Xq28 duplication overlapping the int22h-1/int22h-2 region and including RAB39B and CLIC2 in a family with intellectual and developmental disability

Abstract

Duplications involving terminal Xq28 are a known cause of intellectual disability (ID) in males and in females with unfavorable X-inactivation patterns. Within Xq28, functional disomy of MECP2 causes a severe ID syndrome, however the dosage sensitivity of other Xq28 duplicated genes is less certain. Duplications involving the int22h-1/int22h-2 LCR-flanked region in distal Xq28 have recently been linked to a novel ID-associated phenotype. While evidence for the dosage sensitivity of this region is emerging, the phenotypic contribution of individual genes within the int22h-1/int22h-2-flanked region has yet to be determined. We report a familial case of a novel 774 kb Xq28-qter duplication, detected by cytogenomic microarray analysis, that partially overlaps the int22h-1/int22h-2-flanked region. This duplication and a 570 kb Xpter-p22.33 loss within the pseudoautosomal region were identified in three siblings, one female and two males, who presented with developmental delays/intellectual disability, mild dysmorphic features and short stature. Although unconfirmed, these results are suggestive of maternal inheritance of a recombinant X. We compare our clinical findings to patients with int22h-1/int22h-2-mediated duplications and discuss the potential pathogenicity of genes within the duplicated region, including those within the shared region of overlap, RAB39B and CLIC2.

Keywords: CLIC2; RAB39B; Xp22.33 deletion; Xq28 duplication; int22h.