal diagnosis of myotonic dystrophy
Jeanne Amiela, Valérie Raclina, Jean-Marie Jouannicb, Nicole Morichona, Hélène Hoffman-Radvanyic, Marc Dommerguesb, Josué Feingolda, Arnold Munnicha, Jean-Paul Bonnefonta da Département
de Génétique et Unité INSERM U-393, Hôpital Necker-Enfants
Malades, 149 rue de Sèvres, 75743 Paris cedex 15, France, b Maternité,
Hôpital Necker-Enfants Malades, Paris, France, c Service de Biochimie,
Hôpital Ambroise Paré, Boulogne, France, d Service
de Biochimie B, Hôpital Necker-Enfants Malades, Paris, France
Correspondence to: Dr Bonnefont, bonnefon@necker.fr
| The first 150 words of the full text of this article appear below. |
 |
Introduction |
|---|
EDITOR
Myotonic dystrophy (DM) is a common
autosomal dominant disorder characterised by myotonia, muscle weakness,
ECG abnormalities, cataracts, hypogonadism, and frontal balding in the
typical adult form (MIM 160900). The genetic defect consists of the
amplification of an unstable CTG trinucleotide repeat in the 3'
untranslated region of the dystrophia myotonica protein kinase gene
(DMPK), which maps to
19q13.3.1 2 Normal subjects have five to 37 repeat copies
while affected subjects have over 50 repeats.1 There is
some correlation between repeat length and clinical symptoms, especially with respect to the age at onset.3-6 In the
vast majority of cases, the number of repeats increases during
parent-offspring transmission of the mutant allele, thus providing some
molecular basis to the observation of anticipation (increased severity
of the disease in successive generations).7 8 However, a
decrease in repeat size is occasionally observed in the offspring,
mostly in the case of paternal transmission of
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