Carney complex (CNC) is an autosomal dominant multiple neoplasia and lentiginosis syndrome characterised by spotty skin lesions, cardiac and other myxomas and different types of endocrine tumours. The
PRKAR1A
gene, which codes for the regulatory subunit type 1‐alpha of the cyclic
adenosine monophosphate
(cAMP)‐activated protein kinase A, is responsible for more than two‐thirds of the cases of CNC described to date. Currently, more than 120 different disease‐causing
PRKAR1A
sequence variants have been reported. Other involved genes for adrenal hyperplasias include phosphodiesterases
PDE11A
and
PDE8B
. Additional genes are likely to be identified that may expand our understanding on the pathophysiology of the cAMP signalling pathway and how genetic defects cause CNC and its individual components such as adrenal tumours.
Key Concepts:
Inactivating
PRKAR1A
mutations cause CNC because
PRKAR1A
haploinsufficiency leads to uncontrolled PKA activity.
The majority (∼80%) of
PRKAR1A
mutations causing CNC result in an early stop codon generation and degradation of the mutant RNA through nonsense‐mediated RNA decay (NMD).
Recently, novel types of
PRKAR1A
mutations have been described: large gene rearrangements and small indels resulting in an elongated protein through downstream shift of the stop codon.
The penetrance of
PRKAR1A
mutations is more than 95% by the age of 50 years.
PDE11A
and
PDE8B
genetic defects contribute to the CNC phenotype, but they may also independently cause forms of adrenal hyperplasia, mainly isolated micronodular adrenocortical disease (iMAD).
Genotype–phenotype correlation is limited, but there are certain mutations that cause more frequently certain endocrine manifestations such as isolated Cushing syndrome.
The use of new genomic techniques has led to the identification of new genetic defects in
PRKAR1A
and related genes in CNC.