Spinal muscle atrophy is a genetic disorder characterized by the wasting or weakness of the muscles used for mobility. It is caused by the loss of motor neurons (nerve cells that aid in the control of muscle movement). This occurs more in proximal muscles than in distal muscles. 

Here are some of the rare types of spinal muscle atrophy:

Distal hereditary motor neuropathy type 5

• Distal hereditary motor neuropathy type 5 is a type of spinal muscular atrophy that is very rare.
• It is a progressive disorder that destroys the nerve cells in the spinal cord.
• This results in the weakness of muscles that aid in the movement of your hands and feet.
• It usually originates during adolescence but can occur at any age.
• The most common symptom and one of the first to show up is the cramps in hand due to cold temperatures.

Spinal and bulbar muscular atrophy 

• Spinal and bulbar muscular atrophy, commonly known as Kennedy disease, is a disorder of motor neurons.
• This condition mainly affects males and is characterized by the wasting of muscles that progresses over time.
• Muscles that weaken and waste in the legs and arms can result in cramps and poor balance.
• Certain muscles in the face and throat are also affected, causing problems with speech and swallowing. Your face may also start twitching involuntarily.
• Some men with this condition may experience gynecomastia and infertility.

Spinal muscular atrophy with lower extremity dominance 

• Spinal muscular atrophy with lower extremity dominance is named so because it affects the lower limbs.
• It is characterized by the wastage and weakening of the muscles in your legs, especially your thighs.
• People affected by the condition often find it difficult to walk and have proper balance.
• They have difficulty getting up from a seated position, climbing the stairs, and any other activity that requires the strength of the lower body.
• Joint deformities can occur in the hips, feet, and knees.
• If this condition affects an individual at birth, they may have impaired legs for the rest of their life.
• The chance of this condition affecting you when you are an adult is only 25%, as most people develop this condition during infancy.

Spinal muscular atrophy with progressive myoclonic epilepsy 

• Spinal muscular atrophy with progressive myoclonic epilepsy is a type of spinal muscular atrophy characterized by the combination of the wasting of skeletal muscles and a set of seizures and muscle jerks (myoclonic epilepsy)
• The lower limbs are affected first, after which the upper limbs slowly lose their muscles.
• After a good amount of time, the atrophy spreads throughout the body.
• A few years after the disorder originates, individuals start to experience persistent seizures and muscle jerks.
• Some people develop a hearing loss due to the nerve damage in the inner ear.
• Most of these patients pass away at an early stage of life due to the shortened lifespan that accompanies this disorder.

X-linked infantile SMA 

• This is a type of spinal muscle atrophy that affects only the male gender.
• Affected children have areflexia, severe muscle weakness, contractures, and arthrogryposis from birth.
• The weakness of the chest muscles can lead to life-threatening situations.
• Unfortunately, most of these patients can barely survive until early childhood, and in rare cases, they make it to adolescence.