Longitudinal Investigation of Early Motor Development in Neurofibromatosis Type 1

Abstract

Objective: Research indicates that children with neurofibromatosis type 1 (NF1) have weaknesses in fine and gross motor development in early childhood; however, little is known about the stability and developmental trajectory of motor functioning. We investigated (1) whether motor difficulties are evident and stable in the preschool period in children with NF1 and (2) whether there are particular patterns of motor development in this population.

Methods: Participants with NF1 and a control group of unaffected siblings were enrolled at ages 3-8 years and were assessed yearly. Motor functioning was assessed longitudinally using the Scales of Independent Behavior-Revised Motor Scale and the Differential Ability Scales-II Copying subtest. Wilcoxon sign tests were used to compare motor functioning at 3 or 4 years to 5 or 6 years old for children with NF1 seen during both time periods (N = 27). Linear mixed model growth curve analyses were used to compare trajectories for both children with NF1 (N = 62) and unaffected siblings (N = 37).

Results: Children with NF1 made relative gains in raw scores, but not standard scores, across measures. Growth curve analyses revealed a significant effect of NF1 status on gross motor, fine motor, and copying scores, as well as an age by NF1 status effect on fine and gross motor scores.

Conclusions: Motor difficulties are evident early in life in children with NF1. Though children with NF1 clearly acquire motor skills over time, they continue to fall behind unaffected siblings, with the gap potentially widening over time. Further implications are discussed.

Keywords: genetics and genetic disorders; infancy and early childhood; longitudinal research; preschool children.

Figure 1.

Loess Lines of Scales of Independent Behavior—Revised (SIB-R) fine motor raw scores in neurofibromatosis type 1 (NF1) and unaffected sibling groups. Note. The Loess Lines of SIB-R Fine Motor raw scores depict an overlap in functioning across the two groups until about age 6.5. Afterwards, the unaffected sibling group’s scores are significantly better. NF1 group sample sizes: 3 years = 23, 4 years = 30, 5 years = 35, 6 years = 30, 7 years = 15, and 8 years = 17. Unaffected sibling group sample sizes: 3 years = 10, 4 years = 17, 5 years = 12, 6 years = 12, 7 years = 10, and 8 years = 8.

Figure 2.

Loess Lines of Scales of Independent Behavior—Revised (SIB-R) Gross Motor raw scores in neurofibromatosis type 1 (NF1) and unaffected sibling groups. Note. The Loess Lines of SIB-R Gross Motor raw scores depict an overlap in functioning across the two groups until about age 5.5. After age 5.5, the unaffected sibling group’s scores are significantly better. NF1 group sample sizes: 3 years = 23, 4 years = 30, 5 years = 35, 6 years = 30, 7 years = 15, and 8 years = 17. Unaffected sibling group sample sizes: 3 years = 10, 4 years = 17, 5 years = 12, 6 years = 12, 7 years = 10, and 8 years = 8.

Figure 3.

Loess Lines of Differential Ability Scales-Second Edition (DAS-II) Copying Ability scores in neurofibromatosis type 1 (NF1) and unaffected sibling groups. Note. The above Loess Lines depict no overlap in DAS-II Copying Ability scores across time, with the unaffected group consistently performing better than the NF1 group. NF1 group sample sizes: 3 years = 11, 4 years = 31, 5 years = 35, 6 years = 30, 7 years = 16, and 8 years = 17. Unaffected sibling group sample sizes: 3 years = 2, 4 years = 17, 5 years = 13, 6 years = 13, 7 years = 10, and 8 years = 8.