Limb disorders

Gene: PRKACB

The rating of this gene has been updated following NHS Genomic Medicine Service approval.

Created: 5 Mar 2022, 8:17 p.m. | Last Modified: 5 Mar 2022, 8:17 p.m.

Panel Version: 2.67

Green List (high evidence)

Comment on list classification: There is sufficient evidence to promote this gene to Green at the next GMS panel update (added 'for-review' tag) - 4 unrelated cases, all presenting polydactyly of the hands and/or feet as well as other postaxial anomalies.

Created: 19 Nov 2020, 2:07 p.m. | Last Modified: 19 Nov 2020, 2:07 p.m.

Panel Version: 2.18

Palencia-Campos et al (2020 - PMID: 33058759) report on the phenotype of 4 individuals heterozygous for PRKACB pathogenic variants.

The most characteristic features in all individuals with PRKACB variants, included postaxial polydactyly of hands (3/4 bilateral, 1/4 unilateral) and feet (3/4 bilateral), clinodactyly (2/4), brachydactyly (1/4) and congenital heart defects (CHD 4/4) namely a common atrium or AVSD.

Other variably occurring features included short stature, limbs, narrow chest, abnormal teeth, oral frenula, nail dysplasia. One individual with PRKACB variant presented tumours. Intellectual disability was reported in 2/4 individuals with PRKACB variant (1/4: mild, 1/4: severe).

WES was carried out in all. 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 : PRKACB p.Gly235Arg) in NIH 3T3 fibroblasts, the authors demonstrate that inhibition of hedgehog signalling likely underlies the developmental defects observed in affected individuals.
Sources: Literature

Created: 19 Nov 2020, 2:03 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

• 33058759