Peripheral nerves lie outside the brain and spinal cord and are responsible for directly stimulating muscle, transmitting sensations and controlling involuntary (autonomic) activities such as blood pressure. Disorders of peripheral nerves are frequently inherited. Common inherited peripheral neuropathies include Charcot-Marie-Tooth Disease (CMT), also known as Hereditary Motor and Sensory Neuropathy, Dejerine-Sottas Disease and Friedreich’s Ataxia.
Types and Symptoms
Charcot-Marie-Tooth Disease (CMT) - CMT describes a group of disordered caused by defects in the genes for various proteins found in the fibers that carry electrical signals between the brain and spinal cord and the rest of the body, called axons, or in the genes for proteins found in myelin, the covering that insulates axons. The onset of symptoms in CMT may occur at any time between birth and adulthood, depending in part on the type of CMT. Symptoms include muscle weakness and wasting as well as loss of sensation. These symptoms usually begin in the feet and slowly progress to include the lower legs, hands and forearms. There is often, but not always, a family history of weakness and loss of sensation.
Dejerine-Sottas Disease (DS) - DS is also known as CMT type 3 and is an inherited peripheral neuropathy with an onset in infancy. The disorder is caused by a defect in one of the genes for myelin and is marked by severe, progressive weakness and sensory loss. Children with DS acquire motor milestones slowly, and some never gain the ability to walk. Others begin walking at preschool age or later, but many require wheelchairs by their teen-age years. Scoliosis (curvature of the spine) and ataxia (lack of coordination and balance) are common.
Friedreich’s Ataxia (FA) - FA is a neurological disorder that also causes a peripheral neuropathy and damage to the cerebellum, a part of the brain that helps coordinate movement. The heart is also frequently affected in FA. The disorder is caused by a mutation in a gene that is important in mitochondrial function, resulting in decreased energy production in cells of the nervous system and heart. Symptoms frequently begin in teenage years and are slowly progressive. People with FA have difficulty with balance and coordination, loss of sensation in the legs and cardiac abnormalities.
Diagnosis and Treatment
People with inherited peripheral neuropathies are diagnosed based on their medical history, including a possible family history, clinical examination and supporting laboratory investigations. Laboratory investigations include electrophysiology (EMG and nerve conduction studies), occasionally nerve and muscle biopsies and, when appropriate, genetic testing. Our genetics counselor will carefully review the history of disease with each family, discuss the principles of inheritance and help weigh risks and benefits of genetic testing of various family members.
Treatment of inherited neuropathies is conducted by our multidisciplinary team of experts. The neurologist oversees the various needs of the patient and directs care to various subspecialities. Depending on the particular type of neuropathy, the neurologist may provide treatment for neuropathic pain with a variety of drugs such as gabapentin, amitriptyline and analgesics. Contractures, or decreased flexibility at the joints, are identified and treated with exercise programs demonstrated by our physiotherapists in the on the day of clinic visit. Also on the same day, the patient will be evaluated for the need for splints and orthotics to help with hand or foot function. Equipment needs as well as social and financial needs are addressed. Other services, such as from an orthopedic surgeon, for further treatment of contractures or scoliosis, or from a cardiologist, in the case of FA, are available as needed and are provided by physicians with special interest and expertise in MDA diagnoses.