Intellectual disabilityGene: AFF3
As noted by Konstantinos Varvagiannis, Voisin et al., 2019 (not yet in PubMed) describe de novo missense variants in the degron of AFF3 (a region required for its degradation) in 10 unrelated individuals with symptoms including ID. 4 different missense variants were identified (p.A258S, p.A258T, p.A258V and p.V260G). Although there are sufficient cases with a relevant phenotype (plus the individual reported in PMID:18616733), I have rated as Amber pending publication of the Voisin 2019 article: as OMIM note in their correspondance on AFF3, information changes from the initial bioRxiv upload to peer-reviewed publication. Therefore updated rating of AFF3 from Red to Amber, added 'watchlist' tag and 'missense' tag, and will re-curate when the paper is published.
Created: 15 Aug 2019, 12:31 p.m. | Last Modified: 15 Aug 2019, 12:41 p.m.
Panel Version: 2.1004
Voisin et al. (2019 - https://doi.org/10.1101/693937) report on 10 individuals with de novo missense AFF3 variants affecting a 9-amino-acid sequence (degron) important for the protein's degradation and summarize the phenotype of an additional individual previously described by Steichen-Gersdorf et al. (2008 - PMID: 18616733) with a 500 kb deletion affecting only AFF3 (LAF4) and removing also this sequence.
The phenotype of missense variants consisted of kidney anomalies, mesomelic dysplasia, seizures, hypertrichosis, intellectual disability and pulmonary problems and was overlapping with that of the deletion. [10 of 11 subjects exhibited severe developmental epileptic encephalopathy].
9 probands harbored missense variants affecting the codon 258 while one individual had a variant affecting codon 260 [c.772G>T or p.Ala258Ser (x2), c.772G>A or p.Ala258Thr (x6), c.773C>T or p.Ala258Val (x1) and c.779T>G or p.(Val260Gly) (x1) - NM_001025108.1 / NP_001020279.1]. The deletion removed exons 4-13.
AFF1-4 are ALF transcription factor paralogs, components of the transcriptional super elongation complex regulating expression of genes involved in neurogenesis and development.
Using HEK293T cells expressing FLAG-tagged AFF3 (and AFF4) wt or mutants, accumulation of mutated forms was shown upon immunoblot.
Aff3+/- and/or -/- mice exhibit skeletal defects. These were more pronounced in homozygous mice which demonstrated also some elements in favor of kidney dysfunction and/or metabolic deregulation and possible neurological dysfunction (signs of impaired hearing and diminished grip strength). Homozygous mice had CNS anomalies (enlarged lateral ventricles and decreased corpus callosum size) similar to some affected individuals, although these were not observed in another Aff3-/- model. Knock-in mice modeling the microdeletion and the Ala258Thr variant displayed lower mesomelic limb deformities and early lethality respectively [cited PMIDs : 21677750, 25660031, knock-in model was part of the present study].
Accumulation of the protein in zebrafish (by overexpression of the human wt AFF3 mRNA), led to morphological defects.
Reanalysis of transcriptome data from previously generated HEK293T cell lines knocked down for AFF2, AFF3 and AFF4 by shRNAs (study) suggested that these transcription factors are not redundant.
Finally, CHOPS syndrome (#616368) due to mutations of AFF4 also leading to increased protein stability presents a partially overlapping phenotype (incl. cognitive impairment) to that of AFF3.
Shimizu et al. (8/2019 - PMID: 31388108) describe an additional individual with de novo AFF3 missense variant. The phenotype overlaps with that summarized by Voisin et al. incl. mesomelic dysplasia with additional skeletal anomalies, bilateral kidney hypoplasia and severe DD at the age of 2.5 years. Seizures and pulmonary problems were not observed. Although a different RefSeq is used the variant is among those also reported by Voisin et al. [NM_002285.2:c.697G>A (p.Ala233Thr) corresponding to NM_001025108.1:c.772G>A (p.Ala258Thr)].
In G2P, AFF3 is associated with Skeletal dysplasia with severe neurological disease (disease confidence : probable / ID and seizures among the assigned phenotypes). There is no associated phenotype in OMIM.
Some diagnostic laboratories include AFF3 in their ID panel (eg. among the many co-authors' affiliations GeneDx and Victorian Clinical Genetics - which was already listed as source for AFF3 in the current panel).
As a result this gene can be considered for upgrade to green (relevant phenotype and severity, sufficient cases, evidence for accumulation similar to AFF4, animal models, etc) or amber (pending publication of the article).
[Review modified to add additional reference/case report]
Created: 7 Aug 2019, 5:30 p.m. | Last Modified: 10 Dec 2019, 12:40 p.m.
Panel Version: 2.1143
Mode of inheritance
MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Intellectual disability; Seizures; Abnormality of skeletal morphology; Abnormality of the urinary system; Hypertrichosis; Abnormality of the respiratory system
Mode of pathogenicity
Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Variants in this GENE are reported as part of current diagnostic practice
Publications for gene: AFF3 were set to
Phenotypes for gene: AFF3 were changed from to Intellectual disability; Seizures
Mode of inheritance for gene: AFF3 was changed from to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Mode of pathogenicity for gene: AFF3 was changed from to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Gene: aff3 has been classified as Amber List (Moderate Evidence).
Tag watchlist tag was added to gene: AFF3.
Tag missense tag was added to gene: AFF3.
gene: AFF3 was added gene: AFF3 was added to Intellectual disability. Sources: Victorian Clinical Genetics Services Mode of inheritance for gene: AFF3 was set to