Objective: To investigate: 1. the diagnostic accuracy of phenotypic Early Onset Ataxia (EOA) recognition among other pediatric disorders with impaired coordination (developmental coordination disorder (DCD) and Hypotonia and/or Hypoactive Muscle activation (abbreviated as HHM), and 2. the effect of standardized instructions for EOA recognition on the phenotypic homogeneity (consensus) of assessments.

Background: Reliable phenotypic discrimination between EOA and other causes of impaired coordination is important for genetic testing, clinical surveillance and treatment (ref 2).

Methods: We included 32 children (4-17 years), diagnosed with EOA (n=11), DCD (n=10) and HHM (n=11). Three pediatric neurologists performed independent, blinded phenotypic and quantitative assessment of videotaped SARA (Scale for Assessment and Rating of Ataxia) performances. We determined inter-observer agreement and phenotypic homogeneity (i.e. the % of unanimous agreement between all 3 assessors, in line with the underlying diagnosis) and compared SARA (sub)scores between in-homogeneously assessed phenotypes. Subsequently, we evaluated the effect of standardized EOA instructions (substantiated by previous research) on phenotypic homogeneity.

Results: Inter-observer agreement (ICC) of phenotypic EOA assessment was 0.81 (very strong; p<.001). EOA was phenotypically homogeneously discerned from HHM in 100% and from DCD in 76% of the cases. In-homogeneously discerned EOA and DCD phenotypes revealed overlapping SARA scores approximating scores in the upper and lower quartile of the other group. After re-assessment with standardized EOA instructions, homogeneity increased from 76% to 89% (p<0.01).

Conclusions: The EOA phenotype can be reliably discerned from other causes of coordination impairment, but not always in a homogeneous way (i.e. incomplete consensus). In-homogeneously discerned EOA and DCD phenotypes showed overlapping SARA-scores. Re-assessment by standardized EOA instructions enhanced phenotypic homogeneity, but, before clinical application it is advisory to await further insight in these instructions, first.

References: ref 1: Sanger TD, Chen D, Delgado MR, et al. Definition and classification of negative motor signs in childhood. Pediatrics. 2006;118(5):2159-2167. ref 2: Lawerman TF, Brandsma R, van Geffen JT, et al. Reliability of phenotypic early-onset ataxia assessment. Dev Med Child Neurol. 2016;58(1):70-76.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/is-early-onset-ataxia-phenotypically-discernible-from-developmental-disorders-with-impaired-coordination/