A Novel Variant c. <scp>149G</scp> &gt;A in <scp>CDK5</scp> Gene Causing Lissencephaly Type 7

Lissencephaly is a genetically heterogeneous condition caused by aberrant neuronal migration. Cerebellar hypoplasia has been commonly associated in some subtypes of lissencephaly, notably the tubulinopathies. CDK5 is a microtubule-associated protein, and its defective function has been implicated in various neurodevelopmental and neurodegenerative disorders. Biallelic loss-of-function variant in CDK5 has been reported to cause lissencephaly type 7 in a single family to date. We describe an infant with diffuse agyria, cerebellar hypoplasia, and agenesis of the corpus callosum harboring a homozygous novel missense variant c.149G>A in CDK5. She had refractory seizures, pyramidal signs, microcephaly, and growth failure. She did not achieve any developmental milestones and succumbed at 4 months of age. The disease course and severity were similar to those observed in the patients in the first report, who had a splicing defect leading to loss-of-function. In silico functional analysis showed that the variant c.149G>A (p.Arg50Gln) caused instability of the CDK5 protein structure, potentially causing functional disruption. Functional analysis of the p.Arg50Gln variant, using a yeast complementation assay, showed a deleterious impact of the variant. In conclusion, this is the second family with CDK5-related lissencephaly type 7.