In vivo bioassay to test the pathogenicity of missense human AIP variants

Heterozygous germline loss-of-function mutations in the aryl hydrocarbon receptor-interacting protein gene (AIP) predispose to childhood-onset pituitary tumours. The pathogenicity of missense variants may pose difficulties for genetic counselling and family follow-up.

To develop an in vivo system to test the pathogenicity of human AIP mutations using the fruit fly Drosophila melanogaster.

We generated a null mutant of the Drosophila AIP orthologue, CG1847, a gene located on the Xchromosome, which displayed lethality at larval stage in hemizygous knockout male mutants (CG1847 ). We tested human missense variants of 'unknown significance', with 'pathogenic' variants as positive control.

We found that human AIP can functionally substitute for CG1847, as heterologous overexpression of human AIP rescued male CG1847 lethality, while a truncated version of AIP did not restore viability. Flies harbouring patient-specific missense AIP variants (p.C238Y, p.I13N, p.W73R and p.G272D) failed to rescue CG1847 mutants, while seven variants (p.R16H, p.Q164R, p.E293V, p.A299V, p.R304Q, p.R314W and p.R325Q) showed rescue, supporting a non-pathogenic role for these latter variants corresponding to prevalence and clinical data.

Our in vivo model represents a valuable tool to characterise putative disease-causing human AIP variants and assist the genetic counselling and management of families carrying AIP variants.