article · Human Mutation
TAF1/MRXS33 intellectual disability syndrome is a neurodevelopmental condition caused by pathogenic variants in the X-linked gene TAF1, which is involved in RNA polymerase II transcription. While early reports linked the condition to hypotonia, facial dysmorphia, and developmental delay leading to intellectual disability or autism spectrum disorder, examination of 27 newly identified families significantly widens this spectrum. Using a genotype-first approach, familial segregation analysis, bioinformatics, molecular modelling, and phenotypic clustering across 51 Human Phenotype Ontology terms, the variants were evaluated for pathogenicity. The resulting clinical presentations show substantial pleiotropy and variability. Newly documented features include brain morphological abnormalities, seizures, hearing loss, and heart malformations. The broadened allelic series illustrates the persistent difficulties of classifying inherited missense variants on the X chromosome.
Identifying the genetic causes of rare neurodevelopmental disorders is critical for securing accurate diagnoses for affected individuals and their families. Broadening the symptoms linked to TAF1, such as heart defects and seizures, helps healthcare providers recognise the condition earlier. Defining these genetic profiles also aids clinical geneticists in interpreting complex genetic test results and delivering more reliable counselling for inherited X-linked conditions.
This early-stage clinical research could inform molecular diagnostics companies, clinical geneticists, and software providers developing variant interpretation pipelines. Incorporating the expanded TAF1 variant catalogue and associated phenotypic terms into diagnostic gene panels can improve the classification accuracy of rare disease tests. Any practical adoption remains at the level of diagnostic knowledge integration, as the findings support clinical test design and reporting rather than standalone therapeutics or devices.
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We recently described a new neurodevelopmental syndrome (TAF1/MRXS33 intellectual disability syndrome) (MIM# 300966) caused by pathogenic variants involving the X-linked gene TAF1, which participates in RNA polymerase II transcription. The initial study reported eleven families, and the syndrome was defined as presenting early in life with hypotonia, facial dysmorphia, and developmental delay that evolved into intellectual disability (ID) and/or autism spectrum disorder (ASD). We have now identified an additional 27 families through a genotype-first approach. Familial segregation analysis, clinical phenotyping, and bioinformatics were capitalized on to assess potential variant pathogenicity, and molecular modelling was performed for those variants falling within structurally characterized domains of TAF1. A novel phenotypic clustering approach was also applied, in which the phenotypes of affected individuals were classified using 51 standardized Human Phenotype Ontology (HPO) terms. Phenotypes associated with TAF1 variants show considerable pleiotropy and clinical variability, but prominent among previously unreported effects were brain morphological abnormalities, seizures, hearing loss, and heart malformations. Our allelic series broadens the phenotypic spectrum of TAF1/MRXS33 intellectual disability syndrome and the range of TAF1 molecular defects in humans. It also illustrates the challenges for determining the pathogenicity of inherited missense variants, particularly for genes mapping to chromosome X. This article is protected by copyright. All rights reserved.
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DOI: 10.1002/humu.23936
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