TTC14 dysfunction contributing to microcephaly and lissencephaly spectrum features through protein mislocalization and impaired RNA processing.

The homozygous p.His30Arg missense variant in TTC14 destabilises the protein and mislocalises it from the nucleus to the cytosol, where it forms aggregates, with presumed impairment of RNA metabolism during brain development.

Congenital microcephaly and lissencephaly spectrum disorders are characterised by disrupted neuronal proliferation and migration, often driven by underlying genetic variants. The authors describe a homozygous missense variant in TTC14 (c.89A>G; p.His30Arg), rare and inherited from both asymptomatic parents, identified by trio exome sequencing in a female proband with microcephaly, epileptic spasms, global developmental delay, a simplified gyral pattern, focal pachygyria and corpus callosum thinning. Structural modelling places His30 at the start of an evolutionarily conserved α-helical region, and the substitution causes steric clashes, disrupted local folding and, on molecular dynamics, destabilisation with increased conformational flexibility. mRNA and protein levels remain unaltered, but the mutant protein mislocalises from the nucleus to the cytosol where it forms aggregates, and proband fibroblasts show increased cell death and altered cell cycle progression. As TTC14 interacts with RNA splicing and mRNA processing proteins, the authors propose it as a likely pathogenic candidate gene in cortical malformation syndromes.

Synthesis written by Geno'X. For the full original abstract, please refer to the source publication.

The molecular characterisation is careful, but it rests on a single patient and a single variant: as it stands, gene-disease validity for TTC14 remains limited and a homozygous variant in this gene should not be reported as diagnostic. The weak point is the absence of a rescue experiment — mislocalisation and cell death are observed, never corrected by re-expression of the wild-type protein — and a large part of the structural argument relies on simulation. The useful reflex is matchmaking submission: it is a second independent patient, not another simulation, that will settle this gene.

Analysis by Dr Thibaut Benquey