Types of Muscular Dystrophies

Duchenne Muscular Dystrophy (DMD)

The symptoms and signs of DMD are typically seen in early childhood with toe-walking, difficulty rising from the floor, gait difficulties, and frequent falls.  The disease typically progresses to loss of ambulation by the second decade of life. DMD is an X-linked recessive disorder caused by mutations in the dystrophine gene (gene symbol DMD) and is thus present almost exclusively among males, though some female carriers may show signs of the disease.  DMD is accompanied by lung, heart, and bone complications that require ongoing monitoring and treatment. Recent advances include several FDA-approved therapies and numerous active clinical trials.

Becker Muscular Dystrophy (BMD)

BMD is caused by mutations in the gene DMD but has a milder course and typically a later age of onset. Some patients have significant weakness during the adolescent years while other affected adolescents remain virtually asymptomatic for prolonged periods of time.

As there is much overlap between DMD and BMD both genetically and clinically, MD STARnet studies them together as a combined category called DBMD.

Facioscapulohumeral Dystrophy (FSHD):

The muscle weakness in FSHD is seen in the face (facio), shoulder (scapulo), upper arms (humeral), abdomen and legs and often displays an asymmetrical pattern. Other manifestations include hearing impairment and pain.

The disease is slowly progressive and most people notice the weakness in their late teens or twenties. In a small percentage of individuals, weakness might be evident in early childhood. FSH is not considered life threatening and most people have a normal life span, though over the course of the disease significant impacts on quality of life occur.

Myotonic Dystrophy (DM):

DM is a complex, multi-organ system disease with variable symptoms and patterns of disease progression. The genetic mutation is a repeat expansion, with two subtypes recognized.  DM1 is caused by an expansion of a CTG motif in the DMPK gene and is associated with predominantly distal weakness.  Onset of DM1 can range from birth to middle adulthood.  DM2 is caused by an expansion of a CCTG motif in the ZNF9 gene and is associated with proximal weakness.  Onset of DM2 is typically during adulthood.  Aside from muscle weakness, DM1 and DM2 share the occurrence of cardiac complications, premature cataracts, white matter changes on brain MRI, mildly abnormal liver measures, and primary hypogonadism for males.  DM1 may also be complicated by sleep problems/somnolence, behavioral issues, intellectual disabilities, gastrointestinal dysmotility, increased cancer risks, insulin resistance, lipid/cholesterol derangements, and balding.  The somnolence is often a major problem that impacts school and social activities.

Limb-Girdle Muscular Dystrophy (LGMD):

LGMDs are a genetically diverse group of muscle diseases that share in common a pattern of progressive, proximal muscle weakness. Over 30 genes have been associated with various forms of LGMD.  The more severely affected individuals tend to have a clinical course that resembles DMD, whereas the less affected patients may be said to follow a course similar to that of BMD.  Cardiac and cognitive complications tend to be uncommon among many of the subtypes of LGMD.

Congenital Muscular Dystrophy (CMD):

There are three major subtypes of CMD which shape the clinical course of the disease: collagenopathy, merosinopathy, and dystroglycanopathy. By definition, onset is in the first two years of life. The muscles of the neck, upper arms, upper legs tend to be affected first. Broadly speaking, collagenopathy is the mildest subtype and is associated with no functional or structural brain complications.  Merosinopathy is classically associated with white matter changes on brain MRI but little to no functional brain dysfunction.  Dystroglycanopathy is often associated with significant brain malformations and structural eye abnormalities.

Emery-Dreifuss Muscular Dystrophy (EDMD):

EDMD is characterized by a triad of early contractures, cardiomyopathy, and muscle weakness. The classic genes associated with EDMD are EMD and LMNA, though several other less common genes have been described as well. EMD is on the X chromosome so EMD-associated cases affect primarily males, whereas LMNA-associated cases affect sexes equally. Symptoms and signs appear during childhood and the contractures typically limit movement of the elbow, neck, and/or ankle joints.

Oculopharyngeal Muscular Dystrophy (OPMD):

The onset of this disease is typically in the 5th or 6th decade. As the name implies, the disease affects mainly the eyes and the pharynx, with manifestations that include droopy eyelids and/or difficulty swallowing.  Weakness of the proximal arms and legs tends to progress slowly.

Distal Muscular Dystrophy (DD):

This is a rare form of muscular dystrophy with onset typically in adulthood. As suggested by the name, distal upper and lower extremities are preferentially affected.