The c.429_452 duplication of the ARX gene: a unique developmental-model of limb kinetic apraxia:

BACKGROUND: The c.429_452dup24 of the ARX gene is a rare genetic anomaly, leading to X-Linked Intellectual Disability without brain malformation. While in certain cases c.429_452dup24 has been associated with specific clinical patterns such as Partington syndrome, the consequence of this mutation has been also often classified as "non-specific Intellectual Disability". The present work aims at a more precise description of the clinical features linked to the c.429_452dup24 mutation. METHODS: We clinically reviewed all affected patients identified in France over a five-year period, i.e. 27 patients from 12 different families. Detailed cognitive, behavioural, and motor evaluation, as well as standardized videotaped assessments of oro-lingual and gestural praxis, were performed. In a sub-group of 13 ARX patients, kinematic and MRI studies were further accomplished to better characterize the motor impairment prevalent in the ARX patients group. To ensure that data were specific to the ARX gene mutation and did not result from low-cognitive functioning per se, a group of 27 age- and IQ-matched Down syndrome patients served as control. RESULTS: Neuropsychological and motor assessment indicated that the c.429_452dup24 mutation constitutes a recognizable clinical syndrome: ARX patients exhibiting Intellectual Disability, without primary motor impairment, but with a very specific upper limb distal motor apraxia associated with a pathognomonic hand-grip. Patients affected with the so-called Partington syndrome, which involves major hand dystonia and orolingual apraxia, exhibit the most severe symptoms of the disorder. The particular "reach and grip" impairment which was observed in all ARX patients, but not in Down syndrome patients, was further characterized by the kinematic data: (i) loss of preference for the index finger when gripping an object, (ii) major impairment of fourth finger deftness, and (iii) a lack of pronation movements. This lack of distal movement coordination exhibited by ARX patients is associated with the loss of independent digital dexterity and is similar to the distortion of individual finger movements and posture observed in Limb Kinetic Apraxia. CONCLUSION: These findings suggest that the ARX c.429_452dup24 mutation may be a developmental model for Limb Kinetic Apraxia

New insight in ARX-mutated patients' language specific impairment and underlying FOXP1 dysregulation

Numéro spécial Abstracts of EPNS 2017 - 12th European Paediatric Neurology Society CongressLyon, France20- 24 June 2017 12th European Paediatric Neurology Society Congress, 20 - 24 June 2017International audienceObjective: The ARX (Aristaless Related homeoboX) gene encodes a transcription factor which mutations have been associated with syndromes ranging from severe neuronal migration defects such as lissencephaly, to mild or moderate forms of X-linked Intellectual Disability (ID) without apparent brain abnormalities. The most frequent ARX mutation (c.429_452dup24), a duplication of 24 base pairs, constitutes a recognizable clinical syndrome with ARX patients exhibiting ID, without primary motor impairment, but with a very specific upper limb distal motor apraxia associated with a pathognomonic hand-grip. Furthermore, patients also exhibit language impairment and an obvious difficulty to execute oro-lingual praxis. The aim of the present study was to better characterize language abnormalities in ARX c.429_452dup24 patients. Methods: We collected data on 16 French ARX patients, and 16 age- and IQ-matched controls (Fragile X (FraX) patients). Given the similarities between ARX mutated patients and FOXP2-mutated patients, we investigated the molecular relationship between Arx and Foxp2. Results: ARX patients have structural language impairments in both receptive and expressive aspects of language compared to FraX patients: phonetic feature recognition, receptive (ECOSSE test for sentence comprehension) and expressive (TCG-R for sentence production) morphosyntactic skills and oro-lingual dyspraxia (movements of the face, tongue, and lips) were significantly more impaired in ARX patients. FraX patients made words more complex and they were less impaired in their ability to articulate words. On the contrary, language pragmatic analysis showed that ARXdup24 patients had significantly better interactional skills than FraX. patients. Interestingly, we found that although Arx has no effect on Foxp2 expression, Arx was found to activate Foxp1 expression, and that the c.429_452dup24 mutation alters the expression of this gene. Foxp1 is known to heterodimerize with Foxp2 and has been involved in language defects. Conclusion: These data uncover a novel role of ARX in language development, probably through the regulation of Foxp1