Spinal muscular atrophy (SMA) is an uncommon inherited neuromuscular condition marked by gradual degeneration of lower motor neurons in the spinal cord and brainstem that govern voluntary muscles. Loss of these cells causes muscles to weaken and shrink, impairing sitting, standing, walking, swallowing and, in serious cases, breathing.
SMA affects roughly one to two people per 100,000, with a birth rate of one in 6,000 to one in 10,000 live births, ranking among the more frequent inherited neuromuscular disorders in early life. Incidence among Asian Indians stands at one in 9,655 births, while carrier frequency is one in 71.
The majority of cases result from alterations in the SMN1 gene that produces a protein needed for motor neuron survival. About 95 percent of common 5q SMA cases involve homozygous deletion of exon 7 in SMN1. Disease severity depends on SMN2 gene copy number, which yields limited amounts of the same protein. Physicians group SMA into types 0-4 according to symptom onset age and peak motor function reached, with type 1 comprising roughly half of cases.
Access to diagnosis and treatment remains difficult in many nations including India, yet prompt intervention can improve survival, motor ability and life quality, especially when begun before symptoms emerge.
Signs and symptoms differ by type and severity. Severe infant forms may feature low muscle tone, poor head control, feeding and swallowing issues, and breathing problems. Milder childhood or adult forms can involve delayed motor milestones, trouble standing or walking, repeated falls, fatigue and progressive weakness that usually begins near the body core before affecting limbs. Sensation and cognition are typically preserved.
Physicians often identify SMA through symptoms, developmental history and neurological exams, confirmed by genetic testing for SMN1 changes. Several countries run newborn screening programs since treatment works best before symptoms and irreversible neuron loss occur.
SMA follows autosomal recessive inheritance, so a child must inherit altered SMN1 copies from both parents. Carrier parents usually show no symptoms. Each pregnancy carries a 25 percent chance of SMA, 50 percent chance of carrier status and 25 percent chance of no altered copies. While SMA can affect any sex or background, fewer SMN2 copies correlate with severe early-onset disease.
No cure exists, but therapies developed in the last decade either replace the faulty SMN1 gene or raise survival motor neuron protein from SMN2. Studies show best results when treatment starts early, ideally before symptoms. Supportive care including respiratory aid, nutrition, physiotherapy, occupational therapy and orthopaedic support remains vital and is delivered by multidisciplinary teams. Experts continue urging wider genetic testing access, earlier diagnosis and comprehensive care.
