Walking Mechanics and Movement Pattern Variability in Monozygotic Twins with Autism Spectrum Disorder

Abstract

The study of monozygotic (MZ) twins enables researchers to understand the inheritability and manifestation of many disorders due to the presence of near identical genotypes. It is reasonable to speculate that the heterogeneous manifestations of Autism Spectrum Disorder (ASD) present unique movement challenges to each MZ twin, regardless of nearly identical genotypes. However, such a study has yet to be performed. Additionally, no study has attempted to quantify the movement dysfunctions previously observed in this population. The purpose of this investigation was to examine gait parameters and movement pattern variability within one pair of monozygotic (MZ) twins diagnosed with ASD. One nine-year old pair of MZ twins with clinical diagnoses of ASD walked over-ground while kinetic and kinematic gait parameters were obtained. Point-by-point statistical and effect size (ES) analyses were performed throughout the gait cycle between twins. Movement pattern variability was quantified to explain the mechanical differences observed. Significant, (α < 0.05) and clinically meaningful (ES < 0.79) differences were observed for ground reaction forces (GRF) in vertical and horizontal axes and for sagittal plane joint positions. Unique magnitudes of joint position variability were detected in each twin. These MZ twins diagnosed with ASD exhibited different walking mechanics, reflecting the heterogeneity of ASD. Distinct walking mechanics appear related to movement pattern variability. Regardless of nearly identical genotypes, ASD appears to manifest in different walking mechanics and repeatability. These findings highlight the importance of precision medicine based treatment plans and support the reclassification of ASD as a pervasive developmental disorder.