Children with spinal muscular atrophy type 2 saw a marked improvement in hand and finger dexterity after 18 months of treatment with nusinersen, according to a recent study out of South Korea. Participants’ gross motor skills — sitting, rolling, and crawling — also improved during the course of the study.
The study is the first of its kind to investigate the effects of nusinersen on fine manual dexterity in children with SMA type 2, according to researchers from Chungbuk National University Hospital. Previous studies have determined that nusinersen can improve gross motor function in people with SMA.
“Considering that most patients with SMA type 2 cannot stand alone or walk with assistance, even if they receive nusinersen treatment, fine manual dexterity is important for activities of daily living in these patients,” the study notes.
SMA is a genetic disorder caused by mutations in the survival motor neuron (SMN) genes. These genes encode for proteins that are necessary for muscles to send electrical signals from the brain to the muscles — with this, they play a large role in movement and dexterity.
SMA symptom severity tends to correlate with the age that a person is diagnosed. For example, children diagnosed with SMA type 2 typically begin to show symptoms between the ages of 6 months and 12 months. Children with SMA type 2 typically have difficulty controlling their fingers due to involuntary tremors.
Spinraza is approved by the U.S. Food and Drug Administration (FDA) to treat all types of SMA in all people of all ages. Several studies have shown that nusinersen improves gross motor skills, but it has never been studied for its effects on fine motor skills, such as grasping and manipulating objects.
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In total, five children with confirmed SMA type 2 were included in the study. After receiving four loading doses of Spinraza, the children continued to receive maintenance doses every four months. Functional tests were performed before beginning treatment, between the third and fourth loading doses, and before every dose during the maintenance period. In total, the children were evaluated over 18 months.
The authors used the Purdue Pegboard (PP) test as a standardized measurement of fine motor skills and dexterity. The children are tasked with picking pegs from a cup and placing them into holes on a pegboard as quickly as possible for 30 seconds. The number of pegs placed is used as a measure of fine motor dexterity.
PP scores were measured before nusinersen treatment and after 18 months. The scores improved for all of the children by 80 to 225 percent when compared to their baseline scores.
The authors also measured the childrens’ gross motor function using the Hammersmith Functional Motor Scale (HFMSE) to look at improvements in sitting, rolling, lying, and crawling. HFMSE scores were taken before nusinersen treatment and after 18 months. These scores improved for all of the children by 13 to 53 percent when compared to baseline.
Overall, nusinersen treatment significantly improved fine motor skills and some gross motor skills in children with SMA type 2. The authors noted some limitations, writing, “Since this study was conducted only on patients with SMA type 2, the effect of nusinersen on fine manual dexterity in patients with other subtypes of SMA could not be identified.”
Future studies with more participants will be needed to determine if results would be similar in other types of SMA.