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Metabolic Diseases of the Muscle

Each of the metabolic disorders of the muscle are caused by different genetic defects that impair the body's ability to process chemical reactions that occur within cells during normal functioning. Under normal conditions, fuel molecules broken down from the food, and then are broken down further inside of each cell before they can be used by the mitochondria of the cell to produce ATP. The metabolic diseases of the muscle results from problems that occur when certain fuel molecules are processed before they enter the mitochondria, or by the cell's inability to get fuel molecules into the mitochondria. ATP drives all muscle activity in the body, and when ATP levels are low, muscle weakness, pain or cramps may occur. Metabolic diseases that are diagnosed at infancy are most severe; however, those that begin in childhood or adulthood tend to be less severe, and changes in lifestyle or diet can help these mild forms.

Phosphorylase Deficiency (MPD or PYGM) (also known as McArdle's Disease)

Phosphorylase Deficiency (MPD) is an autosomal recessive muscle disease that interferes with the processing of carbohydrates to draw energy from food. More specifically, a genetic defect in the phosphorylase enzyme results in the cell's inability to breakdown glycogen. Patients are diagnosed anywhere from childhood to adulthood and suffer from symptoms including cramps, muscle pain, muscle weakness and exercise intolerance.

Acid Maltose Deficiency (AMD) (also known as Pompe's Disease)

Acid Maltose Deficiency (AMD) is caused by complete or partial deficiency of the lysosomal enzyme, alpha-glucoidase, the enzyme necessary for the breakdown and conversion of glycogen into glucose. Absence of alpha-glucosidase results in accumulation of a thick sticky substance in the lysosomes (sacs within the muscle cells). Eventually this leads to severe muscle degradation. AMD affects the heart, skeletal and respiratory muscles of the patient. This autosomal recessive disorder can be recognized in patients from infancy to adulthood. AMD is slowly progressive and less severe in childhood and adult-onset forms; the infantile form often leads to death by two years of age.

Phosphofrucokinase Deficiency (PFKM) (also known as Tarui's Disease)

Phosphofructokinase Deficiency (PFKM) is one of the group of muscle disease that interferes with the processing of carbohydrates to draw energy from food. The cause of PFKM is thought to be a result of a genetic defect in the phosphofructokinase enzyme, which affects the storage and breakdown of glucose. Onset is anywhere from childhood to adulthood and is inherited by the contribution of a defective gene from each parent (autosomal recessive). Symptoms for PFKM include exercise intolerance, pain, cramping and occasionally myoglobinuria (rust-colored urine indicting breakdown of muscle tissue).

Debrancher Enzyme Deficiency (DBD) (also known as Cori's or Forbes Disease)

Debrancher Enzyme Deficiency (DBD) is an autosomal recessive disorder caused by a genetic defect in the debrancher enzyme, which affects the breakdown of glycogen, the stored form of glucose(sugar). The progression of the disease is slow, except in the severe infantile form. Symptoms are generalized weakness and muscle wasting, enlarged liver in infancy, and episodes of low blood sugar.

Mitochondrial Myopathy (MITO)

Mitochondrial Myopathy (MITO) is a group of diseases affecting the mitochondria, small structures located outside of the nucleus in the cytoplasm that are responsible for energy production in cells. Mitochondrial Myopathy is a group comprised of Kearns-Sayre Syndrome, Leigh's syndrome, Mitochondrial DNA Depletion Syndrome (MDS), Mitochondrial Encephalomyopathy, Lactic Acidosis and Strokelike Episodes (MELAS), Myoclonus Epilespsy with Ragged Red Fibers (MERRF), Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE), Neuropathy, Ataxia and Retinitis Pigmentosa (NARP), and Progressive External Ophthalmoplegia (PEO). These disorders are caused by defects in genes that produce proteins that process food into energy inside cells. The affected protein determines which of the many mitochondrial diseases are present. The onset of most mitochondrial myopathies is before the age of 20 and they often begin with muscle weakness. During physical activity muscles may become easily fatigued or weak. Besides fatigue and muscle weakness, symptoms also include nausea, vomiting, headache, seizures, stroke-like episodes, droopy eyelids, blindness, deafness, heart failure and heart rhythm disturbances. Progression varies according to the specific disease as well as inheritance.

Carnitine Deficiency (CD)

Carnitine Deficiency (CD) is one of a group of muscle diseases that interferes with the processing of fats to draw energy from food. CD is caused by a defect in a gene for protein that brings carnitine into the cell. The slowly progressive disease is autosomal recessive, caused by the contribution of a defective gene from each parent. The onset of CD is usually at early childhood. Symptoms include cardiac disease, muscle weakness in the hips, shoulders and upper arms and legs. Neck and jaw muscles may also be weak.

Carnitine Palmityl Transferase Deficiency (CPT), Onset: Young adulthood.

Phosphoglycerate Kinase Deficiency (PGK)

Phosphoglycerate Kinase Deficiency (PGK) is an X-linked recessive muscle disease that interferes with the processing of carbohydrates to draw energy from food. PGK is caused by a genetic defect in the phosphoglycerate kinase enzyme, which affects the processing of carbohydrates for fuel. Diagnosis of PGK usually occurs anywhere from infancy to early adulthood. Muscle symptoms are slowly progressive and may include weakness, exercise intolerance, muscle cramping and episodes of myoglubinuria (rust-colored urine indicating the breakdown of muscle tissue). PGK also may cause anemia, enlargement of the spleen, mental retardation and epilepsy.

Phosphoglycerate Mutase Deficiency (PGAM or PGAMM), Onset: Early adulthood.

Lactate Dehydrogenase Deficiency (LDHA), Onset: early adulthood.

Myoadenylate Deaminase Deficiency (MAD),Onset: early adulthood to middle age.