Spinal Muscular Atrophy Neonatal Screening Program

Spinal muscular atrophy (SMA) is a group of disorders caused by the degeneration of the motor neuron cells of the anterior horn of the spinal cord and, in some subtypes, of the bulbar motor neurons. Almost all cases are genetically determined. Most SMAs are autosomal recessive diseases, caused by homozygous deletions of the survival motor neuron (SMN) gene located on the long arm of chromosome 5. The estimated incidence of recessive childhood and juvenile SMA linked to deletion of the SMN gene is 1 in 6000 to 10000 live births, with a carrier frequency of 1 in 35 in the general population, making it a major genetic cause of infant mortality. Up to 95-97% of all childhood cases are due to homozygous deletions of the survival motor neuron 1 (SMN1) gene, or telomeric SMN, located on chromosome 5q11.2-13.3. The remaining 3-5% of cases are due to small mutations in SMN1 (rather than complete deletions).

Until a few years ago, the prognosis of type 1 SMA was poor. In the absence of therapies, the only measures were supportive (ventilation, nutrition) and the prospect, especially in the early forms, was to accompany them towards an early end of life. There are currently three treatment options available: nusinersen, risdiplam, and gene therapy with onasemnogene abeparvovec. The three options were found to be equally effective in reducing the symptoms of the disease, making it possible to reach or safeguard fundamental stages in a child's neuromotor development, starting from the ability to remain seated. At this moment, gene therapy is probably the preferred choice. To date, in Italy, there are approximately 100 patients undergoing gene therapy.

To ensure maximum benefit for affected patients, it is essential that the therapy is administered as soon as possible. Literature shows how the administration of gene therapy in pre-symptomatic subjects made it possible to achieve a better neurological outcome compared to symptomatic patients. From this perspective, the inclusion of spinal muscular atrophy in neonatal screening is of fundamental relevance.