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Intellectual disability

Gene: PDE6D

Amber List (moderate evidence)

PDE6D (phosphodiesterase 6D)
EnsemblGeneIds (GRCh38): ENSG00000156973
EnsemblGeneIds (GRCh37): ENSG00000156973
OMIM: 602676, Gene2Phenotype
PDE6D is in 7 panels

2 reviews

Ellen McDonagh (Genomics England Curator)

Comment on list classification: Gene added by external reviewer, and promoted to Amber due to one family and a recent additional case.
Created: 29 Nov 2019, 2:44 p.m. | Last Modified: 29 Nov 2019, 2:44 p.m.
Panel Version: 2.1134

Konstantinos Varvagiannis (Other)

I don't know

Thomas et al. (2014 - PMID: 24166846) reported on a consanguineous Pakistani family with 3 members presenting variable polydactyly, brain anomalies (incl. molar tooth sign), microphthalmia/coloboma with retinal disease, renal hypoplasia suggestive of Joubert syndrome.

Genotyping with a SNP array identified a unique 17-Mb region of homozygosity on chr2 with LOD score of 2.6. The region contained 208 genes, of which 15 present in ciliary gene databases. A homozygous splicing variant appeared to be the only relevant, PDE6D being a ciliary gene within this region [NM_002601.4:c.140-1G>A]. Status of all affected members, parents and 2 unaffected sibs was verified with Sanger sequencing.

PDE6D encodes a phosphodiesterase that binds to prenyl groups and has a critical role in ciliogenesis (Humbert et al. - PMID: 23150559 and OMIM).
Several lines of evidence provided support a role for PDE6D and the reported variants :
- Study of PDE6D expression during human embryogenesis suggests ubiquitous localization and highest levels in organs affected in ciliopathies (CNS, kidney tubules, respiratory tract epitherlial cells).
- RT-PCR of mRNA from control/patient fibroblasts and sequencing confirmed the splicing defect leading to an in-frame deletion of exon 3.
- Wt and mutant protein both localized in the basal body of primary cilia (patient/control fibroblasts). Cilia in both cases had normal morphology.
- Experiments in RPE cells confirmed that INPP5E (involved in Joubert/MORM syndrome) interacts (/is probably a cargo of) PDE6D, a process dependent on prenylation.
- Exon 3 deletion was confirmed to disrupt PDE6D binding to INPP5E.
- Analysis by immunofluoresence of INPP5E localization using control/patient fibroblasts and renal tissue showed absence of INPP5E from primary cilia in the case of patient cells (but not controls) suggesting that PDE6D is important for trafficking INPP5E to the cilium.
- Previous study in mice suggested altered photoreceptor physiology in Pde6d (-/-) animals, resulting in a slowly progressing rod/cone dystrophy. The effect was however limited to the eye. (PMID cited : 17496142 - Zhang et al., 2007).
- Morpholino knockdown of pde6d resulted in pericardial edema, eye abnormalities (microphthalmia and disorganized retinal cell layers) and kidney morphogenesis defects (distended, blocked pronephric openings and proximal tubule cysts). Edema was rescued upon coinjection of morpholino with wt (but not mutant) mRNA. Similarly coinjection led to complete or partial rescue of eye development in the case of wt and mutant mRNA respectively supporting pathogenicity and (partial) loss-of-function effect for the variant.
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Mégarbané et al. (2019 - PMID: 30423442) reported on an affected 6 month-old boy born to Lebanese first-cousin parents. Features included hypotonia, developmental delay, microcephaly, oculomotor apraxia, postaxial polydactyly of hands and feet and presence of a molar tooth sign upon brain MRI. Renal and retinal anomalies were absent (also given his age). Exome sequencing revealed homozygosity for a frameshift PDE6D variant [NM_002601.3:c.367_368insG or p.(Leu123Cysfs*13)]. Sanger sequencing confirmed presence of the variant in the proband and carrier status of the parents. The variant affected the penultimate exon (note : present in only this longest transcript) and was not predicted to trigger NMD but rather lead to elimination of a highly conserved PDZ-interaction domain.
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The phenotype associated with biallelic PDE6D variants in OMIM is ?Joubert syndrome 22 - MIM 615665 based only on the 1st report ('delayed psychomotor development' among the features). There is no relevant entry in G2P. PDE6D is listed as a Current primary (/confirmed) ID gene in SysID (the aforementioned PMIDs cited).

This gene is included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx).
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Overall PDE6D could be considered for inclusion in the ID panel probably with amber rating (2 families/variants, DD but outcome otherwise unknown - evidence for the the gene causing JS seems however sufficient).
Sources: Literature
Created: 11 Nov 2019, 4:42 p.m.

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Phenotypes
?Joubert syndrome 22 - MIM 615665

Publications

Variants in this GENE are reported as part of current diagnostic practice

Details

Mode of Inheritance
BIALLELIC, autosomal or pseudoautosomal
Sources
Phenotypes
  • ?Joubert syndrome 22 - MIM 615665
OMIM
602676
Clinvar variants
Variants in PDE6D
Penetrance
Complete
Publications
Panels with this gene

History Filter Activity

29 Nov 2019, Gel status: 2

Entity classified by Genomics England curator

Ellen McDonagh (Genomics England Curator)

Gene: pde6d has been classified as Amber List (Moderate Evidence).

11 Nov 2019, Gel status: 0

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

Konstantinos Varvagiannis (Other)

gene: PDE6D was added gene: PDE6D was added to Intellectual disability. Sources: Literature Mode of inheritance for gene: PDE6D was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: PDE6D were set to 24166846; 30423442 Phenotypes for gene: PDE6D were set to ?Joubert syndrome 22 - MIM 615665 Penetrance for gene: PDE6D were set to Complete Review for gene: PDE6D was set to AMBER gene: PDE6D was marked as current diagnostic