Clinical features: An inherited muscular dystrophy characterised by progressive muscle weakness, difficulty relaxing clenched hands (myotonia), cataracts, ECG changes and hypogonadism and frontal balding in males. The condition is extremely variable and there is a well recognised severe congenital form of the disease. It is important that an anaesthetist knows that a patient has myotonic dystrophy to avoid potential complications associated with certain anaesthetics.
Incidence: Approximately 1 in 8,000.
Inheritance: :Autosomal dominant.
Gene: The commonest form of myotonic dystrophy is caused by a mutation in the dystrophia myotonica protein kinase gene (DMPK) on chromosome 19. The mutation is an amplified CTG triplet (trinucleotide) repeat and the severity of the condition varies with the number of repeats. In unaffected individuals there are between 5 and 30 repeat copies. Mildly affected individuals have from 50 to 80 repeats and children with the severe congenital form of the condition 2,000 or more copies. The CTG repeat number usually increases from one generation to the next (amplification), although very large amplifications occur only when the gene is transmitted through females. This explains why myotonic dystrophy increases in severity with successive generations (anticipation) and why babies with the severe congenital form of the condition are almost exclusively born to affected women.
Prenatal diagnosis: Yes, by DNA testing to determine whether the expanded repeat sequence is present. If a family is considering prenatal diagnosis, referral should be made to the local clinical genetics service prior to a pregnancy. This ensures family members are offered appropriate advice and investigations, to confirm whether or not prenatal diagnosis is possible.
Presymptomatic testing: Yes.
UK Support Group: Myotonic Dystrophy Support Group 175A Carlton Hill Carlton Nottingham NG4 1GZ Tel 0115 987 0080 (Helpline) Tel 0115 987 5869 (Office) Fax: 0115 987 6462 Web: www.mdsguk.org
If you would like to access specialist information on myotonic dystrophy please go to:- Genetests - Myotonic dystrophy
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