Muscular dystrophies are group of inherited progressive muscular disorders,which are caused by mutations in the genes encoding proteins required for normal muscle growth and function .
Muscles can be affected by a variety of causes, genetic and acquired. Over the past few years, the fields of genetics and immunocytochemistry have expanded exponentially and this had led to a wealth of understanding of the inherited myopathies. The pathophysiological mechanisms of the disease processes are being elucidated at the molecular level and considering the rapidity of such developments, corrective therapy for these disorders appears to be a possibility.
A varied group of inherited, progressive degenerations of muscle, each with unique features.
X-linked recessive mutation of the dystrophin gene that affects males almost exclusively. Progressive weakness in hip and shoulder girdle muscles beginning by age 5; by age 12, the majority are nonambulatory. Survival beyond age 25 is rare. Patients usually become wheelchair-bound by 12 years and die in their late teens to early twenties. DMD is caused by mutations in the DMD gene, one of the largest known genes in humans, spanning 2.3 megabases and accounting for 0.1% of the total human genome.
The precise mechanism of how dystrophin deficiency leads to degeneration of muscle fibers remains unclear. Absence of dystrophin at the plasma membrane leads to delocalisation of dystrophin-associated proteins from the membrane, disruption of the cytoskeleton with resultant membrane instability and increased susceptibility to mechanical stress. In addition, altered membrane permeability and abnormal calcium homeostasis are thought to play a role, with increased cytosolic calcium concentration leading to activation of proteases such as calpains. The absence of nitric oxide synthase, delocalized from the subsarcolemmal membrane, may contribute to damage, but is not thought to directly cause dystrophic features such as - Motor delay or abnormal gait are the most frequent presenting complaint. repeated falls and weakness while climbing stairs and getting up from ground , Fatigue , Gowers maneuver seen in children , Hypertrophy of calf muscle.
Associated problems include tendon and muscle.contractures, progressive kyphoscoliosis, impaired pulmonary function, cardiomyopathy, and intellectual impairment.
Palpable enlargement and firmness of some muscles.
Genes contain codes, or recipes, for proteins, which are important biological components in all forms of life. BMD occurs when the dystrophin protein that's made from a particular gene on the X chromosome is only partially functional.
The dystrophin protein keeps the muscle cell membrane from breaking or tearing when our muscles contract and relax. Because it connects the center of the muscle cell to the periphery, the dystrophin protein is extremely long. One end is specialized for linking to the muscle interior, and the other end for linking to a variety of proteins at the cell membrane. The long middle section, called the rod domain, is taken up by a series of repeating units called spectrin repeats.
Some features are - pattern of muscle loss in BMD usually begins with the hips and pelvic area, the thighs, and the shoulders. To compensate for weakening muscles, a person with BMD may walk with a waddling gait, walk on his toes, or stick out his abdomen. Because muscular dystrophy doesn’t affect nerves directly, touch and other senses remain normal.
Cardiomyopathy is there due to wasting of muscle tissues of the heart.
life expectancy in BMD – survival age is upto 30 years.
Laboratory findings include massive elevations (20–100 × normal) of serum CK, a myopathic pattern on EMG testing, and evidence of groups of necrotic muscle fibers with regeneration, phagocytosis, and fatty replacement of muscle on biopsy.
Diagnosis is established by determination of dystrophin deficiency in muscle tissue or mutation analysis on peripheral blood leukocytes.
Ck level to be checked
Genetic and prenatal test is helpful in prior screening.
Type 1 is an autosomal dominant disorder with genetic anticipation. Weakness typically becomes obvious in the second to third decade and initially involves the muscles of the face, neck, and distal extremities.
This results in a distinctive facial appearance (“hatchet face”) characterized by ptosis, temporal wasting, drooping of the lower lip, and sagging of the jaw.
Myotonia manifests as a peculiar inability to relax muscles rapidly following a strong exertion (e.g., after tight hand grip) usually by the age of 5, as well as by sustained contraction of muscles following percussion (e.g., of tongue or thenar eminence).
Associated problems can include frontal baldness, posterior subcapsular cataracts, gonadal atrophy, respiratory and cardiac problems, endocrine abnormalities, intellectual impairment, and hypersomnia.
Cardiac disturbances, including complete heart block, may be life-threatening. Respiratory function should be carefully followed, as chronic hypoxia may lead to cor pulmonale.
normal or mildly elevated CK, characteristic myotonia and myopathic features on EMG, and a typical pattern of muscle fiber injury on biopsy, including selective type I fiber atrophy in 50% of cases. Pts with myotonic dystrophy type 1 have an unstable region of DNA with an increased number of trinucleotide CTG repeats on chromosome 19q13.3 in a protein kinase gene. Genetic testing for early detection and prenatal diagnosis is possible.
An autosomal dominant, slowly progressive disorder with onset in childhood or young adulthood. Weakness involves facial (usually the initial manifestation), shoulder girdle, and proximal arm muscles and can result in atrophy of biceps, triceps, and scapular winging. Facial weakness results in inability to smile, whistle, or fully close the eyes with loss of facial expressivity. Foot drop and leg weakness may cause falls and progressive difficulty with ambulation. Laboratory studies reveal normal or slightly elevated CK and usually myopathic features on EMG and muscle biopsy. Pts have deletions at chromosome 4q35. Genetic testing is available for carrier detection and prenatal diagnosis.
Onset in the fourth to sixth decade of ptosis, limitation of extraocular movements, and facial and cricopharyngeal weakness. One of several disorders characterized by progressive external ophthalmoplegia. Dysphagia may be life-threatening. Most pts are of French-Canadian or Spanish-American descent. Mutation in a poly-RNA binding protein responsible.
Numbness. Paralysis of single parts. Dull, tearing pain in hands and arms. Heaviness and weakness. Unsteadiness of muscles of forearm and hand. Numbness; loss of sensation in hands. Weak ankles. Cannot walk without suffering. Slow in learning to walk. Unsteady walking and easily falling. Restless legs at night.
Cannot raise or lift anything with the hand. Extension is difficult. Pains in muscles of thighs; come in paroxysms. Cramps in calves. Feet swollen. Pain in atrophied limbs alternates with colic. Loss of patellar reflex. Hands and feet cold.
Muscular weakness without impairing sensation and consciousness. Paralysis of respiratory muscles. Reflex action diminished. Catalepsy. Nervous debility. Trismus. Glycosuria with motor paralysis.
Tremulous, tottering gait. Knees knock against each other when walking. Cannot extend or cross legs when sitting. Myelitis, with marked spastic symptoms. Gluteal muscles and lower limbs emaciated. Legs blue; swollen, if hanging down. Stiffness and lameness of ankles and knees, toe do not leave the floor, heels do not touch floor, Muscles of calves very tense. Patient sits bent forward, straightens with difficulty.
Tearing in shoulders as if dislocated. Right shoulder painful, cannot raise it (Sang). Whole body feels tired and painful, especially legs and feet. Sense of numbness; nerve prostration.
Weakness from a short walk, with excessive heaviness. Heaviness of arms and legs on exertion, legs weak and heavy all the time.
Weakness of limbs on ascending stairs. Numbness and crawling in legs with trembling and pricking as from needles. Twitching on back of hip at 9 p.m. Hips and legs heavy all day. Knees weak.
Backs and legs give out. Uneasiness heaviness, and tearing in limbs and jerking. Limbs sensitive to pressure. Paralysis of old people. Limbs go to sleep easily.
Loss of power of muscular control. Cramp in muscles of forearm. Professional neuroses. Writer’s cramp. Excessive trembling and weakness of all limbs. Fatigue after slight exercise.