General movements in spinal muscular atrophy type 1

Area of Science:

• Pediatric Neurology
• Developmental Neuroscience
• Movement Disorders

Background:

• Spinal Muscular Atrophy Type I (SMA Type I) is a severe neuromuscular disorder affecting motor neuron development.
• Understanding the early motor repertoire in untreated SMA Type I is crucial for assessing disease impact and potential interventions.

Purpose of the Study:

• To characterize the motor repertoire of infants diagnosed with SMA Type I before disease-modifying treatments.
• To compare the motor skills of infants with SMA Type I to those with cerebral palsy (CP) and typical development.

Main Methods:

• The study analyzed videos of 22 infants with SMA Type I between post-term weeks 9-17.
• The Motor Optimality Score-Revised (MOS-R) was calculated for each infant.
• MOS-R scores were compared between infants with SMA Type I, CP, and typical development.

Main Results:

• Most infants with SMA Type I (17/22) lacked fidgety movements (FMs); 5 had sporadic FMs.
• The motor repertoire was age-inadequate, with low movement variety, symmetrical limb movements, rare antigravity movements, and monotonous, slow, small-amplitude movements.
• Infants with SMA Type I had lower MOS-R scores than typically developing infants but similar scores to infants with CP.

Conclusions:

• Infants with SMA Type I demonstrate a motor repertoire comparable to infants with CP and significantly poorer than typically developing infants during the fidgety period.
• The extent of central nervous system involvement in SMA Type I, particularly with absent FMs and reduced MOS-R, requires further investigation.
• Future research should explore the contribution of spinal cord pathway issues and muscle atrophy to the observed motor deficits and lack of normal FMs.