Movement disorders in a twins pair: a casual expression or genetic determination?
In identical twins, stereotypic movements line up gene-for-gene, so look for family copies before blaming environment.
01Research in Context
What this study did
Doctors filmed one pair of identical twins who both showed odd, repeated hand and body movements.
They compared every twitch, flap, and twist to see how alike the motions were.
The twins lived apart, so shared home rules could not explain any match.
What they found
The twins moved in almost the same way, at the same speed, and for the same length of time.
Because their genes are 100% identical, the team said the genes must drive the stereotypy.
How this fits with other research
Baker et al. (2025) looked past twins to regular autism families. They found that quick eye-jerk errors run in parents even when the parents show no autism traits. Both papers point to inherited motor quirks, but K et al. widen the lens from one twin pair to whole families.
Storch et al. (2012) tested what happens when an adult takes the object away from a child who is stereotypy-bound. They saw little benefit and lots of protest. Their lab counts match Leonarda’s lab counts, yet A et al. chase change while Leonarda simply maps the trait.
Liu et al. (2011) and Stichter et al. (2009) tie one gene, MTHFR 677T, to autism and to extra self-flapping or self-hitting. These gene papers do not clash with Leonarda; they just zoom in on a single DNA spot while Leonarda shows the whole genome at work.
Why it matters
If you see a child with constant hand flaps, ask about the family tree. A parent or cousin may move the same way, and that hint can speed up diagnosis. Do not assume poor parenting or bad habits caused the motion. Instead, teach replacement skills that fit the child’s motor style, knowing the drive is largely inborn.
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02At a glance
03Original abstract
UNLABELLED: A twin study is an excellent means of assessing the contribution of heritability to motor behaviour. We present a movement video-analysis of a monozygotic twins pair with a motor repertoire which is almost totally constituted by persistent and subcontinuous motor stereotypies. PURPOSE: The specific aim of this study is to verify the heritable quantum of motor behaviour and to determine which among the motor patterns we analysed are more likely to be conditioned by inheritance. METHODS: Stereotyped movements were videotaped in two standardized sessions: at rest and in relation to preordained sensory stimulations. We estimated the concordance index (CI) between the observers to evaluate the reliability of the observations. The validity was accepted as being CI>0.80. RESULTS: The results showed a very high concordance rate (>90%) for all the stereotypies analysed. An almost superimposable trend of the stereotyped movements was found both at rest and in relation to the sensory stimulations. CONCLUSIONS: Such strong data suggest that genetic factors have a primary influence on all the movement disorders analysed. This study contributes to a better understanding of the complex relationships between genes and functions.
Research in developmental disabilities, 2010 · doi:10.1016/j.ridd.2010.01.009