Overview 

The hallmarks of Carney Complex (CNC) include skin pigmentation, endocrine tumours or overactivity and schwannomas.¹ The most prevalent symptoms are pale brown to black lentigines, which get worse during adolescence. Cardiac myxomas can develop in the cardiac chambers.¹ They can start early in life and present themselves as heart failure, intracardiac obstruction of blood flow or embolic pneumonia.¹ It's an autosomal dominant disorder which is characterised by multiple neoplasias at the sites of multiple endocrine glands and tissues.² The existence of the complex was first suggested in 1985. Although combinations of various syndrome components and their familial occurrence had been documented earlier. Thus, as early as 1949, the pathologic features of adrenal glands, including intranodular cortical atrophy and numerous tiny pigmented adrenocortical nodules, were reported in children and young adults with Cushing's syndrome.² Understanding the Carney complex inheritance patterns is essential for efficient clinical treatment and has significant consequences for several patient care areas. The illness being of an autosomal dominant nature means that a comprehensive approach to family-based medicine is required. Accurate knowledge of the inheritance patterns is needed in order to provide genetic counselling to affected families. According to research by Startakis et al (2001), approximately 70% of Carney complex cases occur in familial clusters.² This discovery completely revolutionised counselling protocols. It was established that each child of an affected parent has a 50% chance of inheriting the illness.² This indicates that the remaining 30% of CNC cases result from a de novo (new) pathogenic variant.⁶

Genetic basis 

Clinically and genetically, Carney complex is heterogeneous.⁴ For PRKARA1A mutations, there is a genotype-phenotype link since some tumours are more common with particular mutations. To begin with, Carney complex was described as endocrine overactivity, spotted skin pigmentation and a complex of myxomas.⁴ Identifying that inactivating germline mutations of regulatory subunit 1A (RIA) of cAMP-dependent protein kinase (PRKAR1A) gene in CNC patients resulted in the estimation of its penetrance and the proposal that there was no clear correlation between genotype and phenotype.⁴ An explanation for this was that all the identified PRKARA1A mutations in CNC patients resulted in nonsense mRNA, which did not translate into protein through the process of nonsense-mediated mRNA decay (NMD).⁴ Hence, all mutations had an identical effect. An absence of a detectable mutant protein and a decrease in the total RIA level by 50% through the translation of the wild-type allele.⁴ 

About two-thirds of patients with CNC have a germline mutation in the CNC gene 1, which is located at 17q22-24 in the regulatory subunit 1A of protein kinase A (PRKR1A).³ The second locus has been observed on chromosome 2p16. Patients with mutations in the PRKAR1A gene have been shown to have alterations in a locus at 2p16.³ Patients with non-pigmented adrenal hyperplasia or isolated micronodular pigmented adrenal disease have been found to have inactivating mutations of the phosphodiesterase genes PDE11A and, less frequently, PDE8B.³ 

These mutations play a part in the pathogenesis of CNC by causing premature stop codons or single-base alterations in the catalytic domain of the encoded proteins.

Autosomal dominant inheritance pattern:

Each cell has two copies of each gene. One is inherited from the mother, and one is inherited from the father. In an autosomal dominant pattern, a mutation happens in one copy of the gene. Consequently, the parent with a gene mutation may pass along a copy of their normal gene or a copy of the mutated gene.⁵ Therefore, Carney complex shows autosomal dominant inheritance, with approximately 80% of individuals affected inheriting the illness from an affected parent.⁵ Thus, family pedigree studies provide strong evidence for an autosomal dominant inheritance pattern in Carney complex. Pedigree analyses of multiple extensive families affected by the Carney complex unequivocally demonstrate this. Gender distribution data shows the predominance of females.⁶ This is likely due to a reduced male fertility resulting from Large Cell Calcified Sertoli Cell Tumours (LCCSCT).⁶ Furthermore, findings from animal models associate haploinsufficiency at the PRKR1A gene locus with male infertility.⁶ The disorder exhibits nearly complete penetrance. This indicates that an individual with a pathogenic variant has a high likelihood of developing symptoms.⁷ The penetrance of those with the PRKAR1A variant is more than 95% by the age of 50.⁹

The Carney complex also shows variable expressivity, meaning that different patients with the disorder show various signs or symptoms.⁸ Evidence for this is the wide array of tumours and lesions that can occur. The disorder can be characterised by endocrine manifestations such as pituitary tumours and gonadal tumours.³ Cardiac myxomas and breast lesions are also non-endocrine manifestations which can characterise the disorder.³ The engagement of numerous organ systems and variability can make diagnosis more difficult, typically necessitating multidisciplinary proficiency. Generally, clinical manifestations often emerge throughout adolescence and early adulthood. The median diagnostic age is 20 years. Nevertheless, symptoms of the disease, particularly cutaneous lesions, may be present in newborns.

Family risk assessment and patterns

Carney complex follows an autosomal dominant pattern, meaning that each child of an affected individual has a 50% chance of inheriting the disorder. A family risk assessment entails identifying those family members who are affected and conducting genetic testing for the PRKR1A gene.¹ Family members at risk require continuous surveillance and routine clinical and imaging assessments for tumours and hormonal issues.¹ Genetic counselling should also be provided to address testing, risks and reproductive options.¹ 

Gregory et al., endocrinologists, gave insight into how prepubertal children should be screened.⁶ A cardiac ultrasound should be conducted immediately after diagnosis. This should then subsequently be performed once yearly. This screening should be even more frequent for patients who have a history of cardiac myxoma, ideally every 6 months.⁶ Patients ought to receive an initial thyroid ultrasound through the first 10 years of life, with further examinations based on the results.⁶ Testicular ultrasonography is advised for males during the initial evaluation. If microcalcifications are detected, it should be repeated annually. In female patients, ovarian and breast imaging procedures may be postponed until after puberty. As pediatric patients with CNC may have developmental issues, it's important to keep an eye on pubertal staging and growth rate regularly.⁶

In post-pubertal adolescents and adults, the following assessments should be conducted at initial diagnosis and periodically afterwards.⁶ Screening for cardiac myxomas by echocardiography, if positive, should be conducted biannually.⁶ Screening for acromegaly through assessment of serum growth hormone (GH), prolactin (PRL) and insulin-like growth factor I (IGF I). In the event of aberrant findings, it is recommended to confirm GH hypersecretion by an oral glucose suppression test (OGTT).⁶

Future findings

A great amount of progress has been made since CNC was first described, although there is still plenty of work to be done. Ongoing research aims to develop more effective treatment options for the complications associated with Carney complex. One of the greatest challenges is the tendency of heart tumours to recur. Current research focuses on identifying the causes of recurrence and creating better management strategies, which involve more specialised treatments.¹⁰

FAQs

Can the Carney Complex be prevented?

It cannot be prevented if inherited, but early detection and monitoring can reduce complications.

Do all carriers show symptoms?

Not always. The Carney Complex shows variable expression and sometimes incomplete penetrance. Some family members may have mild or delayed symptoms, while others may develop serious complications.

Can the Carney Complex skip generations?

Not exactly. Because it is autosomal dominant, it does not skip generations genetically. However, variable expression means some family members may show very mild or late-onset symptoms, making it appear as though the condition skipped a generation.

Summary

The dominant recessive nature of the Carney complex means that knowledge of inheritance patterns is needed in order to provide genetic counselling to families. The great majority of patients with Carney complex have a germline mutation in the CNC gene. 80% of individuals with Carney complex inherited the illness from an affected parent. Therefore, family pedigrees provide strong evidence for the autosomal dominant inheritance pattern in Carney complex. The disorder shows variable expressivity, meaning symptoms within patients can vary. Family members at risk require constant surveillance and imaging assessments for tumours and hormonal issues. Also, identifying causes of recurrence of tumours to create a better quality of life for patients.