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Résumé Chez l'enfant, les troubles de la mémoire à long-terme sont très peu identifiés et décrits dans la littérature scientifique. Ainsi, doit-on comprendre que les dysmnésies développementales ont une prévalence très faible ou bien est-ce un sous-diagnostic ? À partir d'une revue de la littérature et de deux études de cas, nous postulons que la dysmnésie développementale est un trouble du neurodéveloppement sous-diagnostiqué en raison de deux facteurs : la présence d'autres troubles du neurodéveloppement ; et l'absence de difficultés scolaires massives. La recherche systématique de troubles mnésiques chez des enfants présentant un trouble des apprentissages scolaires devrait permettre de recenser, à l'avenir, plus de dysmnésies développementales. Abstract Introduction/objective Memory disorders in adults are common after cerebral stroke, brain tumor, or major neurocognitive disorder. But in childhood, these disorders are less described in scientific literature and are perhaps less frequent. Many studies have described long-term memory disorder after hypoxic–ischemic events (see articles from Vargha-Kadhem and colleagues). This disorder is named developmental amnesia because the origin of difficulties is identified. But in a few cases (4 cases described currently) causes are unknown despite the same memory disorders. This neurodevelopmental disorder could be named: developmental dysmnesia. So, the question is: is the prevalence of developmental dysmnesia in the general population really low or is this an under-diagnosis? Temple and Richardson (2006) stated prevalence at around 5–6%, but in fact neuropsychologists never diagnose developmental dysmnesia. Method From literature review and description of two new cases which have have recently been identified (one with episodic dysmnesia and one with mixed dysmnesia), we postulate that developmental dysmnesia is an underdiagnosed neurodevelopmental disorder because of the presence of other developmental disorders such as ADHD, SLI... which become the tree that hides the forest; and because of low scholastic difficulties which are compensated for by more consequent personal effort. Conclusion Long-term memory can be perturbed in children without brain damage, which we have named developmental dysmnesia. We have demonstrated that many parameters generate few diagnostics of developmental dysmnesia which could be a neurodevelopmental disorder with the same prevalence as others. The diagnostic of memory disorder in children is difficult because complaints are not about memory, and/or scholastic difficulties are compensated. We have identified three types of developmental dysmnesia, based on the nature of the memory system that is disturbed: episodic dysmnesia, semantic dysmnesia and mixed dysmnesia (episodic and semantic memory disorders). Moreover, we could distinguish two sensorial modalities: verbal and/or visuo-spatial developmental dysmnesia. The systematic investigation of long-term memory problems in children with neurodevelopmental disorders (notably ADHD and dyslexia) must permit listing more cases of developmental dysmnesia in the future. We encourage all neuropsychologists and others professionals which working with children to assess long-term memory despite lack of complaints. [ABSTRACT FROM AUTHOR]

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]