Whole-exome sequencing in familial keratoconus: the challenges of a genetically complex disorder

The underlying genetic causes of keratoconus are essentially unknown. Here, we conducted whole-exome sequencing in 2 Brazilian families with keratoconus.

Whole-exome sequencing was performed on 6 keratoconus-affected individuals of 2 unrelated pedigrees from Southern Brazil. Pathogenic variants were identified in a modified Trio analysis (1 parent and 2 children) using candidate gene filtering. All the affected subjects underwent detailed corneal tomographic evaluation. Clinically relevant variants that were present in affected individuals at minor allele frequencies <1% were examined in the 1000 Genomes Project single nucleotide polymorphism ABraOM and transcription gene (RefSeq and Ensembl) databases.

In family 1, a sequence variant in chromosome 1 (q21.3) was observed within the filaggrin gene. All the tested family members shared a heterozygous missense pathogenic variant in the c.4678C>T position. In family 2, exome analysis demonstrated a sequence variant in chromosome 16 (q24.2) within the gene encoding zinc finger protein 469 (ZNF469). Members of family 2 shared a heterozygous missense variant in the c.1489G>A position. In addition, the exomes of the 2 families were examined for shared genetic variants among all affected individuals. Filtering criteria did not identify any rare sequence variants in a single gene segregated in both families.

Our findings show that a complete genotype-phenotype correlation could not be identified, suggesting that keratoconus is a genetically heterogeneous disease. In addition, we believe that whole-exome sequencing-based segregation analysis is probably not the best strategy for identifying variants in families with isolated keratoconus.