Fetal anomalies
Gene: PRKACB
The rating of this gene has been updated to Green and the mode of inheritance set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown following NHS Genomic Medicine Service approval.Created: 10 Oct 2023, 3:39 p.m. | Last Modified: 10 Oct 2023, 3:39 p.m.
Panel Version: 3.111
Mode of inheritance
MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Comment on list classification: New gene added by Konstantinos Varvagiannis. There is sufficient evidence to promote this gene to Green at the next GMS panel update. At least 4 unrelated cases, displaying a ciliopathy-like phenotype.Created: 19 Nov 2020, 1:47 p.m. | Last Modified: 22 May 2023, 2:18 p.m.
Panel Version: 3.5
ID was a feature in 2/4 individuals with PRKACB pathogenic variant reported to date.
Please consider inclusion of PRKACB (and PRKACA) in other relevant gene panels e.g. for polydactyly, congenital heart defects. The disorder may be considered in the DD of ciliopathies.
-----
Palencia-Campos et al (2020 - PMID: 33058759) report on the phenotype of 3 individuals heterozygous for PRKACA and 4 individuals heterozygous for PRKACB pathogenic variants.
The most characteristic features in all individuals with PRKACA/PRKACB mutation, included postaxial polydactyly of hands (6/7 bilateral, 1/7 unilateral) and feet (4/7 bilateral, 1/7 unilateral), brachydactyly and congenital heart defects (CHD 5/7) namely a common atrium or AVSD. Two individuals with PRKACA variant who did not have CHD had offspring with the same variant and an AVSD.
Other variably occurring features included short stature, limbs, narrow chest, abnormal teeth, oral frenula, nail dysplasia. One individual with PRKACB variant presented tumors.
Intellectual disability was reported in 2/4 individuals with PRKACB variant (1/4: mild, 1/4: severe). The 3 individuals with PRKACA variant did not present ID.
As the phenotype was overall suggestive of Ellis-van Creveld syndrome (or the allelic Weyers acrofacial dysostosis), although these diagnoses were ruled out following analysis of EVC and EVC2 genes.
WES was carried out in all.
PRKACA : A single heterozygous missense variant was identified in 3 individuals from 3 families (NM_002730.4:c.409G>A / p.Gly137Arg) with 1 of the probands harboring the variant in mosaic state (28% of reads) and having 2 similarly affected offspring. The variant was de novo in one individual and inherited in a third one having a similarly affected fetus (narrow thorax, postaxial polyd, AVSD).
PRKACB : 4 different variants were identified (NM_002731.3: p.His88Arg/Asn, p.Gly235Arg, c.161C>T - p.Ser54Leu). One of the individuals was mosaic for the latter variant, while in all other cases the variant had occurred de novo.
Protein kinase A (PKA) is a tetrameric holoenzyme formed by the association of 2 catalytic (C) subunits with a regulatory (R) subunit dimer. Activation of PKA is achieved through binding of 2 cAMP molecules to each R-subunit, and unleashing(/dissociation) of C-subunits to engage substrates. PRKACA/B genes encode the Cα- and Cβ-subunits while the 4 functionally non-redundant regulatory subunits are encoded by PRKAR1A/1B/2A/2B genes.
The authors provide evidence that the variants confer increased sensitivity of PKA holoenzymes to activation by cAMP (compared to wt).
By performing ectopic expression of wt or mt PRKACA/B (variants studied : PRKACA p.Gly137Arg / PRKACB p.Gly235Arg) in NIH 3T3 fibroblasts, the authors demonstrate that inhibition of hedgehog signaling likely underlyies the developmental defects observed in affected individuals.
As for PRKACA, the authors cite another study where a 31-month old female with EvC syndrome diagnosis was found to harbor the aforementioned variant (NM_001304349.1:c.637G>A:p.Gly213Arg corresponding to NM_002730.4:c.409G>A / p.Gly137Arg) as a de novo event. Without additional evidence at the time, the variant was considered to be a candidate for this subject's phenotype (Monies et al 2019 – PMID: 31130284).
Sources: LiteratureCreated: 24 Oct 2020, 11:09 p.m.
Mode of inheritance
MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Phenotypes
Postaxial hand polydactyly; Postaxial foot polydactyly; Common atrium; Atrioventricular canal defect; Narrow chest; Abnormality of the teeth; Intellectual disability
Publications
Mode of pathogenicity
Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Tag Q2_23_promote_green was removed from gene: PRKACB.
Source Expert Review Green was added to PRKACB. Source NHS GMS was added to PRKACB. Rating Changed from Amber List (moderate evidence) to Green List (high evidence)
gene: PRKACB was added gene: PRKACB was added to Fetal anomalies. Sources: Expert Review Amber,Literature Q2_23_promote_green tags were added to gene: PRKACB. Mode of inheritance for gene: PRKACB was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: PRKACB were set to 33058759 Phenotypes for gene: PRKACB were set to Cardioacrofacial dysplasia 2, OMIM:619143 Penetrance for gene: PRKACB were set to unknown Mode of pathogenicity for gene: PRKACB was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments