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Intellectual disability

Gene: TIAM1

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TIAM1 (T-cell lymphoma invasion and metastasis 1)
EnsemblGeneIds (GRCh38): ENSG00000156299
EnsemblGeneIds (GRCh37): ENSG00000156299
OMIM: 600687, Gene2Phenotype
TIAM1 is in 2 panels

1 review

Konstantinos Varvagiannis (Other)

I don't know

Lu et al (2022 - PMID: 35240055) describe 5 individuals (from 4 families) with biallelic TIAM1 missense variants.

The phenotype overall corresponded to a neurodevelopmental disorder with DD (5/5), ID (4/4 individuals of relevant age - 3 families), speech delay (5/5), seizures (5/5 - onset: 2m-13y) and behavioral abnormalities (2/2, sibs with autism and ADHD). Several subjects had endocrine symptoms, namely hypothyroidism (N=3 - 2 families), Addison's disease (1) or hypomagnesemia (1). Non-consistent abnormalities were reported in (3/3) subjects who had a brain MRI.

Previous investigations were mentioned for 3 individuals (incl. 2 sibs) and included normal CMA and/or metabolic workup.

Singleton or trio exome sequencing (in one family) revealed biallelic missense TIAM1 variants.

6 different missense variants were reported, all ultra-rare or not present in gnomAD (also o/e:0.2, pLI:0.96), with CADD scores in favor of deleterious effect (NM_001353694.2): c.67C>T/p.Arg23Cys*, c.2584C>T/p.Leu862Phe*, c.983G>T/p.Gly328Val*, c.4640C>A/p.Ala1547Glu, c.1144G>C/p.Gly382Arg, c.4016C>T/p.Ala1339Val.

TIAM1 encodes a RAC1-specific guanine exchange factor (GEF), regulating RAC1 signaling pathways that in turn affect cell shape, migration, adhesion, growth, survival, and polarity, and influence actin cytoskeletal organization, endocytosis, and membrane trafficking. RAC1 signaling plays important role in control of neuronal morphogenesis and neurite outgrowth (based on the summary by Entrez and authors).

TIAM1 is highly expressed in human brain (GTEx).

The authors provide evidence that sif, the Drosophila ortholog, is expressed primarily in neurons of the fly CNS (but not in glia). Using different sif LoF mutant flies they demonstrate that loss of sif impairs viability. Surviving flies exhibited climbing defects and seizure-like behaviors, both significantly rescued upon UAS-sif expression. Neuronal specific sif knockdown resulted in similar phenotypes to ubiquitous knockdown, while glial knockdown did not result in climbing defects.

The semi-lethal phenotype could be fully rescued by expression of the fly sif cDNA, but only partially by human TIAM1 cDNA reference. Upon expression, 3 patient-variants (R23C, L862F, G328V) had variable rescue abilities similar to or lower (R23C) than TIAM1 Ref. TIAM1 Ref and variants could not rescue the neurological phenotypes though. Higher/ectopic expression of sif or TIAM1 Ref was toxic, which was also observed to a lesser extent for variants.

Overall, the evidence provided suggests that the 3 variants tested induce partial LoF.

In a recent study cited (PMID: 33328293), Tiam1 KO mice had simplified dendritic arbors, reduced spine density and diminished excitatory transmission in dentate gyrus. The authors comment that this mouse model presented only subtle behavioral abnormalities which they speculate may be secondary to GEF redundancy (eg. Tiam2).

There is no TIAM1-associated phenotype in OMIM/G2P/SysID. TIAM1 is included in PanelApp Australia in the ID and epilepsy panels with green rating.

Consider inclusion in the current panel with amber rating [As authors discuss: some phenotypic features differed in their small cohort and the contribution of other recessive conditions in 2 consanguineous families cannot be excluded. Also: in fig S1 only status of parents but not of affected/unaffected sibs is specified with the exception of Fam1].
Sources: Literature
Created: 13 Mar 2022, 11:49 a.m.

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Delayed speech and language development; Global developmental delay; Intellectual disability; Seizures; Behavioral abnormality; Abnormality of the endocrine system; Hypothyroidism; Abnormality of nervous system morphology



Mode of Inheritance
BIALLELIC, autosomal or pseudoautosomal
  • Delayed speech and language development
  • Global developmental delay
  • Intellectual disability
  • Seizures
  • Behavioral abnormality
  • Abnormality of the endocrine system
  • Hypothyroidism
  • Abnormality of nervous system morphology
Clinvar variants
Variants in TIAM1
Panels with this gene

History Filter Activity

13 Mar 2022, Gel status: 0

Created, Added New Source, Set mode of inheritance, Set publications, Set Phenotypes, Set penetrance

Konstantinos Varvagiannis (Other)

gene: TIAM1 was added gene: TIAM1 was added to Intellectual disability. Sources: Literature Mode of inheritance for gene: TIAM1 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: TIAM1 were set to 35240055; 33328293 Phenotypes for gene: TIAM1 were set to Delayed speech and language development; Global developmental delay; Intellectual disability; Seizures; Behavioral abnormality; Abnormality of the endocrine system; Hypothyroidism; Abnormality of nervous system morphology Penetrance for gene: TIAM1 were set to Complete Review for gene: TIAM1 was set to AMBER