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APRIL 2022 InTouch | 15 Congenital myotonic dystrophy may also result in severe learning problems and sometimes an individual may be mentally retarded. Special education is often necessary because of these disabilities. What Causes Myotonic Dystrophy? All types of DM are autosomal dominant disorders. Humans have 46 chromosomes made up of genes. Each chromosome, which is a tightly coiled chain of DNA (deoxyribose nucleic acid) contains millions of chemicals called bases. The four bases are adenine, thymine, cytosine and guanine (A, T, C and G), which pair together in sets of three to form coded messages. These messages are instructions for producing proteins that make the body function. Many disorders are a result of a mutation to these bases. In all forms of DM, there is an abnormal expansion of different sequences of bases. In DM1 and Congenital Myotonic Dystrophy it is a result of an expanded repeat of the CTG sequence in the DMPK (dystrophica myotonica protein kinase) gene on chromosome 19. DM2 is a result of a expanded repeat of CCTG in the ZNF9 (zinc finger protein 9) on chromosome 3. Generally a greater expansion is related to earlier onset and faster progression of the disorder. How these mutations directly affect all the different systems of individuals is currently unknown, however researchers have hypothesized that the problem lies in RNA, which is a copied version of DNA for processing genes into proteins. When the expanded sequence in the DNA is copied, there is an over-accumulation of RNA which traps the information inside the center of the cell. This blocks several other types of RNA and disrupts the protein-manufacturing process for the genes which control several bodily processes. Diagnosis of Myotonic Dystrophy Diagnosis usually commences after the identification of key early symptoms of DM: • ‘Grip Test’ – affected individuals will not be able to open and close their hand rapidly and will have a characteristic grip • Blood Testing – elevated levels of creatine phosphokinase (CPK) are indicative of muscle problems • Electromyography (EMG) – observes the electrical activity of muscles and its consistency with activity typical of DM individuals • Muscle Biopsy – looks at an individual’s muscle cells for characteristic features of DM • DNA Testing – can identify the presence of the abnormal gene in the individual with DM Soon after a diagnosis of DM in the family, it is essential that genetic counselling is arranged, for one or both of two issues. The first is the probability of Mum or Dad having the disorder, and the second is whether testing for DM in pregnancy can be offered and with what degree of accuracy. Genetic counselling provides information about possible diagnostic tests, including prenatal testing. Genetic services in NZ are available and a referral can be made by the MDANZ. Management of Myotonic Dystrophy As there is currently no cure for DM, treatment focuses on the prevention and management of symptoms which, as explained above, differ from one individual to another, dependent on how severely he or she is affected. MYOTONIC DYSTROPHY (DM) This diagram shows the location of the genetic error which causes Myotonic Dystrophy. One copy of the gene with an error is enough to cause the condition. Type 1 is caused by an error in the DMPK gene on chromosome 19 and Type 2 is caused by an error in the CNBP gene on chromsome 3. DM TYPE 1 DM TYPE 2 DMPK gene 19q13 CNBP gene 3q13-q24 p p q q