Delineating the phenotype of RNU4ATAC-related spliceosomopathy.

Biallelic pathogenic variants in RNU4ATAC cause microcephalic osteodysplastic primordial dwarfism type I (MOPD1), Roifman syndrome (RS) and Lowry-Wood syndrome (LWS). These conditions demonstrate significant phenotypic heterogeneity yet have overlapping features. Although historically described as discrete conditions they appear to represent a phenotypic spectrum with clinical features not always aligning with diagnostic categories. Clinical variability and ambiguity in diagnostic criteria exist among each disorder. Here we report an individual with a novel genotype and phenotype spanning all three disorders, expanding the phenotypic spectrum of RNU4ATAC-related spliceosomeopathies.

A Polynucleotide Repeat Expansion Causing Temperature-Sensitivity Persists in Wild Irish Accessions of Arabidopsis thaliana.

Triplet repeat expansions underlie several human genetic diseases such as Huntington's disease and Friedreich's ataxia. Although such mutations are primarily known from humans, a triplet expansion associated genetic defect has also been reported at the IIL1 locus in the Bur-0 accession of the model plant Arabidopsis thaliana. The IIL1 triplet expansion is an example of cryptic genetic variation as its phenotypic effects are seen only under genetic or environmental perturbation, with high temperatures resulting in a growth defect. Here we demonstrate that the IIL1 triplet expansion associated growth defect is not a general stress response and is specific to particular environmental perturbations. We also confirm and map genetic modifiers that suppress the effect of IIL1 triplet repeat expansion. By collecting and analyzing accessions from the island of Ireland, we recover the repeat expansion in wild populations suggesting that the repeat expansion has persisted at least 60 years in Ireland. Through genome-wide genotyping, we show that the repeat expansion is present in diverse Irish populations. Our findings indicate that even deleterious alleles can persist in populations if their effect is conditional. Our study demonstrates that analysis of groups of wild populations is a powerful tool for understanding the dynamics of cryptic genetic variation.