Heredity Disorders

Hereditary motor or sensory neuropathies refer to a group of nerve disorders that lead to weakness and wasting of the muscles generally below the knees, and in the hands, and that may be passed from parents to children. For several of these conditions, the genetic defect is known, and tests are available for diagnosis and prenatal counseling.

Two hereditary neuropathies are:

Charcot-Marie-Tooth disease (CMT) is a broad term used to describe a group of inherited neurological disorders characterized by a slowly progressive degeneration of the muscles in the foot, lower leg, hand, and forearm, and a mild loss of sensation in the limbs, fingers, and toes.

Three French doctors, Jean-Marie Charcot, Pierre Marie, and Howard Henry Tooth, discovered CMT in 1886. Although CMT is one of the most common inherited neuromuscular disorders, it is often misdiagnosed. The number of people in the United States that have CMT is currently estimated to be 125,000.

The symptoms of CMT depend on which form of the disease is inherited, but generally start between mid-childhood and early adulthood. The first signs are usually foot abnormalities, such as an unusually high arch or flexed (“hammer”) toes. People with CMT often trip on curbs. Sprained ankles and fractures of the ankles and lower legs are not uncommon. As the disease progresses, muscle weakness and wasting leads to difficulties with walking, running and balance. If the hands are affected, daily activities such as turning doorknobs, fastening buttons, or writing can become difficult.

The disease is slowly progressive and, although many patients need to wear a brace to prevent their feet from dragging, the leg and foot problems are rarely disabling enough to require a wheelchair. CMT is not a fatal disease and the disorder does not affect normal life expectancy.

TYPES 1, 2, AND 3 OF CMT

CMT is usually divided into types 1 and 2, depending on which part of the peripheral nerve is affected. The majority of people have type 1, which affects the myelin sheath (the protective covering of the nerve). About one-third of people with CMT have type 2, which affects the nerve fibers (axons) themselves.

An especially severe form of CMT, sometimes referred to as type 3 CMT, is also known as Déjerine-Sottas disease, after the two French doctors who discovered it in the late 19th century. With Déjerine-Sottas disease, the peripheral nerves become enlarged or thickened, leading to muscle weakness. The symptoms often show up in infancy and progressively affect a child’s ability to walk.

How is it inherited? At least four genes have been discovered to be the cause of CMT. CMT usually is inherited in an autosomal dominant pattern, which means that each child that has a parent with CMT has a 50% chance of inheriting the disease. It can also be inherited in a recessive or an X-linked pattern.

Symptoms & Signs

(Not all symptoms and signs may be present.)

Symptoms range in patients from very mild to severe weakness; clinical symptoms generally occur by age 30. The more severe symptoms are related to an earlier age of onset. CMT can progress to extreme weakness, atrophy, and loss of sensation, over time.

  • Foot drop (foot can’t be picked up or held horizontal)
  • Progressive deformity of leg (“inverted champagne bottle”) or foot (abnormally high arched feet, flat feet, hammer toes)
  • Decreased sensation or numbness in the foot or leg
  • Awkward gait and balance
  • Poor hand coordination

Evaluation & Tests

(Not all evaluation and tests may be necessary.)

The disease is frequently undiagnosed or misdiagnosed because many physicians are not aware of CMT and because the severity of CMT can vary between patients, even within the same family. The diagnostic evaluation includes a clinical assessment of muscle strength, reflexes, and sensation.

For diagnosis of foot fracture:

  • X-ray
  • Bone scan

Treatment & Therapy

(Not all treatments and therapies may be indicated.)

Although there is no cure for CMT, physical therapy, occupational therapy and moderate physical activity may help maintain muscle strength and endurance. Lightweight lower leg braces, special shoes or shoe inserts can help prevent ankle sprains and maximize independence. Surgery may be suggested to correct foot deformities.

Treatment options may include:

  • Over-the-counter pain medication for mild pain
  • For severe pain, take over-the-counter pain medication or prescription drugs used for peripheral neuropathy, on a regular basis—rather than waiting until nighttime when symptoms can become more severe
  • Special therapeutic shoes (which may be covered by Medicare and other insurance)
  • Leg braces
  • Physical therapy
  • Moderate activity
  • Surgery
  • Take safety measures to compensate for loss of sensation

Hereditary neuropathy with liability to pressure palsies (HNPP) is a relatively common, though under-diagnosed, hereditary disorder in which a fairly mild pressure or trauma to a single nerve results in episodes or periods of numbness and weakness, similar to an arm or leg going to sleep. Unlike a limb going to sleep for a few seconds, each episode of numbness can last from several minutes to several days or months. The most common sites are the wrists, with carpal tunnel syndrome, or the elbows or knees. HNPP is inherited in an autosomal dominant manner, which means that each child of a person with HNPP has a 50% chance of inheriting the genetic mutation. It may be misdiagnosed as Charcot-Marie Tooth disease or Bell’s palsy.

HNPP is a progressive hereditary disorder, but the symptoms can be so mild that they go unnoticed. For some people, there are years between episodes, while others have mild symptoms that progress at a steady rate.

There is no treatment other than symptomatic measures and avoiding positions that can create pressure such as leaning on elbows, crossing legs or ankles, or sitting for too long without changing position.

Symptoms & Signs

(Not all symptoms and signs may be present.)

  • Weakness—unable to move an entire limb
  • Unable to use certain muscles of the arm (can’t reach, wash hair, eat) or hand (difficulty gripping things or grasping small objects) or face
  • Episodes of numbness, weakness or tingling that do not go away
  • Leg/ankle foot swelling
  • Fatigue
  • Muscle cramps
  • Diminished or absent ankle reflexes

Evaluation & Tests

(Not all evaluation and tests may be necessary.)

Treatment & Therapy

(Not all treatments and therapies may be indicated.)

  • For severe pain, take over-the-counter pain medication or prescription drugs used for peripheral neuropathy, on a regular basis—rather than waiting until nighttime when symptoms can become more severe
  • Avoid prolonged activity on hands and knees that could cause nerve compression
  • Avoid crossing legs at the knee
  • Avoid sitting with legs crossed, tailor-style
  • Avoid sitting in one position too long without readjusting
  • Avoid holding the telephone in one position too long
  • Avoid tying shoes too tight or using tight shoe straps
  • Avoid high heels (even 1 inch), which can make toes numb
  • Take safety measures to compensate for loss of sensation
  • Ask your doctor about special therapeutic shoes (which may be covered by Medicare and other insurance).