Genetics of Carney Complex

Abstract

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.