Risk factors for myotonic dystrophy type 1 and organic system involvement
| CF, congenital form only; CTG, cytosine–thymine–guanine; DHEA, dehydroepiandrosterone; HPA, hypothalamic–pituitary–adrenal |
| % = reported frequency in the literature. |
| Risk factors |
| Dominant autosomal disease |
| CTG expansion at 19q13.33 |
| Anticipation2 |
| Organic systems |
| Muscular |
| Variations in fibre size, atrophy of type 1 fibres |
| Ringed fibres, increased central nuclei, nuclear chains21 |
| Nervous |
| General and focal cerebral atrophy, progressive ventricular dilatation, white matter lesions22–25 |
| Reduced cortical glucose utilisation26 |
| Reduced blood flow in fronto-temporal regions bilaterally25–27 |
| Central motor control involved28 |
| Auricular |
| Bilateral high tone hearing loss29 |
| Ocular |
| Early cataracts (78–97%), frequent symmetrical ptosis2,30 |
| Retinopathy, blepharitis, corneal lesions2 |
| Digestive |
| Locking of the jaw, weakness of the palate and decreased chewing ability2,31 |
| Smooth muscle dysfunction affecting all parts of the GI tract32 |
| Slow oesophageal transit and gastric emptying33 |
| Small intestine and colonic dysmotility,33 colonic pseudo-obstruction |
| Bile acid malabsorption, high incidence of gall bladder stones33 |
| Anal sphincter weakness and myotonia34 |
| Respiratory |
| Alveolar hypoventilation, marked hypercapnia35 |
| Respiratory muscle weakness35 and myotonia36 |
| Restrictive respiratory disease (58%)35 |
| Central37 and obstructive sleep apnoea38 |
| Cardiovascular |
| Extensive involvement of cardiac conducting tissue with fatty infiltration, fibrosis and degenerative change39 |
| Abnormal ECG (65%)40–42 |
| AV conduction disturbances, heart block, atrial flutter and fibrillation39,43 |
| Ventricular tachy/brady-arrhythmias42 |
| Hypotension44 |
| Sudden death (8–30%)39,43,45 (2nd cause of death)45 |
| Endocrine |
| Hypogonadism, testicular atrophy (60–90%)2 |
| Hyperinsulinaemia, diabetes2 |
| HPA axis disturbance, abnormal diurnal rhythm of cortisol46 |
| Growth hormone secretion disturbance,47 hyperleptinaemia48 |
| Increased interleukin 6 and tumour necrosis factor α49 |
| Decreased DHEA and DHEA sulphate50 |
| Urinary |
| Urgency, frequency and stress incontinence51 |
| Reproductive |
| Uterus; incoordinate contraction in labour and in vivo2 |
| Skeletal |
| Talipes (CF)2 |
| Cutaneous |
| Premature balding2 |