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Background: Procedural learning refers to rule-based motor skill learning and storage. It involves the cerebellum, striatum and motor areas of the frontal lobe network. Fragile X syndrome, which has been linked with anatomical abnormalities within the striatum, may result in implicit procedural learning deficit. Methods: To address this issue, a serial reaction time (RT) task including six blocks of trials was performed by 14 individuals with fragile X syndrome, 12 individuals with Down syndrome and 12 mental age-matched control subjects. The first (B1) and fifth (B5) blocks were random whereas the others (B2, B3, B4 and B6) consisted of a repeated 10-step sequence. Results were analysed by Kruskal-Wallis one-way analysis of variance and Wilcoxon signed-rank test. Results: For patients with fragile X syndrome, the RT was highly suggestive of preserved implicit learning as a significant difference was observed between blocks B5 and B6 (P = 0.009). However, the difference of RT between B4 and B5 did not reach significance, possibly due to a subgroup of individuals who did not learn. In contrast, in the Down syndrome group, RT decreased significantly between B4 and B5 (W = 2; P = 0.003) but not between the last ordered block (B6) and the last random block (B5), suggesting a weakness in procedural learning which was sensitive to the interfering random block. Conclusion: Implicit learning is variable in genetic syndromes and therefore relatively independent of general intellectual capacities. The results are discussed together with previous reports.

Abstract: X-linked mental retardation includes more than 200 rare diseases. Fragile X mental retardation prevalence is 1/4000 to 1/9000 among boys and 1/7000 to 1/15,000 among girls. Other aetiologies are rare, but under-diagnosed and/or recently discovered. Lyon reference centre''s missions are to improve diagnosis access and quality of care, professional''s formation, patient and family information and research. When pathogenic genetic change on X chromosome is described at a boy presenting a mental retardation, genetic testing is required in his mother. When this boy has sisters, three situations arise: for symptomatic girls, it''s one step in diagnostic; for asymptomatic adult girls, molecular diagnosis takes significance in a project of access to the parenthood; for asymptomatic under 18-year-old girls, request for test is formulated by parents and raises great ethical and psychological stakes. After short recall of the clinical expression of fragile X in girls and the French legislation framing the regulation of a presymptomatic genetic testing, we will discuss these stakes starting from a case report. We will show the interest of multidisciplinary dialogue between neuropaediatrician, geneticist and child psychiatrist. Indeed, genetic testing makes it possible to specify the risk of mental retardation, but predicts neither the gravity of the handicap of the future adult in term of autonomy nor the quality of life and self-esteem, which depends on affective and educative environment. [Copyright &y& Elsevier]