Utilisation of a cryptic non-canonical donor splice site of the gene encoding PARAFIBROMIN is associated with familial isolated primary hyperparathyroidism

Do Patients With Atypical Parathyroid Adenoma Need Close Follow-up?

CONTEXT

Atypical parathyroid adenomas (APAs) are neoplasms with uncertain malignant potential but lack unequivocal histological signs of malignancy.

OBJECTIVE

This work aims to retrospectively evaluate the clinical and biochemical profiles of patients with APA, the outcome after parathyroidectomy (PTX), and the presence of CDC73 germline and somatic mutations.

METHODS

This monocentric study was conducted on consecutive patients undergoing PTX for primary hyperparathyroidism (PHPT) between June 2000 and December 2020. Fifty-eight patients with a confirmed histopathological diagnosis of APA, and age- and sex-matched controls with parathyroid adenoma (PA) were also included.

RESULTS

Fifty-four patients had sporadic PHPT and 4 had familial isolated hyperparathyroidism (FIHP). Thirty-four patients (59%) had symptomatic disease. Serum calcium and parathyroid hormone (PTH) levels were significantly higher in symptomatic compared to asymptomatic patients (P = .048 and .008, respectively). FIHP patients were younger than their sporadic counterparts (30 ± 17 years vs 55 ± 13 years). APA patients had significantly higher serum calcium and PTH levels and lower 25-hydroxyvitamin D concentration, bone mineral density, and T score at one-third distal radius compared to those with PA. Four of 56 APA patients displayed a CDC73 germline mutation. No somatic CDC73 mutation was identified in 24 tumor specimens. The mean follow-up after surgery was 60 ± 56.4 months. All but 6 patients (90%), 5 with apparently sporadic PHPT and 1 with FIHP, were cured after surgery.

CONCLUSION

The large majority of patients with APA, despite a moderate/severe phenotype, have a good prognosis. Germline CDC73 mutation-positive patients had a higher rate of persistent/recurrent disease. CDC73 gene alterations do not seem to have a relevant role in the tumorigenesis of sporadic APA.

Benchmarking deep learning splice prediction tools using functional splice assays

Hereditary disorders are frequently caused by genetic variants that affect pre-messenger RNA splicing. Though genetic variants in the canonical splice motifs are almost always disrupting splicing, the pathogenicity of variants in the noncanonical splice sites (NCSS) and deep intronic (DI) regions are difficult to predict. Multiple splice prediction tools have been developed for this purpose, with the latest tools employing deep learning algorithms. We benchmarked established and deep learning splice prediction tools on published gold standard sets of 71 NCSS and 81 DI variants in the ABCA4 gene and 61 NCSS variants in the MYBPC3 gene with functional assessment in midigene and minigene splice assays. The selection of splice prediction tools included CADD, DSSP, GeneSplicer, MaxEntScan, MMSplice, NNSPLICE, SPIDEX, SpliceAI, SpliceRover, and SpliceSiteFinder-like. The best-performing splice prediction tool for the different variants was SpliceRover for ABCA4 NCSS variants, SpliceAI for ABCA4 DI variants, and the Alamut 3/4 consensus approach (GeneSplicer, MaxEntScacn, NNSPLICE and SpliceSiteFinder-like) for NCSS variants in MYBPC3 based on the area under the receiver operator curve. Overall, the performance in a real-time clinical setting is much more modest than reported by the developers of the tools.

Genetic Alteration Profiles and Clinicopathological Associations in Atypical Parathyroid Adenoma

Genomic aberrations associated with atypical parathyroid adenoma (AA) are poorly understood. Thus, herein, we sought to expand our current understanding of the molecular basis of atypical parathyroid adenomas. We analyzed 134 samples that had been surgically obtained from parathyroid tumors, including parathyroid carcinomas, atypical parathyroid adenomas, and parathyroid adenomas. The tumors were harvested from formalin-fixed, paraffin-embedded tissues. Fifteen tumor-related genes from recently published genome sequencing data were subjected to targeted sequencing analysis, and an average sequencing depth of 500x was achieved. Sixteen (16/50, 32%) AA tumors harbored at least one of the following genomic alterations: CDC73 (12, 24%), EZH2 (4, 8%), HIC1 (1, 2%), and CDKN2A (1, 2%). Our study identified, for the first time, a relatively high frequency of genomic alterations in patients with AA in a Chinese population. This suggests that AA arises de novo, rather than developing from a parathyroid adenoma. Altogether, these findings will improve our understanding of the malignant potential of parathyroid tumors at the molecular level.

Rare Somatic MEN1 Gene Pathogenic Variant in a Patient Affected by Atypical Parathyroid Adenoma

OBJECTIVE

Atypical parathyroid adenoma is a rare neoplasm, showing atypical histological features intermediate between classic benign adenoma and the rarest parathyroid carcinoma, whose the clinical behaviour and outcome is not yet understood or predictable. Up to date only two cases of atypical adenoma were found associated to a MEN1 syndrome, and only one was proved to carry a pathogenic variant of the MEN1 gene.

DESIGN

We report the clinical, histologic, and molecular findings of a 44-year-old woman, presenting with a histologically proved atypical parathyroid adenoma with an apparent aggressive behaviour.

METHODS AND RESULTS

CDC73 gene was screened at germline and somatic levels with no results. Whole exome sequencing performed on DNA extracted from blood leukocytes and tumour tissue revealed a somatic MEN1 gene heterozygous variant, c.912+1G > A, of the splicing donor site of exon 6. On immunohistochemistry, downregulation of the menin protein expression in the neoplastic cells was also observed.

CONCLUSIONS

We report the second case of a rare association of a somatic MEN1 gene mutation in a patient with atypical parathyroid adenoma. We suggest that MEN1 gene could be an underestimate genetic determinant of these rare histological entities, and we highlight the utility of a complete genetic screening protocol, by the use of next-generation sequencing technology in such undetermined clinical cases with no frank clinical presentation.

Primary hyperparathyroidism in Chinese children and adolescents: A single-centre experience at Peking Union Medical College Hospital

OBJECTIVE

Primary hyperparathyroidism (PHPT) in children is thought to be extremely rare. Our study aimed to summarize the clinical characteristics and the molecular genetics in patients with paediatric PHPT in China.

DESIGN

Retrospective observational study.

METHODS

A total of 59 paediatric PHPT patients (onset age <18 years) admitted to Peking Union Medical College Hospital from 1975 to 2015 were retrospectively identified. A group of 118 adult PHPT patients who presented during the same period were selected for comparing clinical characteristics between the two groups. Germline mutation analyses of the MEN1, CDC73, RET, CDKN1B and CaSR genes were performed in 24 patients.

RESULTS

Only one paediatric patient (1.7%) with PHPT was asymptomatic. Bone involvement, urolithiasis, acute pancreatitis and hypercalcaemic crisis were present in 86.4%, 39.0%, 6.8% and 10.2% of cases, respectively. Paediatric PHPT presented more commonly with rickets/osteomalacia compared to adult PHPT. Fifty-seven paediatric patients underwent surgery. Adenoma, hyperplasia, atypical adenoma and carcinoma occurred in 80.7%, 10.5%, 7.0% and 1.8% of cases, respectively. Of the 24 paediatric patients screened for genetic mutations, two patients were found to carry MEN1 mutations and six were found to carry CDC73 mutations. The mutation rate was 22.2% (4/18) in sporadic patients.

CONCLUSION

Unlike adults with PHPT, most paediatric PHPT were symptomatic. Rickets/osteomalacia was more common in paediatric patients than in their adult counterparts. Paediatric PHPT patients can be treated successfully with surgical intervention. Genetic screening of the MEN1 and CDC73 genes for mutations should be recommended in paediatric patients due to a relatively high mutation rate.

Molecular genetics of syndromic and non-syndromic forms of parathyroid carcinoma

Parathyroid carcinoma (PC) may occur as part of a complex hereditary syndrome or an isolated (i.e., non‐syndromic) non‐hereditary (i.e., sporadic) endocrinopathy. Studies of hereditary and syndromic forms of PC, which include the hyperparathyroidism‐jaw tumor syndrome (HPT‐JT), multiple endocrine neoplasia types 1 and 2 (MEN1 and MEN2), and familial isolated primary hyperparathyroidism (FIHP), have revealed some genetic mechanisms underlying PC. Thus, cell division cycle 73 (CDC73) germline mutations cause HPT‐JT, and CDC73 mutations occur in 70% of sporadic PC, but in only ∼2% of parathyroid adenomas. Moreover, CDC73 germline mutations occur in 20%–40% of patients with sporadic PC and may reveal unrecognized HPT‐JT. This indicates that CDC73 mutations are major driver mutations in the etiology of PCs. However, there is no genotype–phenotype correlation and some CDC73 mutations (e.g., c.679_680insAG) have been reported in patients with sporadic PC, HPT‐JT, or FIHP. Other genes involved in sporadic PC include germline MEN1 and rearranged during transfection (RET) mutations and somatic alterations of the retinoblastoma 1 (RB1) and tumor protein P53 (TP53) genes, as well as epigenetic modifications including DNA methylation and histone modifications, and microRNA misregulation. This review summarizes the genetics and epigenetics of the familial syndromic and non‐syndromic (sporadic) forms of PC.

Parathyroid cancer and the CDC73 tumor suppressor gene

Parathyroid carcinoma (PC) is a rare endocrine neoplasm, usually causing severe primary hyperparathyroidism, that frequently causes death from unmanageable hypercalcemia. PC is frequently associated with somatic inactivating mutations of the CDC73 gene (previously called HRPT2), a gene discovered in association with the familial hyperparathyroidism-jaw tumor syndrome. DNA analysis for CDC73 mutation should be performed on all patients with seemingly sporadic PC since some 25% will carry a germline mutation. It is often difficult to make a firm diagnosis of PC by histopathology alone. That diagnosis often depends on the presence of local tissue invasion or distant metastases. If PC is suspected, en bloc resection at initial surgery is recommended. Medical therapy with cinacalcet, bisphosphonates or denosumab may temporarily ameliorate the hypercalcemia of inoperable PC.

Genetic basis of familial isolated hyperparathyroidism: a case series and a narrative review of the literature

Primary hyperparathyroidism is a heterogeneous clinical entity. In the clinical setting, the diagnosis and management of familial isolated hyperparathyroidism (FIHP) and other familial hyperparathyroidism (FHPT) forms continue to rely on clinical, laboratory, and histological findings, with careful examination of the family. In this article, we report a case series of FIHP in a four-generation Greek family, with no identifiable gene mutations. Clinical approach and long-term follow-up are discussed and a narrative review of the genetic basis of this entity has been performed.

Nocturnal light environments influence color vision and signatures of selection on the OPN1SW opsin gene in nocturnal lemurs

Although loss of short-wavelength-sensitive (SWS) cones and dichromatic color vision in mammals has traditionally been linked to a nocturnal lifestyle, recent studies have identified variation in selective pressure for the maintenance of the OPN1SW opsin gene (and thus, potentially dichromacy) among nocturnal mammalian lineages. These studies hypothesize that purifying selection to retain SWS cones may be associated with a selective advantage for nocturnal color vision under certain ecological conditions. In this study, we explore the effect of nocturnal light environment on OPN1SW opsin gene evolution in a diverse sample of nocturnal lemurs (106 individuals, 19 species, and 5 genera). Using both phylogenetic and population genetic approaches, we test whether species from closed canopy rainforests, which are impoverished in short-wavelength light, have experienced relaxed selection compared with species from open canopy forests. We identify clear signatures of differential selection on OPN1SW by habitat type. Our results suggest that open canopy species generally experience strong purifying selection to maintain SWS cones. In contrast, closed canopy species experience weaker purifying selection or a relaxation of selection on OPN1SW. We also found evidence of nonfunctional OPN1SW genes in all Phaner species and in Cheirogaleus medius, implying at least three independent losses of SWS cones in cheirogaleids. Our results suggest that the evolution of color vision in nocturnal lemurs has been influenced by nocturnal light environment.

Molecular diagnosis of primary hyperparathyroidism in familial cancer syndromes

In the last few years, causative genes have been identified for most of the familial hyperparathyroidism conditions. Germline mutations in the tumour suppressors multiple endocrine neoplasia type 1 (MEN1) and hyperparathyroidism 2 (HRPT2) provide a molecular diagnosis of multiple endocrine neoplasia type 1 and hyperparathyroidism jaw tumour syndrome, respectively. Germline mutations in the proto-oncogene RET (rearranged during transfection) provide a molecular diagnosis of multiple endocrine neoplasia type 2. Germline mutations of both MEN1 and, less frequently HRPT2, have been found in familial isolated hyperparathyroidism. A molecular diagnosis can now be incorporated into the management of patients with these conditions, however, the ease of diagnostics and value of genetic information in the context of clinical screening and early surgical intervention varies between these disorders. This review focuses on familial hyperparathyroidism and its known causative genes in the setting of neoplastic syndromes, with particular discussion of recent developments in the molecular diagnosis of parathyroid carcinoma.

Oncogenic microRNA-155 down-regulates tumor suppressor CDC73 and promotes oral squamous cell carcinoma cell proliferation: implications for cancer therapeutics

The CDC73 gene is mutationally inactivated in hereditary and sporadic parathyroid tumors. It negatively regulates β-catenin, cyclin D1, and c-MYC. Down-regulation of CDC73 has been reported in breast, renal, and gastric carcinomas. However, the reports regarding the role of CDC73 in oral squamous cell carcinoma (OSCC) are lacking. In this study we show that CDC73 is down-regulated in a majority of OSCC samples. We further show that oncogenic microRNA-155 (miR-155) negatively regulates CDC73 expression. Our experiments show that the dramatic up-regulation of miR-155 is an exclusive mechanism for down-regulation of CDC73 in a panel of human cell lines and a subset of OSCC patient samples in the absence of loss of heterozygosity, mutations, and promoter methylation. Ectopic expression of miR-155 in HEK293 cells dramatically reduced CDC73 levels, enhanced cell viability, and decreased apoptosis. Conversely, the delivery of a miR-155 antagonist (antagomir-155) to KB cells overexpressing miR-155 resulted in increased CDC73 levels, decreased cell viability, increased apoptosis, and marked regression of xenografts in nude mice. Cotransfection of miR-155 with CDC73 in HEK293 cells abrogated its pro-oncogenic effect. Reduced cell proliferation and increased apoptosis of KB cells were dependent on the presence or absence of the 3'-UTR in CDC73. In summary, knockdown of CDC73 expression due to overexpression of miR-155 not only adds a novelty to the list of mechanisms responsible for its down-regulation in different tumors, but the restoration of CDC73 levels by the use of antagomir-155 may also have an important role in therapeutic intervention of cancers, including OSCC.

Transcription variants of SLA-7, a swine non classical MHC class I gene

In pig, very little information is available on the non classical class I (Ib) genes of the Major Histocompatibility Complex (MHC) i.e. SLA-6, -7 and -8. Our aim was to focus on the transcription pattern of the SLA-7 gene. RT-PCR experiments were carried out with SLA-7 specific primers targeting either the full coding sequence (CDS) from exon 1 to the 3 prime untranslated region (3UTR) or a partial CDS from exon 4 to the 3UTR. We show that the SLA-7 gene expresses a full length transcript not yet identified that refines annotation of the gene with eight exons instead of seven as initially described from the existing RefSeq RNA. These two RNAs encode molecules that differ in cytoplasmic tail length. In this study, another SLA-7 transcript variant was characterized, which encodes a protein with a shorter alpha 3 domain, as a consequence of a splicing site within exon 4. Surprisingly, a cryptic non canonical GA-AG splicing site is used to generate this transcript variant. An additional SLA-7 variant was also identified in the 3UTR with a splicing site occurring 31 nucleotides downstream to the stop codon. In conclusion, the pig SLA-7 MHC class Ib gene presents a complex transcription pattern with two transcripts encoding various molecules and transcripts that do not alter the CDS and may be subject to post-transcriptional regulation.

Parathyroid cancer

Parathyroid cancer is an uncommon malignancy and rare cause of primary hyperparathyroidism (HPT) with a high morbidity and patient death in advanced cases usually resulting from intractable hypercalcemia. Inactivation of the HRPT2/CDC73 gene, encoding the putative tumor-suppressor protein parafibromin and discovered in the context of the hyperparathyroidism-jaw tumor (HPT-JT) syndrome, is a common, somatic event in most parathyroid cancers. Approximately 25% of patients with apparently sporadic parathyroid cancer carry germline HRPT2/CDC73 mutation. Germline DNA analysis for HRPT2/CDC73 mutation is recommended in all patients with parathyroid cancer because of the potential benefit for first-degree relatives, who should nevertheless undergo serum calcium screening. The histopathologic diagnosis of parathyroid cancer is nonspecific unless vascular, lymphatic, capsular, or soft tissue invasion is seen, or metastases are clinically evident. Immunohistochemical analysis of parathyroid tumors for loss of parafibromin expression offers promise as a diagnostic tool. En bloc tumor resection offers the highest chance of cure in patients with suspected parathyroid carcinoma. No adjuvant chemotherapy regimen has yet proven effective, and the role of local adjuvant radiotherapy is being evaluated. Metastatic disease can be palliated with surgical debulking. Medical therapy with the calcimimetic cinacalcet and bisphosphonates can ameliorate hypercalcemia in patients with inoperable disease.

Parathyroid carcinoma

Parathyroid carcinoma is a rare endocrine malignancy. The reported incidence is from 0.5 to 5% of primary hyperparathyroidism cases in various series. The cause is unknown, but clinical correlations with different genetic syndromes exist. Mutations in the HPRT2 gene seem to play a significant role in the pathogenesis of this disease. Men and women are equally affected, usually in the fourth or fifth decade of life. Most patients will present with signs and symptoms of hypercalcaemia. Cases of non-functioning carcinoma are exceedingly rare. Surgical resection is the most effective method of treatment and palliation. A significant proportion of patients will experience recurrence, and will need further surgical and, eventually, medical management of hypercalcaemia. The disease is progressive but slow growing. Most patients will require multiple operations to resect recurrent disease. The main cause of morbidity and mortality is the sequela of uncontrolled chronic hypercalcaemia rather than tumour burden. The current paper will review the epidemiology, pathogenesis, clinical presentation and diagnostic work-up of this disease. Surgical management in different scenarios is reviewed in detail, followed by other types of treatment and management of incurable disease.

Hyperparathyroidism-jaw tumor syndrome: a case report

We report the clinical and genetic findings in a 23-year-old woman with hyperparathyroidism-jaw tumor syndrome (HPT-JT). The patient had a family history of primary hyperparathyroidism (PHPT) and uterine fibroma in her mother. The patient presented muscle weakness. The diagnosis of PHPT was confirmed by an elevated parathyroid hormone level above 1450 pg/ml with hypercalcemia and hypercalciuria. X-ray radiographies showed a radiolucent lesion in the right body of the mandible. Bilateral neck exploration was performed. An inferior right parathyroidectomy, a left thyroid lobectomy with isthmectomy and thymectomy were carried out. Histopathological examination of the specimen showed a diffuse hyperplasia of the parathyroid principal cells. The association of PHPT with a right jaw tumor and uterine fibroma suggested the diagnosis of HPT-JT syndrome. Mutation screening of HRPT2 gene was carried out and identified a germline mutation, consisting in a base deletion in exon 1, 85delG, inducing a frameshift. The diagnosis of HPT-JT syndrome is clinically important because of its hereditary component and its high risk of parathyroid malignancy, making a genetic inquiry necessary.

Parafibromin--functional insights

Parafibromin is a predominantly nuclear protein with a tumour suppressor role in the development of hereditary and nonhereditary parathyroid carcinomas, and the hyperparathyroidism-jaw tumour syndrome, which is associated with renal and uterine tumours. Parafibromin is a component of the highly conserved PAF1 complex, which regulates transcriptional events and histone modifications. The parafibromin/PAF1 complex regulates genes involved in cell growth and survival, and via these, parafibromin plays a pivotal role in embryonic development and survival of adults.

HRPT2 gene analysis and the diagnosis of parathyroid carcinoma

Parathyroid carcinoma is an uncommon cause of primary hyperparathyroidism (PHPT) and is usually associated with more severe clinical manifestations than its much more common benign counterpart, the parathyroid adenomas. The histopathological distinction between benign and malignant parathyroid tumors is difficult. Currently, pathological diagnosis of parathyroid carcinoma is restricted to lesions showing unequivocal growth, as evidenced by perineural invasion, full-thickness capsular invasion with growth into adjacent tissues, or metastasis. Major advances in the molecular pathogenesis of parathyroid carcinoma have been made by the cloning of the HRPT2 gene, which encodes parafibromin, a 531-amino acid putative tumor-suppressor protein. Germline mutations of HRPT2 confer susceptibility to the hyperparathyroidism-jaw tumor syndrome (HPT-JT), an autosomal dominant syndrome with high but incomplete penetrance. Somatic inactivating mutations of the HRPT2 gene have been reported in the majority of apparently sporadic parathyroid carcinomas but, unexpectedly, germline HRPT2 mutation have been found in up to 30% of these patients. Several studies have been performed to evaluate whether parafibromin immunostaining might have some diagnostic utility. Loss of parafibromin immunoreactivity has been found in the majority of parathyroid carcinomas, in 50% of equivocal carcinomas and, very rarely, in benign adenomas. On the other hand, with the exception of HPT-JT-related tumors, loss of parafibromin associated with HRPT2 mutations strongly predicts parathyroid malignancy. In clinical practice, parafibromin immunostaining and HRPT2 gene analysis could be particularly useful in the subset of parathyroid tumors with equivocal histology.

Cryptic splicing sites are differentially utilized in vivo

It has long been considered that cryptic splice sites are ignored by the splicing machinery in the context of intact genuine splice sites. In the present study, it is shown that cryptic splice sites are utilized in all circumstances, when the authentic site is intact, partially functional or completely abolished. Their use would therefore contribute to a background lack of fidelity in the context of the wild-type sequence. We also found that a mutation at the 5' splice site of beta-globin intron 1 accommodates multiple cryptic splicing pathways, including three previously reported pathways. Focusing on the two major cryptic 5' splice sites within beta-globin exon 1, we show that cryptic splice site selection ex vivo varies depending upon: (a) the cell stage of development during terminal erythroid differentiation; (b) the nature of the mutation at the authentic 5' splice site; and (c) the nature of the promoter. Finally, we found that the two major cryptic 5' splice sites are utilized with differential efficiencies in two siblings sharing the same beta-globin chromosome haplotype in the homozygous state. Collectively, these data suggest that intrinsic, sequence specific factors and cell genetic background factors both contribute to promote a subtle differential use of cryptic splice sites in vivo.

Familial isolated primary hyperparathyroidism caused by mutations of the MEN1 gene

BACKGROUND

Familial isolated primary hyperparathyroidism (FIHP) is an autosomal dominant disorder that can represent an early stage of either the multiple endocrine neoplasia type 1 (MEN1) or hyperparathyroidism-jaw tumor (HPT-JT) syndromes; alternatively, the condition can be caused by an allelic variant of MEN1 or HRPT2 (hyperparathyroidism 2 gene), or caused by a distinct entity involving another locus. We have explored these possibilities in a patient with primary hyperparathyroidism, whose mother had a history of renal calculi and primary hyperparathyroidism.

INVESTIGATIONS

Serum biochemistry and radiological investigations for primary hyperparathyroidism, MEN1 and HPT-JT, and genetic testing for MEN1 and HRPT2 mutations were undertaken.

DIAGNOSIS

FIHP with primary hyperparathyroidism as the sole endocrinopathy due to a previously unreported heterozygous missense germline MEN1 mutation, Tyr351Asn. In addition, another unreported heterozygous missense germline MEN1 mutation, Trp220Leu, was identified in an unrelated male patient with FIHP, whose mother and sister also had primary hyperparathyroidism. DNA from a parathyroid tumor from the sister revealed a loss of heterozygosity in which the mutant allele was retained. This is consistent with Knudson's 'two-hit' model of hereditary cancer and a tumor suppressor role for MEN1 in FIHP.

MANAGEMENT

The patient underwent parathyroidectomy and has remained normocalcemic over a follow-up period of 6 years. The other four patients have remained normocalcemic for a follow-up period of 4-15 years following parathyroidectomy. None has developed abnormalities of the MEN1 syndrome, providing further support that FIHP is a distinct genetic variant of the MEN1 syndrome.

Downregulated parafibromin expression is a promising marker for pathogenesis, invasion, metastasis and prognosis of gastric carcinomas

Parafibromin is a protein encoded by the hyperparathyroidism 2 oncosuppressor gene and its downregulated expression is involved in pathogenesis of parathyroid carcinomas. To clarify the roles of parafibromin expression in tumourigenesis and progression of gastric carcinomas, it was examined by immunohistochemistry (IHC) on tissue microarray containing gastric carcinomas (n = 508), adenomas (n = 45) and gastritis (n = 49) with a comparison of its expression with clinicopathological parametres of carcinomas. Gastric carcinoma cell lines (MKN28, AGS, MKN45, KATO-III and HGC-27) were studied for parafibromin expression by IHC and western blot. Parafibromin expression was localised in the nucleus of gastric epithelial cells, adenoma, carcinoma cells and cell lines. Its expression was gradually decreased from gastritis to gastric carcinoma, through gastric adenomas (p < 0.05) and inversely correlated with tumour size, depth of invasion, lymphatic invasion, lymph node metastasis and Union Internationale Contre le Cancer (UICC) staging (p < 0.05) but not with sex or venous invasion (p > 0.05). Parafibromin was strongly expressed in older carcinoma patients compared with younger ones (p < 0.05). There was stronger positivity of parafibromin in intestinal-type than diffuse-type carcinomas (p < 0.05). Univariate analysis indicated cumulative survival rate of patients with positive parafibromin expression to be higher than without its expression (p < 0.05). Multivariate analysis showed that age, tumour size, depth of invasion, lymphatic invasion, lymph node metastasis, UICC staging and Lauren’s classification but not sex, venous invasion or parafibromin expression were independent prognostic factors for carcinomas(p < 0.05). Downregulated parafibromin expression possibly contributed to pathogenesis, growth, invasion and metastasis of gastric carcinomas. It was considered as a promising marker to indicate the aggressive behaviours and prognosis of gastric carcinomas.

Targeted knockout and lacZ reporter expression of the mouse Tmhs deafness gene and characterization of the hscy-2J mutation

The Tmhs gene codes for a tetraspan transmembrane protein that is expressed in hair cell stereocilia. We previously showed that a spontaneous missense mutation of Tmhs underlies deafness and vestibular dysfunction in the hurry-scurry (hscy) mouse. Subsequently, mutations in the human TMHS gene were shown to be responsible for DFNB67, an autosomal recessive nonsyndromic deafness locus. Here we describe a genetically engineered null mutation of the mouse Tmhs gene (Tmhs ( tm1Kjn )) and show that its phenotype is identical to that of the hscy missense mutation, confirming the deleterious nature of the hscy cysteine-to-phenylalanine substitution. In the targeted null allele, the Tmhs promoter drives expression of a lacZ reporter gene. Visualization of beta-galactosidase activity in Tmhs ( tm1Kjn ) heterozygous mice indicates that Tmhs is highly expressed in the cochlear and vestibular hair cells of the inner ear. Expression is first detectable at E15.5, peaks around P0, decreases slightly at P6, and is absent by P15, a duration that supports the involvement of Tmhs in stereocilia development. Tmhs reporter gene expression also was detected in several cranial and cervical sensory ganglia, but not in the vestibular or spiral ganglia. We also describe a new nontargeted mutation of the Tmhs gene, hscy-2J, that causes abnormal splicing from a cryptic splice site within exon 2 and is predicted to produce a functionally null protein lacking 51 amino acids of the wild-type sequence.

A novel MEN1 intronic mutation associated with multiple endocrine neoplasia type 1

OBJECTIVE

To investigate a family with an unusual combination of multiple endocrine neoplasia (MEN1) and the McCune-Albright syndrome for MEN1 mutations and activating GNAS1 mutations at codons Arg201 and Gln227.

METHODS

DNA sequences analyses were performed of the MEN1 gene and codons Arg201 and Gln227 of the GNAS1 gene, using leucocyte and endocrine tissue DNA.

RESULTS

A c-->g transversion at position -9 bp in intron 9 of the MEN1 gene was identified. This resulted in the generation of a BmrI restriction endonuclease site, and its presence and segregation with MEN1 in the family was demonstrated by restriction endonuclease analysis. The c-->g transversion was shown to result in the generation of a novel acceptor splice site (ccag) using reverse transcriptase-polymerase chain reaction (RT-PCR) and ribonucleic acid (RNA) obtained from Epstein-Barr virus (EBV)-transformed lymphoblasts. Utilization of this splice site resulted in an abnormal messenger RNA (mRNA) transcript that contained an additional eight bases. This predicted a frameshift that would result in nine missense amino acids followed by a premature termination signal. GNAS1 mutations were not detected in the patient with McCune-Albright syndrome.

CONCLUSIONS

The occurrence of MEN1 and the McCune-Albright syndrome in this family are coincidental findings and not due to a common genetic aetiology. However, our results have identified a novel MEN1 mutation that occurs in intron 9 and generates a novel acceptor splice site. Such splicing-affecting genomic variants (SpaGVs) are increasingly being recognized as a cause of human disease, and are likely to be of significance in the 10% of MEN1 patients who do not have coding region mutations.

Characterisation of a bis(5'-nucleosyl)-tetraphosphatase (asymmetrical) from Drosophila melanogaster

The intracellular functions of diadenosine polyphosphates are still poorly defined. To understand these better, we have expressed and characterized a heat stable, 16.6kDa Nudix hydrolase (Apf) that specifically metabolizes these nucleotides from a Drosophila melanogaster cDNA. Apf always produces an NTP product, with substrate preference depending on pH and divalent ion (Zn(2+) or Mg(2+)). For example, diadenosine tetraphosphate is hydrolysed to ATP and AMP with K(m), k(cat) and k(cat)/K(m) values 9microM, 43s(-1) and 4.8microM(-1)s(-1) (pH 6.5, 0.1mMZn(2+)) and 12microM, 13s(-1) and 1.1microM(-1)s(-1) (pH 7.5, 20mMMg(2+)), respectively. However, diadenosine hexaphosphate is efficiently hydrolysed to ATP only at pH 7.5 with 20mMMg(2+) (K(m), k(cat) and k(cat)/K(m) values of 15microM 4.0s(-1), and 0.27microM(-1)s(-1)). Fluoride potently inhibits diadenosine tetraphosphate hydrolysis in the presence of Mg(2+) (IC(50)=20microM), whereas it is ineffective in the presence of Zn(2+), supporting the view that inhibition involves a specific, MgF(3)(-)-containing transition state analogue complex. Patterns of Apf expression in Drosophila tissues show Apf mRNA levels to be highest in embryos and adult females. Subcellular localization with Apf-EGFP fusion constructs reveals Apf to be predominantly nuclear, having an apparent preferential association with euchromatin and facultative heterochromatin. This supports a nuclear function for diadenosine tetraphosphate. Our results show Apf to be a fairly typical member of the bis (5'-nucleosyl)-tetraphosphatase subfamily of Nudix hydrolases with features that distinguish it from a previously reported bis (5'-nucleosyl)-tetraphosphatase hydrolase activity from Drosophila embryos.

Genetic analyses in patients with familial isolated hyperparathyroidism and hyperparathyroidism-jaw tumour syndrome

BACKGROUND

A subset of familial isolated primary hyperparathyroidism (FIHP) is a variant of hyperparathyroidism-jaw tumour syndrome (HPT-JT). AIM/PATIENTS AND METHODS: We investigated the involvement of the HRPT2, MEN1 and CASR genes in 11 provisional FIHP families and two HPT-JT families.

RESULTS

Germline mutations of HRPT2 were found in two of the 11 FIHP families and one of the two HPT-JT families. One FIHP family with parathyroid carcinoma and atypical adenomas and another FIHP family with cystic parathyroid adenoma had novel frameshift mutations of 518-521del and 62-66del, respectively. In a patient with HPT-JT, a de novo germline mutation of 39delC was detected. Novel somatic HRPT2 mutations of 70-73del and 95-102del were found in two of five parathyroid tumours in a family with a 518-521del mutation. Biallelic inactivation of HRPT2 by a combination of germline and somatic mutation was confirmed in the parathyroid tumours. The finding that two families diagnosed with FIHP carried HRPT2 mutations suggests that they have occult HPT-JT. In the remaining 10 families, one family had a missense MEN1 mutation. No mutations of CASR were detected.

CONCLUSION

Our results confirm the need to test for HRPT2 in FIHP families, especially those with parathyroid carcinomas, atypical adenomas or adenomas with cystic change.

Parafibromin mutations in hereditary hyperparathyroidism syndromes and parathyroid tumours

OBJECTIVE

To investigate two patients with the hyperparathyroidism-jaw tumour (HPT-JT) syndrome and three patients with familial isolated hyperparathyroidism (FIHP), together with 31 parathyroid tumours (2 HPT-JT, 2 FIHP and 27 sporadic) for HRPT2 mutations. The HPT-JT syndrome and FIHP are autosomal dominant disorders that may be caused by abnormalities of the HRPT2 gene, located on chromosome 1q31.2. HRPT2 encodes a 531 amino acid protein, parafibromin, which interacts with human homologues of the yeast Paf1 complex.

DESIGN

Leukocyte and tumor DNA was used with HRPT2-specific primers for polymerase chain reaction amplification of the 17 exons and their splice junctions, and the DNA sequences of the polymerase chain reaction products determined.

RESULTS

Three heterozygous germline HRPT2 mutations, two in HPT-JT and one in FIHP patients, were identified. These consisted of one 1-bp duplication (745dup1bp), 1 nonsense (Arg234Stop) and 1 missense (Asp379Asn) mutation. One parathyroid tumour from an FIHP patient was demonstrated to harbour a germline deletion of 1 bp together with a somatic missense (Leu95Pro) mutation, consistent with a 'two-hit' model for hereditary cancer. The 27 sporadic benign parathyroid tumours did not harbour any HRPT2 somatic mutations. Six HRPT2 polymorphisms with allele frequencies ranging from 2% to 15% were detected.

CONCLUSIONS

Our results have identified three novel HRPT2 mutations (two germline and one somatic). The Asp379Asn mutation is likely to disrupt interaction with the human homologue of the yeast Paf1 complex, and the demonstration of combined germline and somatic HRPT2 mutations in a parathyroid tumour provide further evidence for the tumour suppressor role of the HRPT2 gene.