SPINAL MUSCULAR ATROPHY

Spinal Muscular Atrophy (SMA), or spinal amyotrophy, is a neuromuscular disease characterized by the progressive degeneration and death of motor neurons in the spinal cord and brainstem. Normally, motor neurons - located in the brain and spinal cord - send signals to the body's muscles, instructing them to contract and move. In people with spinal muscular atrophy, these neurons deteriorate and die, meaning muscles no longer receive the necessary signals to contract. As a result, muscles begin to atrophy - or weaken - and the person loses the ability to control voluntary movements. This leads to difficulties in performing simple movements, such as walking or moving arms, as well as problems with breathing, swallowing, and controlling the head and neck. Depending on the type of SMA, symptoms can appear at birth or later in life.[1][2]

Types of Spinal Muscular Atrophy

Depending on the age of onset and the severity of symptoms, there are four main types of spinal muscular atrophy:

• type 1 spinal muscular atrophy (Werdnig-Hoffman disease) is the most severe and most common, with onset in the first months of life; in many cases, death occurs before the age of 2;
• type 2 spinal muscular atrophy (Dubowitz disease) manifests between the ages of 6 and 18 months, and progression is slower; life expectancy is variable, but many survive to adulthood;
• type 3 spinal muscular atrophy (juvenile SMA or Kugelberg-Welander syndrome) begins after the age of 18 months, and life expectancy is almost normal;
• type 4 spinal muscular atrophy, the adult-onset form, represents the rarest and least severe type of spinal amyotrophy; it generally appears in the third decade of life and progression is slow; life expectancy is normal.[1][2]

Causes of Spinal Muscular Atrophy

Spinal Muscular Atrophy (SMA) is caused by a genetic mutation in the SMN1 gene, which plays a crucial role in the normal function of muscles. This gene is responsible for producing the SMN protein, essential for normal muscle contraction and control of movements of the limbs, abdominal muscles, head, neck, and respiratory muscles. The mutation of the SMN1 gene causes a deficiency of this protein, leading to spinal muscular atrophy.[1]

In most cases, a child can be born with SMA only if both parents are carriers of the mutant gene. Thus, if two parents are carriers of the mutant gene, there is a 25% chance their child will have SMA, a 50% chance the child will be a carrier of the gene but not show the disease, and a 25% chance the child will neither have SMA nor be a carrier. There are also rarer cases of SMA, which can be inherited in a different manner or may not be transmitted at all.[2]

Signs and Symptoms of Spinal Muscular Atrophy

Symptoms of spinal muscular atrophy can vary from person to person, depending on the type of spinal muscular atrophy they have. In general, however, it is characterized by progressive muscle weakness, particularly in the lower limbs, muscle atrophy, difficulties in walking, sitting up, or lifting the head, swallowing and respiratory disorders, and persistent fatigue. Sometimes, this condition can also lead to spinal deformities.[1][2][3]

Symptoms of SMA type 1

Babies with type 1 spinal muscular atrophy (SMA1):

• have low muscle tone (hypotonia); 
• have problems with sucking, breathing, and swallowing;
• cannot hold their head up or sit without support.[2]

Symptoms of SMA type 2

Children with this type of spinal muscular atrophy:

• can sit but cannot stand or walk;
• may exhibit hand and finger tremors;
• show muscle deficit in the limbs;
• may have skeletal deformities such as scoliosis;
• are prone to respiratory infections.[2]

Symptoms of SMA type 3

In this type of spinal muscular atrophy, affected individuals:

• can walk and stand up, but may face difficulties when it comes to climbing or descending stairs, running, or getting up from a sitting position;
• encounter muscle weakness and frequent respiratory infections.[2]

Symptoms of SMA type 4

This type of spinal amyotrophy is characterized by:

• muscle weakness;
• difficulties in walking;
• muscle tremors and twitches.

Symptoms worsen slowly over time, but normally there are no problems with breathing or swallowing.[2]

Treatment Options for Spinal Muscular Atrophy

Although there is no definitive treatment for spinal muscular atrophy (SMA), there are several options that can alleviate symptoms, slow disease progression, and improve the quality of life for patients.

Gene therapies

Gene therapies involve using innovative technologies to correct or replace the defective genes that cause spinal muscular atrophy. However, it is important to note that gene therapies are still in the research phase and are not available for all patients.[2]

Respiratory management

Spinal muscular atrophy can significantly affect the muscles that aid in breathing, making it difficult for affected individuals to breathe. Patients with breathing difficulties may require non-invasive ventilation to prevent sleep apnea, while others may need assisted ventilation during the day as well.[2]

Management of feeding and nutrition

Adequate nutrition and calories are essential for maintaining weight and strength, while avoiding prolonged fasting. People who cannot chew or swallow may require the insertion of a feeding tube.

A nasogastric tube (a flexible plastic tube that is inserted through one of the nostrils, passes through the pharynx and esophagus, reaching the stomach, usually used for short-term feeding) or a gastrostomy (an endoscopic procedure that involves placing a flexible tube for feeding the patient directly into the stomach) may be used.[1][2]

Orthopedic treatment of joint and spinal deformities

May include:

• physical therapy and physiotherapy - the rehabilitation plan is individualized and focuses on improving function and mobility;
• the use of orthoses and assistive devices to improve posture, walking, and motor function (e.g., walking frames, ankle orthoses, spinal corsets, crutches, wheelchair);
• surgical interventions - in severe cases, surgical interventions may be necessary to correct scoliosis; surgeries may also be recommended to improve joint function or to stabilize the spine.[1][2]

Pain management

Pain can arise from muscle contractures, bone deformities, or other complications of SMA. Various methods can be used to reduce pain, including analgesics, physiotherapy, and relaxation techniques.[4]

Spinal Muscular Atrophy is a complex disease that requires a multidisciplinary approach. Managing the disease may involve a team of specialists who will establish a treatment plan that can help maximize the quality of life for individuals with spinal muscular atrophy.

Spinal Muscular Atrophy can have a major impact on quality of life, characterized by the degeneration of motor neurons and impairment of muscle function. Despite the fact that there is currently no treatment to completely cure this disease, there are methods to alleviate symptoms and support patients and their families.

References: 

1. „Spinal Muscular Atrophy”, National Institute of Neurological Disorders and Stroke, 2024. Accessed 15 Feb. 2024.
2. „Spinal Muscular Atrophy”, NHS, 2024. Accessed 15 Feb. 2024.
3. „Spinal Muscular Atrophy (SMA): Types, Symptoms & Treatment”, Cleveland Clinic, 2021. Accessed 15 Feb. 2024.
4. Yuu UCHIO, et al. „Pain in Spinal Muscular Atrophy: A Questionnaire Study.” Physical Therapy Research, vol. 25, no. 3, 1 Jan. 2022, pp. 150–155, https://doi.org/10.1298/ptr.e10201. Accessed 15 Feb. 2024.