Common causes of ISs were excluded by brain magnetic resonance imaging (MRI), metabolic screening, array-comparative genomic hybridization (CGH) and testing for mutations in CDKL5, STXBP1, and for ARX duplications.
Mutations in the Aristaless-related homeobox gene (ARX) lead to a range of X-linked intellectual disability phenotypes, with truncating variants generally resulting in severe X-linked lissencephaly with ambiguous genitalia (XLAG), and polyalanine expansions and missense variants resulting in infantile spasms.
We propose a core pathway of transcription regulators, including Hdac4, involved in chromatin condensation and transcriptional repression, and one of its targets, the transcription factor Twist1, as potential drivers of the ID and infantile spasms in patients with ARX polyalanine expansion mutations.
Although null mutations of ARX in human patients result in the severe neurologic syndrome XLAG (X-linked lissencephaly associated with abnormal genitalia), the most common mutation is the expansion of the first polyalanine tract of ARX, which results primarily in the clinical syndrome ISSX (infantile spasms).
Polyalanine (polyA)-expansion-encoding mutations of aristaless-related homeobox (ARX) cause a spectrum of X-linked ID (XLID) diseases and chronic epilepsy, including infantile spasms.
Aristaless-related homeobox gene (ARX) mutation leads to several neurological disorders including X-linked lissencephaly with abnormal genitalia (XLAG), West syndrome and Partington syndrome, with XLAG being the most severe form.
This combination of early infantile spasms followed by a complex movement disorder contributes further to extent the pleiotropy of the ARX-linked "interneuronopathy" and should lead the clinician to ARX mutation screening.
ARX is a crucial gene for the development of interneurons in the fetal brain, and a polyalanine expansion mutation of ARX causes mental retardation and seizures, including those of West syndrome, in males.
Mutations in the human ARX gene have been shown to cause nonsyndromic X-linked mental retardation (MRX) as well as syndromic forms such as X-linked lissencephaly with abnormal genitalia (XLAG), Partington syndrome and X-linked infantile spasm.
Lissencephaly caused by LIS1 or DCX mutation frequently results in West syndrome, while lissencephaly due to ARX mutation is associated with the most severe form of epilepsy but never results in West syndrome nor infantile spasms.
Mutations in the CDKL5 gene (also known as STK9) have recently been shown to cause early onset epilepsy and severe mental retardation (ISSX or West syndrome).
The striking epileptogenicity of X-linked lissencephaly with abnormal genitalia and West's syndrome associated with ARX mutations i s considered to be caused by a disorder of interneurons involving a tangentialmigration disorder.
Our data suggest expansions in one of the ARX polyA tracts results in nuclear protein aggregation and an increase in cell death; likely underlying the pathogenesis of the associated infantile spasms and mental retardation.
Our data suggest expansions in one of the ARX polyA tracts results in nuclear protein aggregation and an increase in cell death; likely underlying the pathogenesis of the associated infantile spasms and mental retardation.