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Intellectual disability

Gene: PDZD8

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PDZD8 (PDZ domain containing 8)
EnsemblGeneIds (GRCh38): ENSG00000165650
EnsemblGeneIds (GRCh37): ENSG00000165650
OMIM: 614235, Gene2Phenotype
PDZD8 is in 1 panel

1 review

Konstantinos Varvagiannis (Other)

I don't know

Al-Amri et al (2022 - PMID: 35227461) describe 4 affected individuals, belonging to 2 independent consanguineous families, harboring biallelic pLoF PDZD8 variants. The phenotype corresponded to a syndromic form of ID with autistic features. Animal models provide additional evidence for a role of the gene.

Details are provided concerning 3 affected sibs born to consanguineous parents (Fam-A) and a male proband born to first cousin parents (Fam-B) from different countries of the Arabian Peninsula.

Features included DD (4/4), ID (4/4 - moderate to severe), autistic features[*](4/4), other behavioral problems (3/4 - 2 families). Variable facial features were observed (4/4 - incl. hypertelorism 4/4, myopathic face, open mouth, low-set ears, ptosis). 3 sibs presented with myopathy[*](3/4 overall - 1 fam - see below), and marfanoid habitus was observed in 2 (2/4 - 1 fam). 2 sibs had epilepsy (2/4 - from 1 family). 1 individual had congenital heart defect. [*] (also to consider for MOI) : Autistic features were however observed in a parent and a htz sib. Mild myopathy/reduced facial expression was also observed in both parents. Contribution of another variant - also within the region of shared homozygosity - to the phenotype of myopathy was deemed to be possible within this family.

Previous genetic testing was not reported.

Homozygosity mapping in the 1st family identified 3 homozygous regions (2.57 - 28 Mb) shared by all affected sibs. Singleton WES revealed 2 candidate variants within these regions, a PDZD8 frameshift variant [NM_173791.5:c.2197_2200del;p.(S733*)] lying in the last exon and an ANKRD2 missense one (discussed above).

The proband in Fam-B was hmz for a nonsense variant in ex2 (of 5), namely c.894C>G/p.(Y298*) considered to be the most likely cause of his phenotype following singleton WES.

Sanger sequencing was used for validation and segregation studies confirming carrier status of the parents and compatible results in unaffected sibs (tested : 2 in Fam-A, 3 in Fam-B).

Both variants were absent from gnomAD (the first also from a pool of 50 control individuals of the same origin) where PDZD8 has a pLI of 1 (5 different pLoF variants, none hmz).

Expression was not studied for the 2 variants. As a result, it is not known whether they escape NMD (as could be expected for the variant in the last exon).

PDZD8 encodes an endoplasmatic reticulum (ER) transmembrane protein (TM). As the authors discuss, it has been previously shown that depletion of PDZD8 in neurons impairs endosomal homeostasis, decreases proximity of ER-mitochondria and decreases Ca+2 uptake mitochondria following synaptic transmission-induced release from the ER (sev. refs. provided).

The gene is highly expressed in the human brain (incl. subclasses of GABAergic / glutamatergic neurons in adult primary motor cortex). The authors analyzed RNA-seq data from the BrainSpan project, demonstrating stable expression in human brain from 8 wks after conception to adulthood. The gene is not expressed in blood.

The authors performed in vivo functional studies. Knockdown of the orthologous gene (CG10362) in Drosophila via RNA interference was shown to result in impairment of long-term memory. Mice homozygous for a variant introducing a premature termination codon exhibited restricted growth, brain structural alterations (incl. relative reduction of the CC, as in one subject), spontaneous stereotypies, decreased anxiety-like behavior with deficits in spatial memory and impaired hippocampal neurophysiology.

Currently, there is no associated phenotype in OMIM, Gene2Phenotype, SysID or PanelApp Australia.

Overall, this gene can be considered for inclusion in the ID panel probably with amber rating pending further reports.
Sources: Literature
Created: 6 Mar 2022, 4:58 p.m. | Last Modified: 6 Mar 2022, 4:59 p.m.
Panel Version: 3.1506

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Global developmental delay; Intellectual disability; Autistic behavior; Behavioral abnormality; Myopathy; Abnormality of the face; Hypertelorism; Seizures; Disproportionate tall stature



Mode of Inheritance
BIALLELIC, autosomal or pseudoautosomal
  • Global developmental delay
  • Intellectual disability
  • Autistic behavior
  • Behavioral abnormality
  • Myopathy
  • Abnormality of the face
  • Hypertelorism
  • Seizures
  • Disproportionate tall stature
Clinvar variants
Variants in PDZD8
Panels with this gene

History Filter Activity

6 Mar 2022, Gel status: 0

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

Konstantinos Varvagiannis (Other)

gene: PDZD8 was added gene: PDZD8 was added to Intellectual disability. Sources: Literature Mode of inheritance for gene: PDZD8 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: PDZD8 were set to 35227461 Phenotypes for gene: PDZD8 were set to Global developmental delay; Intellectual disability; Autistic behavior; Behavioral abnormality; Myopathy; Abnormality of the face; Hypertelorism; Seizures; Disproportionate tall stature Penetrance for gene: PDZD8 were set to Complete Review for gene: PDZD8 was set to AMBER