Not Just Loss-of-Function Variations: Identification of a Hypermorphic Variant in a Patient With a CDKL5 Missense...

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• CDKL5 deficiency disorder (CDD) is a severe neurodevelopmental condition linked to the X-linked CDKL5 gene.
• Pathogenic variants typically affect the N-terminal catalytic domain, impacting brain development.
• The consequences of increased CDKL5 activity, unlike loss-of-function, are not well understood.

Purpose of the Study:

• To investigate the molecular consequences of a novel CDKL5 variant, p.(Thr958Arg), identified in a patient with mild epilepsy.
• To understand the impact of this variant on CDKL5 kinase activity and subcellular localization.
• To contribute to the comprehension of genetic variations in CDKL5-associated neurological disorders.

Main Methods:

• Utilized MRI and video EEG telemetry for clinical assessment.
• Employed Bayley III scales for developmental evaluation.
• Conducted molecular analyses including RT-PCR, Western blotting, and immunofluorescence to characterize the variant's effects on mRNA, protein stability, kinase activity, and localization.

Main Results:

• The identified c.2873C>G substitution resulted in the p.(Thr958Arg) variant, leading to significantly increased CDKL5 autophosphorylation and enhanced phosphorylation of its target MAP1S.
• This hyperactivation of CDKL5 occurred without apparent changes in its subcellular distribution.
• The patient exhibited a skewed X chromosome inactivation pattern favoring the variant allele.

Conclusions:

• The c.2873C>G nucleotide substitution represents a pathogenic, hypermorphic variation of the CDKL5 gene.
• This study underscores the necessity of precise control over CDKL5 enzymatic activity for normal brain function.
• The findings expand the understanding of genotype-phenotype correlations in CDKL5-related disorders.