A novel PRKAR1A mutation associated with hepatocellular carcinoma in a young patient and a variable Carney complex phenotype in affected subjects in older generations

Abstract

Context: Carney complex (CNC) is an autosomal dominant multiple endocrine neoplasia syndrome (OMIM 160980). About 70% of cases are familiar; most have mutations of the PRKAR1A gene on chromosome 17q22-24. There is little phenotype-genotype correlation known to date.

Objective: To study the genotype-phenotype correlation in a family with newly diagnosed CNC and three generations of subjects bearing the same PRKAR1A mutation. The proband was diagnosed with hepatocellular carcinoma, a tumour that appears to be associated with CNC.

Design: The study consisted of clinical and genetic analysis of a total of 10 individuals belonging to a large Italian family.

Patients: The index case was referred for PRKAR1A gene mutation analysis because he met the diagnostic criteria for a clinical diagnosis of CNC.

Results: The PRKAR1A-inactivating mutation c.502 +1G > A in the intron 5 splice-donor site was detected after bidirectional sequencing of germline DNA. The mutation causes a frameshift in the transcribed sequence and a nonsense mRNA that was shown to be degraded; this leads to PRKAR1A haploinsufficiency in all tissues. All available relatives were screened first by DNA testing and, if the latter was positive, by clinical, biochemical and imaging means.

Conclusions: A novel PRKAR1A mutation with an apparently low penetrance and variable expression is reported; the same mutation is also associated with a hepatocellular carcinoma. This is the first time a PRKAR1A mutation is reported in individuals who were diagnosed with CNC after retrospective family screening and following the identification of a proband; the finding has implications for genetic counselling on PRKAR1A and/or CNC.

Figure 1

Family CAR52 tree. Patients I.2, II.1-2-3-4 and III.1-2-3-4-5 underwent PRKAR1A analysis. Arrow indicates the index case.

Figure 2

RT-PCR on transformed lymphocytes from the affected family and control individuals. Lanes 1 and 2 – before cyclohexamide treatment; lanes 3 and 4, and, 6 and 7 – after 4 and 8 h, respectively, with cyclohexamide treatment – the abrogation of NMD allows expression of the shortened RNA, lacking exon 5 and containing premature stop codon. After gel extraction and purification, RT-PCR products were directly sequenced.

Figure 3

Loss of heterozygosity (LOH) analysis on liver tumour samples. (a) Schematic representation of the microsatellite markers of located on chromosome 17, the informative markers are bolded. (b) Graph representation of the tumour and the normal tissues – comparisons of the signal intensity; all the valued are averaged.