SMA type 3, or spinal muscular atrophy type 3, is a genetic disorder that affects motor neurons in the spinal cord. It is characterized by muscle weakness and atrophy, primarily impacting the legs and proximal muscles. Symptoms usually appear between the ages of 18 months and 3 years, and individuals may have difficulty walking or climbing stairs. This condition is caused by a deficiency in the survival motor neuron (SMN) protein due to mutations in the SMN1 gene. While SMA type 3 is generally milder than other types, individuals may experience progressive weakness over time. Early diagnosis and supportive therapies can help improve quality of life.