Presymptomatic risdiplam treatment in an infant with homozygous SMN1 deletion and two SMN2 copies: age-appropriate motor development at 6 months

Spinal muscular atrophy (SMA) is a progressive neuromuscular disorder caused by biallelic SMN1 deletion or mutation, leading to degeneration of anterior horn motor neurons. Newborn screening enables presymptomatic diagnosis, and timely initiation of disease-modifying therapy is associated with improved outcomes. Risdiplam is an oral SMN2 pre‑mRNA splicing modifier approved for SMA across a broad age range. A male infant with a positive newborn screening result was referred at 10 days of age. Confirmatory testing demonstrated a homozygous SMN1 exon 7 deletion with two copies of SMN2. Neurological examination revealed generalized areflexia with otherwise normal spontaneous antigravity movements. Due to administrative issues, risdiplam was initiated at 1 month of age. Before treatment initiation, the CHOP-INTEND score was 28/64. At 6 months of age, repeat assessment showed an increase to 41/64; both evaluations were performed by the same experienced physiotherapist. At 6 months, gross motor development was age-appropriate; deep tendon reflexes remained absent, and no bulbar or respiratory involvement was observed. This case supports that early presymptomatic risdiplam initiation may be associated with near‑typical early motor development in infants with two SMN2 copies, although residual signs such as areflexia can persist. Efforts should focus on minimizing delays, with the goal of initiating therapy as early as possible after birth (ideally within the first two weeks).