TTN Gene

Tibial muscular dystrophy is a condition that affects the muscles at the front of the lower leg. The signs and symptoms of this condition typically appear after age 35. The first sign is usually weakness and wasting (atrophy) of a muscle in the lower leg called the tibialis anterior. This muscle helps control up-and-down movement of the foot. Weakness in the tibialis anterior muscle makes it difficult or impossible to walk on the heels, but it usually does not interfere significantly with regular walking.

Muscle weakness worsens very slowly in people with tibial muscular dystrophy. Ten to 20 years after the onset of symptoms, weakness may develop in muscles that help extend the toes (long-toe extensors). Weakness in these muscles makes it difficult to lift the toes while walking, a condition known as foot drop. Later in life, about one third of people with tibial muscular dystrophy experience mild to moderate difficulty with walking because of weakness in other leg muscles. However, most affected individuals remain able to walk throughout their lives.

A small percentage of people with tibial muscular dystrophy have a somewhat different pattern of signs and symptoms than those described above. Starting in childhood, these individuals may have generalized muscle weakness, weakness and atrophy of the thigh muscles (quadriceps) or other muscles in the legs, and weakness affecting muscles in the arms.

Early-onset myopathy with fatal cardiomyopathy (EOMFC) is an inherited muscle disease that affects the skeletal muscles, which are used for movement, and the heart (cardiac) muscle. This condition is characterized by skeletal muscle weakness that becomes apparent in early infancy. Affected individuals have delayed development of motor skills, such as sitting, standing, and walking. Beginning later in childhood, people with EOMFC may also develop joint deformities called contractures that restrict the movement of the neck and back. Scoliosis, which is an abnormal side-to-side curvature of the spine, also develops in late childhood.

A form of heart disease called dilated cardiomyopathy is another feature of EOMFC. Dilated cardiomyopathy enlarges and weakens the cardiac muscle, preventing the heart from pumping blood efficiently. Signs and symptoms of this condition can include an irregular heartbeat (arrhythmia), shortness of breath, extreme tiredness (fatigue), and swelling of the legs and feet. The heart abnormalities associated with EOMFC usually become apparent in childhood, after the skeletal muscle abnormalities. The heart disease worsens quickly, and it often causes heart failure and sudden death in adolescence or early adulthood.

Hereditary myopathy with early respiratory failure (HMERF) is an inherited disease that affects muscles used for movement (skeletal muscles) and muscles that are needed for breathing (respiratory muscles).

The major signs and symptoms of HMERF usually appear in adulthood, often in the mid-thirties. Among the earliest signs of the condition are breathing problems and difficulty walking. Weakness of the respiratory muscles, particularly the diaphragm (the muscle that separates the organs in the abdomen from those in the chest), causes breathing problems. This weakness worsens over time and can lead to life-threatening respiratory failure. Some affected individuals have weakness of muscles of the lower leg and foot, which makes it difficult to lift the toes while walking, a condition known as foot drop. Other muscles that become weak in people with HMERF include those of the hips, thighs, upper arms, and neck.

When viewed under a microscope, muscle fibers from affected individuals contain abnormal structures called cytoplasmic bodies. In many cases, the cytoplasmic bodies are arranged side-by-side in a ring inside the muscle fiber, resembling a necklace (necklace cytoplasmic bodies).

Familial dilated cardiomyopathy is a genetic form of heart disease. It occurs when heart (cardiac) muscle becomes thin and weakened in at least one chamber of the heart, causing the open area of the chamber to become enlarged (dilated). As a result, the heart is unable to pump blood as efficiently as usual. To compensate, the heart attempts to increase the amount of blood being pumped through the heart, leading to further thinning and weakening of the cardiac muscle. Over time, this condition results in heart failure.

It usually takes many years for symptoms of familial dilated cardiomyopathy to cause health problems. They typically begin in mid-adulthood, but can occur at any time from infancy to late adulthood. Signs and symptoms of familial dilated cardiomyopathy can include an irregular heartbeat (arrhythmia), shortness of breath (dyspnea), extreme tiredness (fatigue), fainting episodes (syncope), and swelling of the legs and feet. In some cases, the first sign of the disorder is sudden cardiac death. The severity of the condition varies among affected individuals, even in members of the same family.

Limb-girdle muscular dystrophy is a term for a group of diseases that cause weakness and wasting of the muscles in the arms and legs. The muscles most affected are those closest to the body (proximal muscles), specifically the muscles of the shoulders, upper arms, pelvic area, and thighs.

The severity, age of onset, and features of limb-girdle muscle dystrophy vary among the many subtypes of this condition and may be inconsistent even within the same family. Signs and symptoms may first appear at any age and generally worsen with time, although in some cases they remain mild.

In the early stages of limb-girdle muscular dystrophy, affected individuals may have an unusual walking gait, such as waddling or walking on the balls of their feet, and may also have difficulty running. They may need to use their arms to press themselves up from a squatting position because of their weak thigh muscles. As the condition progresses, people with limb-girdle muscular dystrophy may eventually require wheelchair assistance.

Muscle wasting may cause changes in posture or in the appearance of the shoulder, back, and arm. In particular, weak shoulder muscles tend to make the shoulder blades (scapulae) "stick out" from the back, a sign known as scapular winging. Affected individuals may also have an abnormally curved lower back (lordosis) or a spine that curves to the side (scoliosis). Some develop joint stiffness (contractures) that can restrict movement in their hips, knees, ankles, or elbows. Overgrowth (hypertrophy) of the calf muscles occurs in some people with limb-girdle muscular dystrophy.

Weakening of the heart muscle (cardiomyopathy) occurs in some forms of limb-girdle muscular dystrophy. Some affected individuals experience mild to severe breathing problems related to the weakness of muscles needed for breathing. In some cases, the breathing problems are severe enough that affected individuals need to use a machine to help them breathe (mechanical ventilation).

Intelligence is generally unaffected in limb-girdle muscular dystrophy; however, developmental delay and intellectual disability have been reported in rare forms of the disorder.