In humans, the frequency of pathogenic alleles in cilia genes is low and a more realistic scenario is that heterozygous mutant alleles in one cilia gene may influence phenotypic expression resulting from homozygous mutations in CEP290. Heterozygous missense alleles of the AHI1 gene were identified in LCA patients with severe neurological involvement, suggesting that alleles of AHI1 may influence phenotypic expression [33]. This evidence concerns the gene AHI1 and Leber congenital amaurosis.