NeuroImage: Clinical (Jan 2018)

Basal ganglia involvement in ARX patients: The reason for ARX patients very specific grasping?

  • Aurore Curie,
  • Gaëlle Friocourt,
  • Vincent des Portes,
  • Alice Roy,
  • Tatjana Nazir,
  • Amandine Brun,
  • Anne Cheylus,
  • Pascale Marcorelles,
  • Kalliroi Retzepi,
  • Nasim Maleki,
  • Gérald Bussy,
  • Yves Paulignan,
  • Anne Reboul,
  • Danielle Ibarrola,
  • Jian Kong,
  • Nouchine Hadjikhani,
  • Annie Laquerrière,
  • Randy L. Gollub

Journal volume & issue
Vol. 19
pp. 454 – 465

Abstract

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The ARX (Aristaless Related homeoboX) gene was identified in 2002 as responsible for XLAG syndrome, a lissencephaly characterized by an almost complete absence of cortical GABAergic interneurons, and for milder forms of X-linked Intellectual Disability (ID) without apparent brain abnormalities. The most frequent mutation found in the ARX gene, a duplication of 24 base pairs (c.429_452dup24) in exon 2, results in a recognizable syndrome in which patients present ID without primary motor impairment, but with a very specific upper limb distal motor apraxia associated with a pathognomonic hand-grip, described as developmental Limb Kinetic Apraxia (LKA).In this study, we first present ARX expression during human fetal brain development showing that it is strongly expressed in GABAergic neuronal progenitors during the second and third trimester of pregnancy. We show that although ARX expression strongly decreases towards the end of gestation, it is still present after birth in some neurons of the basal ganglia, thalamus and cerebral cortex, suggesting that ARX also plays a role in more mature neuron functioning. Then, using morphometric brain MRI in 13 ARX patients carrying c.429_452dup24 mutation and in 13 sex- and age-matched healthy controls, we show that ARX patients have a significantly decreased volume of several brain structures including the striatum (and more specifically the caudate nucleus), hippocampus and thalamus as well as decreased precentral gyrus cortical thickness. We observe a significant correlation between caudate nucleus volume reduction and motor impairment severity quantified by kinematic parameter of precision grip.As basal ganglia are known to regulate sensorimotor processing and are involved in the control of precision gripping, the combined decrease in cortical thickness of primary motor cortex and basal ganglia volume in ARX dup24 patients is very likely the anatomical substrate of this developmental form of LKA. Keywords: ARX, Human brain development, Intellectual disability, Morphometric MRI, Kinematic, Limb Kinetic Apraxia