Brody myopathy is a condition that affects the skeletal muscles, which are the muscles used for movement. Affected individuals experience muscle cramping and stiffening after exercise or other strenuous activity, especially in cold temperatures. These symptoms typically begin in childhood. They are usually painless, but in some cases can cause mild discomfort. The muscles usually relax after a few minutes of rest. Most commonly affected are the muscles of the arms, legs, and face (particularly the eyelids).

In some people with Brody myopathy, exercise leads to the breakdown of muscle tissue (rhabdomyolysis). The destruction of muscle tissue releases a protein called myoglobin, which is processed by the kidneys and released in the urine (myoglobinuria). Myoglobin causes the urine to be red or brown.

Mutations in the ATP2A1 gene cause Brody myopathy. The ATP2A1 gene provides instructions for making an enzyme called sarco(endo)plasmic reticulum calcium-ATPase 1 (SERCA1). The SERCA1 enzyme is found in skeletal muscle cells, specifically in the membrane of a structure called the sarcoplasmic reticulum. This structure plays a major role in muscle contraction and relaxation by storing and releasing positively charged calcium atoms (calcium ions). When calcium ions are transported out of the sarcoplasmic reticulum, muscles contract; when calcium ions are transported into the sarcoplasmic reticulum, muscles relax. The SERCA1 enzyme transports calcium ions from the cell into the sarcoplasmic reticulum, triggering muscle relaxation.

ATP2A1 gene mutations lead to the production of a SERCA1 enzyme with decreased or no function. As a result, calcium ions are slow to enter the sarcoplasmic reticulum and muscle relaxation is delayed. After exercise or strenuous activity, during which the muscles rapidly contract and relax, people with Brody myopathy develop muscle cramps because their muscles cannot fully relax.

Normal Function

The ATP2A1 gene provides instructions for making an enzyme called sarco(endo)plasmic reticulum calcium-ATPase 1 (SERCA1). This enzyme belongs to a family of ATPase enzymes that help control the level of positively charged calcium atoms (calcium ions) inside cells. The SERCA1 enzyme is found in skeletal muscle cells. (Skeletal muscles are the muscles used for movement.) Within muscle cells, the SERCA1 enzyme is located in the membrane of a structure called the sarcoplasmic reticulum. This structure plays a major role in muscle contraction and relaxation by storing and releasing calcium ions. When calcium ions are transported out of the sarcoplasmic reticulum, muscles contract; when calcium ions are transported into the sarcoplasmic reticulum, muscles relax. The SERCA1 enzyme transports calcium ions from the cell into the sarcoplasmic reticulum, triggering muscle relaxation.

Health Conditions Related to Genetic Changes

Brody myopathy

At least 10 mutations in the ATP2A1 gene have been found to cause Brody myopathy, a muscle disorder characterized by muscle cramping after exercise. Most ATP2A1 gene mutations lead to a premature stop signal in the instructions for making the SERCA1 enzyme, resulting in a nonfunctional enzyme. Other mutations lead to the production of a SERCA1 enzyme with decreased function. As a result, calcium ions are slow to enter the sarcoplasmic reticulum and muscle relaxation is delayed. After exercise or other strenuous activity, during which the muscles rapidly contract and relax, people with Brody myopathy develop muscle cramps because their muscles cannot fully relax. Scientists believe that other proteins or other pathways may function in the absence of a fully functional SERCA1 enzyme to transport calcium ions into the sarcoplasmic reticulum and help with muscle relaxation.

Other Names for This Gene

• AT2A1_HUMAN
• ATP2A
• ATPase, Ca++ transporting, cardiac muscle, fast twitch 1
• calcium-transporting ATPase sarcoplasmic reticulum type, fast twitch skeletal muscle isoform 1
• endoplasmic reticulum class 1 Ca2+ ATPase
• sarcoplasmic/endoplasmic reticulum calcium ATPase 1
• SERCA1
• SR Ca2+ ATPase 1

Genomic Location

• 25% (1 in 4) chance to be affected
• 50% (1 in 2) chance to be an unaffected carrier like each parent
• 25% (1 in 4) chance to be unaffected and not be a carrier

• Physical examination
• Bloodwork to evaluate the level of certain proteins such as creatine kinase
• Muscle biopsy
• Electromyography