Intellectual disability - microarray and sequencing
Gene: TAF1C Amber List (moderate evidence)I don't know
Knuutinen et al (2020 - PMID: 32779182) report on 2 individuals from 2 consanguineous families, homozygous for TAF1C missense variants.
Both presented with an early onset neurological phenotype with severe global DD, ID (2/2 - moderate and profound), spasticity (2/2), ophthalmic findings (strabismus 2/2, nystagmus 1/2). Epilepsy, abnormal brain MRI (cerebral and cerebellar atrophy and white matter hyperintensities) as well and additional findings were reported in one (always the same individual).
Following a normal CMA, exome in the first case revealed a homozygous missense SNV (NM_005679.3:c.1165C>T / p.Arg389Cys) supported by in silico predictions. mRNA and protein levels were substantially reduced in fibroblasts from this subject. Only the patient and parents were tested for the variant but not 3 unaffected sibs (fig1).
The second individual was homozygous for another missense variant (p.Arg405Cys) also supported by in silico predictions. The girl was the single affected person within the family with an unaffected sib and parents heterozygous for the variant. Several other unaffected relatives in the extended pedigree were either carriers for this variant or homozygous for the wt allele.
TAF1C encodes the TATA-box binding protein associated factor (TAF) RNA polymerase I subunit.
RNA polymerase I (Pol I) transcribes genes to produce rRNA. For Pol I to initiate transcription, two transcription factors are required : UBF (upstream binding factor encoded by UBTF) and SL1 (selectivity factor 1). The latter is formed by TBP (TATA-binding protein) and 3 Pol I-specific TBP-associated factors (TAFs).
A recurrent de novo missense variant in UBTF (encoding the other Pol I transcription factor) causes a disorder with highly similar features. The specific variant acts through a gain-of-function mechanism (and not by LoF which appears to apply for TAF1C based on expression data).
The authors hypothesize that altered Pol I activity and resulting ribosomal stress could cause the microcephaly and leukodystrophy (both reported in 1 - the same - individual).
As a result, TAF1C may be considered for inclusion in the ID panel with amber rating pending further evidence.
Sources: LiteratureCreated: 18 Aug 2020, 12:38 a.m.
Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal
Phenotypes
Global developmental delay; Intellectual disability; Spasticity; Strabismus; Seizures; Abnormality of nervous system morphology
Publications
Gene: taf1c has been classified as Amber List (Moderate Evidence).
gene: TAF1C was added gene: TAF1C was added to Intellectual disability. Sources: Literature Mode of inheritance for gene: TAF1C was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: TAF1C were set to 32779182 Phenotypes for gene: TAF1C were set to Global developmental delay; Intellectual disability; Spasticity; Strabismus; Seizures; Abnormality of nervous system morphology Penetrance for gene: TAF1C were set to Complete Review for gene: TAF1C was set to AMBER
If promoting or demoting a gene, please provide comments to justify a decision to move it.
Genes included in a Genomics England gene panel for a rare disease category (green list) should fit the criteria A-E outlined below.
These guidelines were developed as a combination of the ClinGen DEFINITIVE evidence for a causal role of the gene in the disease(a), and the Developmental Disorder Genotype-Phenotype (DDG2P) CONFIRMED DD Gene evidence level(b) (please see the original references provided below for full details). These help provide a guideline for expert reviewers when assessing whether a gene should be on the green or the red list of a panel.
A. There are plausible disease-causing mutations(i) within, affecting or encompassing an interpretable functional region(ii) of this gene identified in multiple (>3) unrelated cases/families with the phenotype(iii).
OR
B. There are plausible disease-causing mutations(i) within, affecting or encompassing cis-regulatory elements convincingly affecting the expression of a single gene identified in multiple (>3) unrelated cases/families with the phenotype(iii).
OR
C. As definitions A or B but in 2 or 3 unrelated cases/families with the phenotype, with the addition of convincing bioinformatic or functional evidence of causation e.g. known inborn error of metabolism with mutation in orthologous gene which is known to have the relevant deficient enzymatic activity in other species; existence of an animal model which recapitulates the human phenotype.
AND
D. Evidence indicates that disease-causing mutations follow a Mendelian pattern of causation appropriate for reporting in a diagnostic setting(iv).
AND
E. No convincing evidence exists or has emerged that contradicts the role of the gene in the specified phenotype.
(i)Plausible disease-causing mutations: Recurrent de novo mutations convincingly affecting gene function. Rare, fully-penetrant mutations - relevant genotype never, or very rarely, seen in controls. (ii) Interpretable functional region: ORF in protein coding genes miRNA stem or loop. (iii) Phenotype: the rare disease category, as described in the eligibility statement. (iv) Intermediate penetrance genes should not be included.
It’s assumed that loss-of-function variants in this gene can cause the disease/phenotype unless an exception to this rule is known. We would like to collect information regarding exceptions. An example exception is the PCSK9 gene, where loss-of-function variants are not relevant for a hypercholesterolemia phenotype as they are associated with increased LDL-cholesterol uptake via LDLR (PMID: 25911073).
If a curated set of known-pathogenic variants is available for this gene-phenotype, please contact us at [email protected]
We classify loss-of-function variants as those with the following Sequence Ontology (SO) terms:
Term descriptions can be found on the PanelApp homepage and Ensembl.
If you are submitting this evaluation on behalf of a clinical laboratory please indicate whether you report variants in this gene as part of your current diagnostic practice by checking the box
Standardised terms were used to represent the gene-disease mode of inheritance, and were mapped to commonly used terms from the different sources. Below each of the terms is described, along with the equivalent commonly-used terms.
A variant on one allele of this gene can cause the disease, and imprinting has not been implicated.
A variant on the paternally-inherited allele of this gene can cause the disease, if the alternate allele is imprinted (function muted).
A variant on the maternally-inherited allele of this gene can cause the disease, if the alternate allele is imprinted (function muted).
A variant on one allele of this gene can cause the disease. This is the default used for autosomal dominant mode of inheritance where no knowledge of the imprinting status of the gene required to cause the disease is known. Mapped to the following commonly used terms from different sources: autosomal dominant, dominant, AD, DOMINANT.
A variant on both alleles of this gene is required to cause the disease. Mapped to the following commonly used terms from different sources: autosomal recessive, recessive, AR, RECESSIVE.
The disease can be caused by a variant on one or both alleles of this gene. Mapped to the following commonly used terms from different sources: autosomal recessive or autosomal dominant, recessive or dominant, AR/AD, AD/AR, DOMINANT/RECESSIVE, RECESSIVE/DOMINANT.
A variant on one allele of this gene can cause the disease, however a variant on both alleles of this gene can result in a more severe form of the disease/phenotype.
A variant in this gene can cause the disease in males as they have one X-chromosome allele, whereas a variant on both X-chromosome alleles is required to cause the disease in females. Mapped to the following commonly used term from different sources: X-linked recessive.
A variant in this gene can cause the disease in males as they have one X-chromosome allele. A variant on one allele of this gene may also cause the disease in females, though the disease/phenotype may be less severe and may have a later-onset than is seen in males. X-linked inactivation and mosaicism in different tissues complicate whether a female presents with the disease, and can change over their lifetime. This term is the default setting used for X-linked genes, where it is not known definitately whether females require a variant on each allele of this gene in order to be affected. Mapped to the following commonly used terms from different sources: X-linked dominant, x-linked, X-LINKED, X-linked.
The gene is in the mitochondrial genome and variants within this can cause this disease, maternally inherited. Mapped to the following commonly used term from different sources: Mitochondrial.
Mapped to the following commonly used terms from different sources: Unknown, NA, information not provided.
For example, if the mode of inheritance is digenic, please indicate this in the comments and which other gene is involved.