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  • The variants all occurred at residues

    2021-12-07

    The 17 variants all occurred at residues conserved among vertebrates (Figure 1B) and in regions depleted in missense variants in gnomAD. Indeed, when we assessed missense tolerance ratios for TRRAP, we observed that most of the 17 variants were in regions intolerant to missense variants (Figure 2B). Nine out of the 17 variants occurred at highly mutable CpG sites, including one within the lumiracoxib that leads to the recurrent p.Ala1043Thr variant observed in five individuals. Six missense variants with lesser evidence for pathogenicity were found in another six unrelated individuals (individuals 25 to 30 in Table S1). These variants might be deleterious but were not clearly pathogenic: perhaps the inheritance pattern could not be determined; the variant was present in gnomAD or led to another missense change at the same residue as a variant reported in gnomAD; or the variant was located in a less conserved region of TRRAP (Table S2). Given the number of de novo variants identified, the enrichment for TRRAP de novo variants in our study was calculated as (p = 4.2 × 10−6) on the basis of denovolyzer. Nevertheless, the current number of 22 detected de novo variants in TRRAP is not of genome-wide significance (p = 0.08) after correction for the following: (a) ∼19,000 protein-coding genes, (b) 22,898 trios studied, and (c) the underlying mutability of the full-length protein-coding TRRAP transcript. However, this statistical calculation does not take into account the spatial distribution of the variants. Indeed, three-dimensional modeling of human TRRAP structure inferred from the orthologous Saccharomyces cerevisiae protein Tra1 (Figure 2C) suggested a clustering of the variants in different regions of TRRAP. The most important clustering was observed for 13 variants between codons 1031 and 1159. Interestingly, when visualized in 3D, these variants localized near one another (Figure 1C), revealing a domain of TRRAP with a potentially novel specific function, although this domain has not yet been characterized. We performed a statistical clustering analysis comparing the mean distance between observed variants to ten million permutations of random variants, as previously described. This analysis revealed a significant clustering of variants along the primary sequence of TRRAP (p value = 9 × 10−8), suggesting a model in which specific domains are affected and haploinsufficiency is unlikely, at least for clustering variants. Among the 24 individuals who carried pathogenic variants, 19 presented with facial dysmorphisms. Recurrent features that were noted among these individuals included upslanted palpebral fissures, epicanthus, telecanthus, a wide nasal bridge and ridge, a broad and smooth philtrum, and a thin upper lip (Figure 3). We performed a computer-assisted facial gestalt visualization,28, 29 which highlighted several of these features, particularly for individuals with variants clustering with the recurrent p.Ala1043Thr variant (Figure 3R). All the individuals had developmental delay, although the severity of intellectual disability (ID) was highly variable. Whereas most individuals had apparent ID with markedly impaired basic life functions, some of them presented with mild ID or even no cognitive deficits (Table 2 and Table S3). Peripheral neuropathy was also noted; corpus callosum was severe in one individual and consisted of lower-limb hyperreflexia in five other individuals. In addition to alteration in cerebral function, some individuals showed brain, cerebellum, heart, kidney, or urogenital malformations. We observed a strong genotype-phenotype correlation (Figure 1A, Table 2); the highest incidence of malformations was seen in 13 individuals whose variants cluster in the region of the predicted protein from codons 1031 to 1159: c.3093T>G (p.Ile1031Met), c.3104G>A (p.Arg1035Gln), c.3111C>A (p.Ser1037Arg), c.3127G>A (p.Ala1043Thr), c.3311A>G (p.Glu1104Gly), c.3316G>A (p.Glu1106Lys), c.3331G>T (p.Gly1111Trp), and c.3475G>A (p.Gly1159Arg). In contrast, individuals with variants residing outside of this region had less malformation and presented mainly with autism spectrum disorder (ASD) and/or ID, sometimes associated with epilepsy. Variants in these individuals were more dispersed along the protein, although some, including c.5575C>T (p.Arg1859Cys), c.5596T>A (p.Trp1866Arg), c.5598G>T (p.Trp1866Cys), c.5647G>A (p.Gly1883Arg), and c.5795C>T (p.Pro1932Leu), apparently aggregated in another region.