Snapshot An infant is brought to the pediatrician by his mother due to muscle weakness. The mother reports that the infant’s weakness has progressively worsened. He is unable to sit unsupported, has a weak cry and suck. On exam, there is fasciculations of the tongue and fingers with absent deep tendon reflexes. Molecular genetic testing for the SMN gene is ordered. Introduction Also known as infantile spinal muscle atrophy (SMA) most common and severe of the SMA disorders degeneration of the anterior horn → muscle weakness lower brain stem and spinal cord autosomal recessive mutation in the SMN1 gene may present in utero mother may notice decreased (or absent) fetal movement late in pregnancy Epidemiology Commonly presents in the neonatal period Median survival is 7 months onset at birth Presentation Symptoms symmetric flaccid paralysis most affected infants are hypotonic at birth proximal muscle involvement lower extremity greater than upper extremity sparing of upper cranial nerves e.g., normal eye movements Physical exam absent or decreased deep tendon reflexes tongue and finger fasciculatons infants have flaccid "frog like" posture restrictive respiratory insufficiency Evaluation Molecular genetic testing confirms the diagnosis Electromyography (EMG) fibrillations and sharp waves Muscle biopsy Differential Congenital myasthenia syndromes Congenital myopathy Treatment Supportive ensure nutritional support and respiratory assistance manage weakness Prognosis, Prevention, and Complications 95% death by 18 months of age and 100% by four years of age Development of kyphosis and scoliosis Weakened pulmonary muscles decreased respiratory support from musculature can lead to hypoxia and CNS damage Malnutrition from difficulty in food intake Immobility combination of muscle weakness and degeneration along with a host of other orthopedic problems such as scoliosis