Table 1:
Types of muscular dystrophies, their origin and phenotype
| Type | Gene associated | Mutation | Inheritance pattern | Age of onset | Muscles affected | Phenotype |
|---|---|---|---|---|---|---|
| Duchenne muscular dystrophy (DMD) | DMD | Loss of function | X-linked (recessive) | 3–5 years | Several muscles of the body and cardiac muscle | Progressive disease, which is fatal due to severe respiratory failure around 20–30 years of age. Patients are wheel chair bound in their early teenage |
| Becker muscular dystrophy (BMD) | DMD | Partial loss of function | X-linked (recessive) | Late childhood | Several muscles of the body and cardiac muscle | Milder than DMD but patients may die after forties if there are respiratory issues |
| Facioscapulo humeral muscular dystrophy (FSHD1 and 2) | DUX4 (type 1 and 2) SMCHD1 (type 2) | Contraction of DNA repeats in chromosome 4 and mutations in SMCHD1 | Autosomal dominant (type 1) Digenic (type 2) | Variable but mostly in 20s | Muscles of the face, shoulder, upper arm and lower legs | Rarely fatal but severely affects the quality of life |
| Myotonic dystrophy (DM1 and DM2) | DMPK (type 1) CNBP (type 2) | Expansion of DNA repeats | Autosomal dominant | Variable for DM1 (birth to 40 years), adult onset for DM2 | Muscles of face, shoulder, lower arms and legs (type 1), Muscles of the neck, shoulders, elbows and hips (type 2) | Difficulty in muscle relaxation and muscle weakness. Congenital onset can be fatal if there are respiratory issues |
| Limb girdle muscular dystrophy (LGMD1 and LGMD2) | MYOT (LGMD1A), (LMNA) LGMD1B, CAV3 (LGMD1C), DNAJB6, (LGMD1D), DES (LGMD1E), CAPN3 (LGMD2A), DYSF (LGMD 2B), SGCG (LGMD2C), SGCA (LGMD2D), SGCB (LGMD2E), SGCD (LGMD2F), TCAP (LGMD2G), TRIM32 (LGMD2H), FKRP (LGMD2I), TTN (LGMD2J), | Usually loss of function mutations | Autosomal dominant (Type 1) or recessive (Type 2) | Variable | Typically muscles around the should and pelvic girdles but some types can affect cardiac muscle | Phenotype is variable. Affects the quality of life. Rarely fatal if there is weakness of cardiac and respiratory muscles |
| Pompe disease | GAA | Usually loss of function mutations | Autosomal recessive | Variable, from birth to adulthood | Respiratory muscles, muscles of hip, upper arms, legs and shoulder | Phenotype is variable. Early onset forms can be fatal |