Unsuspected consequences of synonymous and missense variants inOCA2can be detected in blood cell RNA samples of patients with albinism

ABSTRACT Oculocutaneous albinism type 2 (OCA2) is the second most frequent form of albinism and represents about 30% of OCA worldwide. As with all types of OCA, patients present with hypopigmentation of hair and skin as well as severe visual abnormalities. We focused on a subgroup of 29 patients for whom genetic diagnosis was pending because at least one of their identified variants in or around exon 10 of OCA2 is of uncertain significance (VUS). By minigene assay, we investigated the effect of these VUS on exon 10 skipping and showed that not only intronic but also some synonymous variants can result in enhanced exon skipping. We further found that excessive skipping of exon 10 could be detected directly on blood samples of patients and of their one parent with the causal variant, avoiding invasive skin biopsies. Moreover, we show that variants which result in lack of detectable OCA2 mRNA can be identified from blood samples as well, as shown for the most common OCA2 pathogenic missense variant c.1327G>A/p.(Val443Ile). In conclusion, blood cell RNA analysis allows testing the potential effect of any OCA2 VUS on transcription products. This should help to elucidate yet unsolved OCA2 patients and improve genetic counseling. SIGNIFICANCE Our study allows us to reconsider variants of unknown significance of OCA2 as pathogenic as they induce exon 10 skipping. We show that mis-splicing as well as other types of transcripts imbalance can be detected directly from blood cell samples, avoiding invasive biopsies. We recommend systematic collection of a blood RNA sample from patients with inconclusive genetic diagnosis and suspected OCA2 (e.g., only one pathogenic variant in OCA2 ; 1 VUS; 2 VUS in trans ).