DOCUMENT

16 | InTouch AUTUMN 2023 Spinal muscular atrophy (SMA) is a genetic disorder that affects the control of muscle movement. Spinal muscular atrophy (SMA) is caused by a loss of specific cells in the brainstem and spinal cord called alpha motor neurons. Motor neurons transmit signals from the brain and spinal cord to muscle fibres and are essential for muscle strength and movement. The loss of functioning motor neurons results in progressive weakness and atrophy of muscles used for activities such as crawling, walking, sitting up, and controlling head movement. The muscles used for breathing and swallowing may also be affected. Approximately 1 in 10,000 babies are born with SMA, and it affects boys and girls equally. There is a broad spectrum of SMA phenotypes ranging from severe antenatal onset to milder adult onset. Classification has historically been based on the age of onset and the highest motor developmental milestone achieved in the absence of disease-modifying therapy. Management has largely been limited to supportive measures, but the recent advent of disease-modifying therapies has changed the clinical approach to patients with SMA. SMA phenotypes SMA type 0 designates antenatal onset which typically presents with decreased fetal movement and severe weakness and hypotonia at birth. No motor milestones are achieved, and death can occur within one month due to respiratory failure. SMA type 1 (also called Werdnig- Hoffman disease) is a severe form Spinal Muscular Atrophy YOUR CONDITION IN REVIEW of the disorder that is evident within the first 6 months of life. An affected infant is delayed in all motor milestones and is unable to support their head or sit unassisted. Cognition and level of alertness are normal. Facial weakness is minimal or absent. Tongue fasciculations (twitching involuntary muscle contractions) are often present. Breathing and swallowing problems may lead to choking or gagging. It is unusual for these children to live past 2 years without intervention with disease- modifying or gene therapy. SMA type 2 is characterized by muscle weakness that develops in children between ages 6 and 18 months. Children with type 2 can sit without support, although they may need help getting to a seated position. Individuals with this type of spinal muscular atrophy cannot stand or walk unaided. As in all other subtypes, cognition is normal and may be above average by adolescence. Some develop restrictive lung disease secondary to significant scoliosis. SMA type 3 (also called Kugelberg- Welander disease or juvenile type) has milder features that typically develop between early childhood and adolescence. This group is sometimes subdivided into type 3A (onset before age 3) and type 3B (onset after age 3). Individuals with type 3 spinal muscular atrophy can stand and walk unaided but walking and climbing stairs may become increasingly difficult. Legs are more severely affected than the arms and many will require wheelchair assistance later in life. They do not develop significant respiratory or orthopedic problems. SMA type 4 is characterized by adult onset and slow progression. Affected Spinal muscular atrophy (SMA) is caused by a loss of specific cells in the brainstem and spinal cord called alpha motor neurons. Mode of inheritance.