Health

Duchenne’s muscular dystrophy (DMD) is perhaps one of the most well-known dystrophies. DMD affects 1 in 3,500 male births of all races; girls are usually not affected but may pass this gene on to their children. In this disease, a specific muscle membrane protein called dystrophin is virtually absent, secondary to a genetic alteration. Because the gene that codes for dystrophin is about 10 times longer than the next largest known gene (about 2.5 million base pairs of DNA), it is quite easy to imagine how many ways this gene could be altered. As a result, most of these genetic changes are new changes (spontaneous mutations), not passed along from the mother (even though transmission is X-linked).

Boys with DMD typically walk later than their peers and usually walk on their toes. Parents usually notice that their son has difficulty climbing stairs, or getting up from the floor, falls frequently, or “walks funny.” Boys usually need to climb up on their own selves using Gower’s Maneuver to rise up off the floor; big calves are also commonly seen. By age 12, most boys use a wheelchair to get around. Besides the skeletal muscles, muscles of the lung and heart are also affected. There is also evidence that boys with DMD may have a higher incidence of learning deficits or cognitive (thinking) deficits compared to age-matched peers, but IQ typically remains stable over the course of the disease.

As the disease progresses, boys find breathing harder and harder; some choose to use positive pressure or mechanical ventilation. Pulmonary function tests (breathing tests) are followed regularly to monitor disease progression. Cardiac medications may become necessary, especially in boys over 13 years old, secondary to progressive cardiomyopathy (enlarged heart) and associated conduction defects. Regular follow-up with a cardiologist for an electrocardiogram (study of the heart rhythm) and other tests is necessary. Most boys do not survive past their 20s unless they choose mechanical or positive pressure ventilation.

Scoliosis secondary to trunk muscle weakness is another complication in DMD; spinal surgery is often recommended to maintain adequate lung function and positioning. Joint contractures (tight joints) often develop in boys over age 13 years. Some boys with DMD may experience serious problems with general anesthesia, especially halothane and succinylcholine, and this potential complication must be considered in all boys when planning surgery.

Getting enough nutrition is also an issue late in the course of DMD. At this stage, boys have difficulty feeding themselves secondary to the extreme arm muscle weakness; they also have problems with upper gastrointestinal (stomach) function and swallowing. Nutritional supplementation is often recommended; some studies note a small reduction in muscle protein breakdown with branched chain ketoacid supplementation (specific amino acid diet).

Becker’s muscular dystrophy (BMD) is a milder form of DMD, as some amount of the muscle membrane protein, dystrophin, is present. Problems are similar to DMD, but they occur at a slower pace. Boys often walk into their teens and live well past their 20s into middle age and some up to age 60. Heart problems are also common in BMD; some rarer cases include cardiomyopathy (enlarged heart) without skeletal muscle weakness. Becker’s is thought to affect 1 in 50,000 live male births.

Congenital muscular dystrophy affects both boys and girls but is rarer. It is caused by a deficiency in a muscle protein called merosin. Depending on the severity of this deficiency, low tone (floppiness) and weakness may be noticeable at birth, infancy, or early childhood. In the most affected babies, breathing, swallowing, and sucking may all be impaired. Stiff joints leading to an inability to move these joints (joint contractures) may develop if limbs aren’t regularly moved. Scoliosis (back curvature) may also develop over time. Some less affected babies may gain developmental milestones and even achieve the ability to walk with assistive devices.

Myotonic muscular dystrophy is quite common, affecting 1 in 8,000 persons. Myotonia means “difficulty relaxing;” MMD is characterized by an inability to relax muscles at will. For example, persons with MMD may not be able to open their hands up quickly after making a tight fist; often handshakes are prolonged, especially in cold weather. There are two forms of this disease. Type 1 is the most common form; Type 2 is found in less than 5% of those with MMD and usually affects those of German ancestry. People with Type 1 MMD may have characteristic balding, narrowed forehead (temporal wasting), and decreased facial expression in their lower face, secondary to a loose or slack jaw caused by facial muscle weakness. This type of MMD gets worse in each generation, but unpredictably. A mother who is minimally affected may have a newborn that is profoundly affected with difficulty breathing, nursing, or crying. These babies have a characteristic “inverted V” type of upper lip.

MMD is often called a systemic illness because it can affect many organ systems. Cardiac complications occur in one half to two thirds of affected persons, including cardiomegaly (enlarged heart) and conduction defects. Pacemakers may be necessary in some cases. Cataracts are common in 90% of those with Type 1 MMD. Gastrointestinal problems, including constipation, slow swallowing, and gallbladder problems may occur. Infertility is common in both sexes. There may be increased risks with anesthesia, barbiturates, and other medications that may affect the respiratory drive (body’s automated breathing system). Mental slowness may be a part of MMD, especially in more affected individuals with this disease.

Limb girdle dystrophies (LGD) are muscle diseases that cause weakness in the hip or shoulder area. From genetic testing, many different types of limb girdle dystrophies that affect specific muscle proteins have been described. Some of these protein deficiencies include calpain-3 as well as deficiencies in alpha, beta, gamma, or delta sarcoglycan. Weakness most commonly begins when the person is 10-30 years old. People with limb girdle dystrophies usually need braces or assistive devices to continue walking as the disease progresses. Cardiomyopathy (heart muscle disease) is also a concern in these LGD. Intellect is normal.

Facioscapulohumeral muscular dystrophy (FSH) is a slowly progressive dystrophy that involves mainly the muscles of the face and shoulder. It’s been difficult to determine the actual number of persons with FSH because there are many mild undiagnosed cases, and there can be a spectrum of mild to severe in the same family; estimates are 10-20 persons per million. Facial weakness leads to difficulty closing one’s eyes, whistling, pursing one’s lips, drinking through a straw, or even smiling. The scapulas (wing bones on the back) often stick out, and one shoulder may be smaller than the other. This often becomes noticeable in adolescence or early adulthood. Hip muscles and ankles may become weaker later on as the disease slowly progresses. A rare infant onset FSH, Coat’s syndrome, may have associated progressive vision changes as well as hearing deficits. Hearing problems may occur less often in non-infant onset FSH. Dry eyes due to weak eye closure, and difficulty with eating, drinking due to mouth weakness may require plastic surgery intervention. There are no associated cardiac abnormalities. Lifespan is usually normal.

Emery-Dreifuss muscular dystrophy is a rare, slowly progressive dystrophy that may appear in boyhood, adolescence, or early adulthood dependent on severity. It is caused by a deficiency in the muscle protein emerin. Elbow contractures (fixed joints) are a hallmark of this disease; boys notice that they are unable to fully extend their arm out straight. Heel cords (Achilles tendon) may become tight early on, causing toe-walking. Extensor muscles of the cervical (neck) and thoracic (mid back) may also become tight, limiting neck flexion (i.e., putting chin to chest) and the ability to touch the toes. There is often a loss of muscle bulk in the upper arm (biceps) and calves. Cardiomyopathy (enlarged heart) and arrhythmias (abnormal heart electrical rhythms) are serious and may cause sudden death in early adulthood; providing a cardiac pacemaker may be life-saving. Survival is generally into middle age if a pacemaker is provided at the time of diagnosis.