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Intellectual disability

Gene: PLXNA2

Amber List (moderate evidence)
PLXNA2 (plexin A2)
EnsemblGeneIds (GRCh38): ENSG00000076356
EnsemblGeneIds (GRCh37): ENSG00000076356
OMIM: 601054, Gene2Phenotype
PLXNA2 is in 1 panel

2 reviews

Ivone Leong (Genomics England Curator)

Comment on list classification: New gene added by Konstantinos Varvagiannis (Other). This gene is not associated with a phenotype in OMIM or Gene2Phenotype. As there are currently only 2 cases there is not enough evidence to support a gene-disease association. Therefore, this gene has been given an Amber rating.
Created: 6 Oct 2021, 2:14 p.m. | Last Modified: 6 Oct 2021, 2:14 p.m.
Panel Version: 3.1325
Created: 6 Oct 2021, 2:14 p.m.
Last Modified: 6 Oct 2021, 2:14 p.m.
Panel version: 3.1325

Konstantinos Varvagiannis (Other)

I don't know

Altuame et al (2021 - PMID: 34327814) describe 3 individuals from 2 consanguineous Arab families with biallelic PLXNA2 variants.

The index patient from the 1st family presented with CHD (hypoplastic right ventricle, ASD), DD and moderate ID (IQ of 40), failure to thrive as well as some dysmorphic features (obtuse mandibular angle, mild overbite, synophrys with downslanting p-f, strabismus, etc). There were additional features (eg. postaxial polydactyly) which were found in other affected and unaffected family members.

Exome sequencing with autozygome analysis revealed homozygosity for a PLXNA2 stopgain variant (NM_025179:c.3603C>A / p.(Cys1201*)).

Sanger confirmation was carried out and segregation analyses confirmed carrier status of the unaffected parents and a sib as well as a brother homozygous for the same variant. Clinical evaluation of the latter, following this finding revealed borderline intellectual functioning, ADHD, failure to thrive. There was no mandibular anomaly or overbite and no clinical evidence of CHD (no echo performed).

The index patient from the 2nd consanguineous family was evaluated for ID (IQ of 63), with previous borderline motor development, ADHD and some dysmorphic features (obtuse mandibular angle and overbite). There was no clinical evidence of CHD (no echo performed).

Exome sequencing with autozygosity mapping revealed a homozygous missense PLXNA2 variant (c.3073G>A / p.(Asp1025Asn), present only once in gnomAD (htz), with rather non-concordant in silico predictions SIFT 0.22, PolyPhen 0.682 and CADD 23.5. The aa was however highly conserved.

Segregation analysis confirmed carrier state of the parents and 2 unaffected sibs, with a 3rd sib homozygous for the wt allele.

As the authors discuss:
*PLXNA2 belongs to the plexin family of genes, encoding transmbembrane proteins functioning as semaphorin receptors. It has predominant expression in neural tissue. The protein is thought to bind semaphorin-3A, -3C or -5 followed by plexin A2 dimerization, activation of its GTPase-activating protein domain, negative regulation of Rap1B GTPase and initiation of a signal transduction cascade mediating axonal repulsion/guidance, dendritic guidance, neuronal migration.
*Murine Plxna2 knockout models display structural brain defects. In addition they display congenital heart defects incl. persistent truncus arteriosus and interrupted aortic arch.
*Rare CNVs in adult humans with tetralogy of Fallot have suggested a potential role of PLXNA2 in cardiac development and CHD.
*Expression and the role of PLXNA2 in human chondrocytes as well as a GWAS in 240 japanese patients with mandibular prognathism where PLXNA2 was suggested as a susceptibility locus.

Overall, the authors recognize some common features (as for cognitive functioning, some dysmorphic features incl. obtuse mandibular angle and overbite in 2 unrelated subjects, failure to thrive 3/3) and provide plausible explanations for the variability / discordance of others eg:
- Cyanotic heart disease explaining discordance in cognitive outcome among sibs
- Incomplete penetrance for CHD (and/or ID or mandibular anomaly) as for few AR disorders and/or
- Additional pathogenic variants possibly explaining the CHD in the first subject.

There is no associated phenotype in OMIM or G2P. SysID includes PLXNA2 among the candidate ID genes.
Sources: Literature, Other
Created: 14 Aug 2021, 4:52 p.m. | Last Modified: 14 Aug 2021, 4:54 p.m.
Panel Version: 3.1220

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Phenotypes
Intellectual disability; Abnormality of the face; Failure to thrive; Abnormal heart morphology

Publications

Created: 14 Aug 2021, 4:52 p.m.
Last Modified: 14 Aug 2021, 4:54 p.m.
Panel version: 3.1220

Details

Mode of Inheritance
BIALLELIC, autosomal or pseudoautosomal
Sources
  • Expert Review Amber
Phenotypes
  • Intellectual disability, MONDO:0001071
  • Abnormality of the face
  • Failure to thrive
  • Abnormal heart morphology
Tags
watchlist
OMIM
601054
Clinvar variants
Variants in PLXNA2
Penetrance
Incomplete
Publications
Panels with this gene

History Filter Activity

6 Oct 2021, Gel status: 2

Entity classified by Genomics England curator

Ivone Leong (Genomics England Curator)

Gene: plxna2 has been classified as Amber List (Moderate Evidence).

6 Oct 2021, Gel status: 0

Set Phenotypes

Ivone Leong (Genomics England Curator)

Phenotypes for gene: PLXNA2 were changed from Intellectual disability; Abnormality of the face; Failure to thrive; Abnormal heart morphology to Intellectual disability, MONDO:0001071; Abnormality of the face; Failure to thrive; Abnormal heart morphology

6 Oct 2021, Gel status: 0

Added Tag

Ivone Leong (Genomics England Curator)

Tag watchlist tag was added to gene: PLXNA2.

14 Aug 2021, Gel status: 0

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

Konstantinos Varvagiannis (Other)

gene: PLXNA2 was added gene: PLXNA2 was added to Intellectual disability. Sources: Literature,Other Mode of inheritance for gene: PLXNA2 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: PLXNA2 were set to 34327814 Phenotypes for gene: PLXNA2 were set to Intellectual disability; Abnormality of the face; Failure to thrive; Abnormal heart morphology Penetrance for gene: PLXNA2 were set to Incomplete Review for gene: PLXNA2 was set to AMBER