Screening of a large Rubinstein-Taybi cohort identified many novel variants and emphasizes the importance of the CREBBP histone acetyltransferase domain.

Pathogenic variants within the CREBBP and EP300 genes account for the majority of individuals with Rubinstein-Taybi syndrome (RSTS). Data are presented from a large cohort of 395 individuals referred for diagnostic testing of CREBBP, and of the 19 CREBBP missense variants classified as likely pathogenic in this study, 17 were within the histone acetyltransferase (HAT) domain, providing evidence that this domain is critical to the normal function of the CREBBP protein (CBP). The data presented here, combined with other published results, suggest that the presence of a missense variant within the CBP HAT domain can be considered as moderate evidence of pathogenicity in the context of official variant interpretation guidelines. Within our study cohort, 129 had a pathogenic or likely pathogenic CREBBP variant and 5 had a variant of uncertain significance (VUS) which warranted familial studies. 147 of the remaining probands were also screened for EP300 and a further 16 pathogenic or likely pathogenic variants were identified, plus one VUS. Therefore, this analysis has provided a molecular diagnosis in at least 145 individuals with RSTS (37%) and identified a wide range of variants (n = 133) of which 103 were novel.

Screening of a large PAX6 cohort identified many novel variants and emphasises the importance of the paired and homeobox domains.

Pathogenic variants within PAX6 are most often associated with aniridia, but have been linked with other phenotypes such as nystagmus, cataracts and foveal hypoplasia. Data are presented from a large cohort of 434 probands referred for PAX6 diagnostic testing. This analysis identified a wide range of pathogenic variants (n = 145) in 254 probands (including 61 novel variants). Excluding missense variants predicted to affect splicing, all 29 of the remaining missense variants were located within the paired (n = 27) or homeobox (n = 2) domains of the PAX6 protein, providing further evidence that these domains are critical to normal PAX6 function. Genotype-phenotype evidence suggests that while aniridia is associated with most variant types, a much broader clinical spectrum is seen in patients harbouring a missense variant, or a frameshift or run-on variant that results in an elongated or extended PAX6 protein.