Clinical and cellular features in patients with primary autosomal recessive microcephaly and a novel CDK5RAP2
Lina Issa1, Katrin Mueller, Katja Seufert
1Institute of Cell Biology and Neurobiology, Charité University Medicine, Berlin, Germany.
Background:
Primary autosomal recessive microcephaly (MCPH) is a rare neurodevelopmental disorder that results in severe microcephaly at birth with pronounced reduction in brain volume, particularly of the neocortex, simplified cortical gyration and intellectual disability. Homozygous mutations in the Cyclin-dependent kinase 5 regulatory subunit-associated protein 2 gene CDK5RAP2 are the cause of MCPH3. Despite considerable interest in MCPH as a model disorder for brain development, the underlying pathomechanism has not been definitively established and only four pedigrees with three CDK5RAP2 mutations have been reported. Specifically for MCPH3, no detailed radiological or histological descriptions exist.
Methods/Results:
We sought to characterize the clinical and radiological features and pathological cellular processes that contribute to the human MCPH3 phenotype. Haplotype analysis using microsatellite markers around the MCPH1-7 and PNKP loci in an Italian family with two sons with primary microcephaly, revealed possible linkage to the MCPH3 locus. Sequencing of the coding exons and exon/intron splice junctions of the CDK5RAP2 gene identified homozygosity for the novel nonsense mutation, c.4441C > T (p.Arg1481*), in both affected sons. cMRI showed microcephaly, simplified gyral pattern and hypogenesis of the corpus callosum. The cellular phenotype was assessed in EBV-transformed lymphocyte cell lines established from the two affected sons and compared with healthy male controls. CDK5RAP2 protein levels were below detection level in immortalized lymphocytes from the patients. Moreover, mitotic spindle defects and disrupted γ-tubulin localization to the centrosome were apparent.
Conclusion:
These results suggest that spindle defects and a disruption of centrosome integrity play an important role in the development of microcephaly in MCPH3.
Insights
Primary autosomal recessive microcephaly (MCPH3) is caused by CDK5RAP2 mutations. This study reveals that spindle defects and centrosome disruption contribute to microcephaly in MCPH3 patients.
Area of Science:
- Neuroscience
- Genetics
- Developmental Biology
Background:
- Primary autosomal recessive microcephaly (MCPH) is a rare neurodevelopmental disorder characterized by severe microcephaly, simplified cortical gyration, and intellectual disability.
- MCPH3 is caused by homozygous mutations in the CDK5RAP2 gene, but its underlying pathomechanism remains unclear, with limited reported cases and no detailed radiological or histological descriptions.
Purpose of the Study:
- To characterize the clinical, radiological, and cellular features of MCPH3.
- To investigate the pathomechanism underlying MCPH3 caused by CDK5RAP2 mutations.
Main Methods:
- Haplotype analysis and gene sequencing (CDK5RAP2) in an Italian family with two affected sons.
- Cerebral magnetic resonance imaging (cMRI) to assess brain structure.
- Analysis of EBV-transformed lymphocyte cell lines to evaluate CDK5RAP2 protein levels, mitotic spindle, and centrosome integrity.
Main Results:
- Identified homozygosity for a novel nonsense mutation (c.4441C>T, p.Arg1481*) in CDK5RAP2 in affected individuals.
- cMRI revealed microcephaly, simplified gyral pattern, and hypogenesis of the corpus callosum.
- Patients exhibited undetectable CDK5RAP2 protein, mitotic spindle defects, and disrupted γ-tubulin localization to the centrosome.
Conclusions:
- The findings suggest that CDK5RAP2 mutations lead to severe microcephaly in MCPH3.
- Spindle defects and compromised centrosome integrity are critical factors in the pathogenesis of MCPH3.
