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Chapter 248nature of most studies. Notably, given the large number and wide spectrum of genetically and clinically heterogenous disorders, the absence of a perfect classification system that would prevent any inconsistency in inclusion/exclusion of reports, and differences in availability of information among genetic neurodevelopmental disorders, we cannot rule out the possibility of some inconsistencies in inclusion/exclusion of reports. Also, on the one hand, because non-English reports, studies lacking detailed information on the genetic disorder and/or criteria for parkinsonism, and studies reporting on genetic conditions with less than three reported cases, were excluded, this review may not have captured all relevant publications. On the other hand, as we included all conditions listed in HPO as “neurodevelopmental abnormality”, we may have included conditions that should not be considered to affect brain development. Heterogeneity in reporting made summarization of results difficult, hampering comparability between GND phenotypic characteristics. For example, the percentages depicted in the heat map color scheme were based on the availability of data, that greatly varied from one report to the other (Figure 1 and Supplementary Figure S2). Publication bias will have influenced the findings. Variable strength of the evidence linking genes to phenotypes and the preliminary nature of some findings should be taken into account.ConclusionParkinsonism has been reported in many GNDs. Findings from this study may provide clues for further research and improve management of patients with GNDs and/or parkinsonism.AcknowledgementAgnies van Eeghen is member of ERN-ITHACA.Funding This work was supported financially by Stichting Wetenschappelijk Onderzoek, ‘s Heeren Loo (#2210100). The funder had no role in the design and conduct of the study, preparation of the review, or approval of the manuscript.