Multiple endocrine neoplasia 2 in Cyprus: evidence for a founder effect.

PURPOSE: Multiple endocrine neoplasia type 2 (MEN2) affects patients with RET proto-oncogene mutations. This cohort study refers to patients who were diagnosed with familial medullary thyroid carcinoma (MTC) and underwent RET genetic testing in Cyprus between years 2002 and 2017. METHODS AND PATIENTS: Forty patients underwent RET testing by Sanger sequencing of exons 10-11 and 13-16. Genotyping with STR genetic markers flanking the RET gene along with Y-chromosome genotyping and haplogroup assignment was also performed. RESULTS: RET mutations were identified in 40 patients from 11 apparently unrelated Cypriot families and two non-familial sporadic cases. Nine probands (69.2%) were heterozygous for p.Cys618Arg, one (7.7%) for p.Cys634Phe, one (7.7%) for the somatic delE632-L633 and two (15.4%) for p.Met918Thr mutations. The mean age at MTC diagnosis of patients carrying p.Cys618Arg was 36.8 ± 14.2 years. The age of pheo diagnosis ranged from 26 to 43 years and appeared simultaneously with MTC in 5/36 (13.9%) cases. The high frequency of the p.Cys618Arg mutation suggested a possible ancestral mutational event. Haplotype analysis was performed in families with and without p.Cys618Arg. Six microsatellite markers covering the RET gene and neighboring regions identified one core haplotype associated with all patients carrying p.Cys618Arg mutation. CONCLUSIONS: The mutation p.Cys618Arg is by far the most prevalent mutation in Cyprus followed by other reported mutations of variable clinical significance. The provided molecular evidence speculates p.Cys618Arg mutation as an ancestral mutation that has spread in Cyprus due to a possible founder effect.

Genetic defects of the CYP21A2 gene in girls with premature adrenarche.

OBJECTIVES: To seek evidence on the prevalence of CYP21A2 genetic defects and consequences in girls with premature adrenarche (PA). METHODS: The study included 59 girls diagnosed with PA. Direct DNA sequencing and MLPA analysis were performed to identify mutations in CYP21A2 gene. RESULTS: Twelve girls were diagnosed with non-classic congenital adrenal hyperplasia (NC-CAH) based on stimulated 17-hydroxyprogesterone (17-OHP) levels and the presence of two mutations in CYP21A2, 19 were heterozygotes. The most frequent mutations detected were the mild p.Val281Leu and p.Pro453Ser. Higher levels of mean stimulated 17-OHP were found in the carriers of the p.Val281Leu mutation. The detection rate for two CYP21A2 mutations was higher in girls with PA than in adult females with hyperandrogenemia in our studied population. A notable increased allelic frequency for the known p.Asn493Ser polymorphism was observed in the pool of the 28 girls with PA in whom no mutation was identified. CONCLUSIONS: In girls with PA, the frequency of the underlying CYP21A2 genetic defects is similar to that observed in other populations. The carrier status is likely a contributing factor in the genotype-phenotype correlation in NC-CAH. However, polymorphisms and other genes may be implicated in the clinical manifestation of the disease.

High carrier frequency of 21-hydroxylase deficiency in Cyprus.

Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency (21-OHD) is a common autosomal recessive disorder caused by mutations in the CYP21A2 gene. The carrier frequency of CYP21A2 mutations has been estimated to be 1:25 to 1:10 on the basis of newborn screening. The main objective of this study was to determine the carrier frequency in the Cypriot population of mutations in the CYP21A2 gene. Three hundred unrelated subjects (150 males and 150 females) from the general population of Cyprus were screened for mutations in the CYP21A2 gene and its promoter. The CYP21A2 genotype analysis identified six different mutants and revealed a carrier frequency of 9.83% with the mild p.Val281Leu being the most frequent (4.3%), followed by p.Qln318stop (2.5%), p.Pro453Ser (1.33%), p.Val304Met (0.83%), p.Pro482Ser (0.67%) and p.Met283Val (0.17%). The notable high CYP21A2 carrier frequency of the Cypriot population is one of the highest reported so far by genotype analysis. Knowledge of the mutational spectrum of CYP21A2 will enable to optimize mutation detection strategy for genetic diagnosis of 21-OHD not only in Cyprus, but also the greater Mediterranean region.

Genetic defects in the cyp21a2 gene in heterozygous girls with premature adrenarche and adolescent females with hyperandrogenemia.

UNLABELLED: Congenital adrenal hyperplasia (CAH) is a common autosomal recessive disorder primarily caused by mutants in the CYP21A2 gene. Heterozygosity for CYP21A2 mutations in females increases their risk of clinically manifesting hyperandrogenism and the present study was designed to seek evidence on the prevalence and consequences of heterozygous CYP21A2 mutations in children with premature adrenarche and adolescents with hyperandrogenemia. The hormonal response to ACTH was evaluated in 17 girls with clinical signs of premature adrenarche and 17 adolescent females with hyperandrogenemia, along with direct DNA sequencing and MLPA analysis for mutations in the CYP21A2 gene. The suspicion of heterozygote state was based on the median plasma 17-OHP before and 60 minutes after ACTH stimulation. All 34 patients were identified as carriers of CYP21A2 mutations. The most frequent mutations among this cohort of carriers were the mild p.V281L (52.9%), followed by p.Q318stop (20.6%), p.V304M (8.9%), p.P482S (5.9%), p.P453S (5.9%), large deletion/conversion exons 1-4 (2.9%) and large deletion/conversion exons 6-8 (2.9%). Higher values of stimulated 17-OHP levels were found in the carriers of the p.V281L mutation compared with carriers of other mutations (mean=21.9 nmol/L vs 17.0 nmol/L). This finding supports the already identified notion that carriers of the mild p.V281L are at higher risk for hyperandrogenism than carriers of severe mutations. IN CONCLUSION: a. Females with premature adrenarche and hyperandrogenemia are likely to bear heterozygous CYP21A2 mutations, therefore systematic evaluation of 17-OHP values in combination with the molecular testing of CYP21A2 gene is beneficial, b. carriers of the mild p.V281L, are at higher risk of androgen excess compared to carriers of other types of mutations.

Guidelines for the genetic diagnosis of hereditary recurrent fevers.

Hereditary recurrent fevers (HRFs) are a group of monogenic autoinflammatory diseases characterised by recurrent bouts of fever and serosal inflammation that are caused by pathogenic variants in genes important for the regulation of innate immunity. Discovery of the molecular defects responsible for these diseases has initiated genetic diagnostics in many countries around the world, including the Middle East, Europe, USA, Japan and Australia. However, diverse testing methods and reporting practices are employed and there is a clear need for consensus guidelines for HRF genetic testing. Draft guidelines were prepared based on current practice deduced from previous HRF external quality assurance schemes and data from the literature. The draft document was disseminated through the European Molecular Genetics Quality Network for broader consultation and amendment. A workshop was held in Bruges (Belgium) on 18 and 19 September 2011 to ratify the draft and obtain a final consensus document. An agreed set of best practice guidelines was proposed for genetic diagnostic testing of HRFs, for reporting the genetic results and for defining their clinical significance.

RET proto-oncogene mutations are restricted to codon 618 in Cypriot families with multiple endocrine neoplasia 2.

BACKGROUND: RET germline mutations predispose to the development of inherited cancer syndrome multiple endocrine neoplasia type 2 (MEN2). Several variants of the RET proto-oncogene including G691S and S904S have been suggested to act as genetic modifiers at the age of onset ofMEN2. AIM: The aim of this study is to characterize clinically and molecularly 7 Cypriot patients with familial medullary thyroid carcinoma (FMTC) and 1 with MEN2A and also to determine the allelic frequencies of the RET variants G691S and S904S. SUBJECTS AND METHODS: Seven probands from FMTC families and 1 from MEN2A were screened for the presence of RET mutations and the G691S and S904S variants. Additionally, 226 healthy Cypriots, who served as controls were analysed in an attempt to compare the frequencies of G691S and S904S RET variants to those observed in the 8 patients. RESULTS: The clinical diagnosis of the probands was based on clinical presentation and supported with biochemical findings. The germline C618R mutation of exon 10 was identified in all 8 probands and in 15 relatives from 7 different families. No significant difference in the G691S/S904S variants allele frequencies between patients (4/16 or 25%) and controls (124/452 or 27.4%) was found. CONCLUSIONS: Mutational screening of the RET gene identified a common mutation (C618R) in all 8 (7 FMTC and 1 MEN2A) unrelated Cypriot patients which may be explained by a founder effect. Additionally, no association of the G691S/S904S variants was linked with the disease.

The IVS1-2A>G mutation in the SRD5A2 gene predominates in Cypriot patients with 5α reductase deficiency.

BACKGROUND: 5α steroid reductase deficiency (5αSRD) is an autosomal recessive enzymatic deficiency and mutations in the 5α steroid reductase type 2 gene (SRD5A2) result in male pseudohermaphrodism caused by decreased dihydrotestosterone (DHT) synthesis. AIM: To identify the specific mutations of the SRD5A2 gene in Cypriot patients with 5αSRD. SUBJECTS AND METHODS: Five unrelated patients with 46,XY karyotype were examined. Four of them were born with ambiguous genitalia and 1 patient, who was raised as girl, presented with primary amenorrhea. The hCG test was informative (elevated testosterone/DHT) of 5αSRD in 3 out of 4 subjects. Sequencing of the SRD5A2 gene was completed for all patients. Genomic DNA was also isolated from a total of 204 healthy unrelated Cypriot subjects. Screening for the IVS1-2A>G mutation was performed by using direct sequencing and restriction enzyme analysis. RESULTS: The IVS1-2A>G was identified in homozygosity in 3 patients and in a compound heterozygote state in the other 2 patients, in combination with p.P181L and p.R171S in exon 3, respectively. The carrier frequency in the Cypriot population for the IVS1-2A>G mutation was estimated to be 0.98% or 2 in 204. CONCLUSIONS: The same IVS1-2A>G mutation in the SRD5A2 gene seems to characterize all Cypriot patients with 5αSRD diagnosed so far. Furthermore this relatively rare genetic defect, which has only been reported previously in a single case in the Eastern Mediterranean region, is very likely to be the result of a founder effect.

RNA interference and the use of small interfering RNA to study gene function in mammalian systems.

In the past 2 years, extraordinary developments in RNA interference (RNAi)-based methodologies have seen small interfering RNAs (siRNA) become the method of choice for researchers wishing to target specific genes for silencing. In this review, an historic overview of the biochemistry of the RNAi pathway is described together with the latest advances in the RNAi field. Particular emphasis is given to strategies by which siRNAs are used to study mammalian gene function. In this regard, the use of plasmid-based and viral vector-based systems to mediate long-term RNAi in vitro and in vivo are described. However, recent work has shown that non-specific silencing effects and activation of the interferon response may occur following the use of some siRNA and delivery vector combinations. Future goals must therefore be to understand the mechanisms by which siRNA delivery leads to unwanted gene silencing effects in cells and, in this way, RNAi technology can reach its tremendous potential as a scientific tool and ultimately be used for therapeutic purposes.

Hammerhead ribozymes reduce central nervous system (CNS)-derived neuronal nitric oxide synthase messenger RNA in a human cell line.

Catalytic RNA molecules (ribozymes) have been widely used specifically to suppress gene expression. Neuronal nitric oxide synthase (nNOS) is an important molecule involved in normal central nervous system function (e.g. vasodilation, neurotransmission.) and disease (e.g. oxidative stress). This report is an investigation of the hammerhead ribozyme function and potential in the central nervous system using nNOS as a model. Two antisense hammerhead ribozymes, nNOS-RZ1 and nNOS-RZ2, were designed and constructed against nNOS messenger RNA (mRNA). In vitro (cell-free) experiments demonstrated the ability of both ribozymes to cleave nNOS RNA targets. Ribozyme-mediated reduction of the endogenous nNOS mRNA in human TGW-I-nu neuroblastoma cells was demonstrated by plasmid- and adenovirus-mediated transfections. These results may form the basis for studying neuronal gene expression and for designing RNA-directed therapeutic strategies for neurological diseases that involve oxidative stress.

Ribozyme and peptide-nucleic acid-based gene therapy.

The recent discovery that RNA can act as a catalyst, apart from carrying genetic information, has given a new dimension to the field of gene therapy and has come to act synergistically with antisense technology. Ribozymes can be used to down-regulate (by RNA cleavage) or repair (by RNA trans-splicing) unwanted gene expression involved in disease. Hammerhead ribozymes have been used extensively to down-regulate gene expression in many diseases such as viral infections and cancer. Group I intron ribozymes on the other hand, have only been tried to repair inherited mutations but hold great promise for the future. Peptide nucleic acids (PNAs) technology is another new technology, which is currently been tried to block gene or RNA function. Gene therapy protocols need significant improvements in order to be used routinely in patients and hopefully, these new players should prove valuable to identifying new therapies for several untreated diseases.

Potential therapy paradigms for Marfan syndrome.

Marfan syndrome is the most common genetic disorder of the connective tissue with an estimated prevalence of 1:10,000. The disease is characterised by manifestations in the cardiovascular, skeletal and ocular systems. The most severe manifestations are those of the cardiovascular system: mitral valve prolapse and dilation of the aortic root, which may progress to aortic dissection, a common cause of mortality in patients. Marfan syndrome is a dominant genetic disorder caused by mutations in the gene coding for fibrillin-1, the FBN1 gene. Fibrillin, a 347 kDa glycoprotein, is found in most connective tissues and is a major component of the extracellular microfibrils. More than 100 different FBN1 mutations have been identified in individuals with Marfan syndrome, the majority of which are unique missense point mutations. Evidence suggests a dominant-negative mechanism of pathogenesis for the disorder, that is, the presence of the mutant fibrillin molecule interferes with the function of the normal protein. Therapies for dominant disorders such as Marfan syndrome (MFS) are likely to require both suppression of the disease allele expression and maintenance of expression of its wild-type counterpart. Thus, dominant genetic disorders present a unique therapeutic challenge. One approach to developing a therapy would be to use catalytic nucleic acid molecules. Antisense catalytic RNAs, or ribozymes, have been widely used to down-regulate or repair targeted gene expression respectively through the cleavage or trans-splicing of messenger RNA. Similarly, antisense DNA molecules or DNAzymes have been shown to be capable of cleaving target RNA molecules in a highly specific manner. This review will discuss the potential of catalytic nucleic acid molecules as therapeutic agents for MFS.

Towards an RNA-based therapy for Marfan syndrome.

Dominant genetic disorders, particularly those due to a mutant protein exerting a dominant-negative effect, present a unique challenge for gene therapy. Unlike recessive disorders, where expression of a wild-type gene is likely to be sufficient to ameliorate disease pathology, therapies for dominant disorders are likely to require suppression of the disease allele while maintaining expression of its wild-type counterpart. Marfan syndrome, the most common genetic disorder of the connective tissue, is caused by mutant fibrillin 1 protein exerting a dominant-negative effect. Antisense hammerhead ribozymes--small catalytic RNAs capable of targeting and cleaving specific RNA molecules--appear to offer promise in the development of a therapy for Marfan syndrome.

Hammerhead ribozymes targeted to the FBN1 mRNA can discriminate a single base mismatch between ribozyme and target.

Hammerhead ribozymes are catalytic RNA molecules that can act in trans, with ribozyme and substrate being two different oligoribonucleotides with regions of complementarity. Mutations in the gene for fibrillin-1 (FBN1) cause Marfan syndrome. The majority of mutations are single-base changes, many of which exert their effect via a dominant-negative mechanism. Previously we have shown that an antisense hammerhead ribozyme, targeted to the FBN1 mRNA can reduce deposition of fibrillin to the extracellular matrix of cultured fibroblasts, suggesting it may be possible to utilize ribozymes to down regulate the production of mutant protein and thus restore normal fibrillin function. This might be achieved by the mutation creating a ribozyme cleavage site that is not present in the normal allele, however this is likely to limit the number of mutations that could be targeted. Alternatively, it might be possible to target the mutant allele via the ribozyme binding arms. To determine the potential of ribozymes to preferentially target mutant FBN1 alleles via the latter approach, the effect of mismatches in helix I of a hammerhead ribozyme, on the cleavage of fibrillin (FBN1) mRNA was investigated. A single base mismatch significantly reduced ribozyme cleavage efficiency both in vitro and in vivo. The discrimination between fully-matched and mismatched ribozyme varied with the length of helix I, with the discrimination being more pronounced in ribozymes with a shorter helix. These data suggest that it should be possible to design hammerhead ribozymes that can discriminate between closely related (mutant and normal) target RNAs varying in as little as a single nucleotide, even if the mutation does not create a ribozyme cleavage site.

Ribozymes as therapeutic tools for genetic disease.

The discovery that RNA can act as a biological catalyst, as well as a genetic molecule, indicated that there was a time when biological reactions were catalysed in the absence of protein-based enzymes. It also provided the platform to develop those catalytic RNA molecules, called ribozymes, as trans -acting tools for RNA manipulation. Viral diseases or diseases due to genetic lesions could be targeted therapeutically through ribozymes, provided that the sequence of the genetic information involved in the disease is known. The hammerhead ribozyme, one of the smallest ribozymes identified, is able to induce site-specific cleavage of RNA, with ribozyme and substrate being two different oligoribonucleotides with regions of complementarity. Its ability to down-regulate gene expression through RNA cleavage makes the hammerhead ribozyme a candidate for genetic therapy. This could be particularly useful for dominant genetic diseases by down-regulating the expression of mutant alleles. The group I intron ribozyme, on the other hand, is capable of site-specific RNA trans -splicing. It can be engineered to replace part of an RNA with sequence attached to its 3' end. Such application may have importance in the repair of mutant mRNA molecules giving rise to genetic diseases. However, to achieve successful ribozyme-mediated RNA-directed therapy, several parameters including ribozyme stability, activity and efficient delivery must be considered. Ribozymes are promising genetic therapy agents and should, in the future, play an important role in designing strategies for the therapy of genetic diseases.

Ribozyme-mediated trans-splicing of a trinucleotide repeat.

Trinucleotide repeat expansions (TREs) are a recently described class of mutations characterized by a change in the size of the genomic fragment due to amplification of the repeated unit. A number of diseases have been attributed to TRE, including Huntington disease and myotonic dystrophy (DM), but attempts at genetic therapy have yet to prove successful. A potential therapeutic approach would be to repair the expanded repeat using the trans-splicing ability of group I intron ribozymes. We have used DM as a model to test this hypothesis. A group I intron ribozyme (DMPK-RZ1) was designed to modify the TRE at the 3' end of the human myotonic dystrophy protein kinase (DMPK) transcripts. DMPK-RZ1 was shown to ligate a small DMPK mRNA fragment, contained within the ribozyme, to a simple DMPK-target RNA in vitro. It also modified a larger target transcript, leading to replacement of twelve repeats with five repeats, both in vitro and in mammalian cells. Finally, this ribozyme successfully replaced the 3' end of endogenous DMPK mRNA in fibroblasts with a different 3' region. Ribozyme-mediated RNA repair may thus form a novel therapeutic strategy for diseases associated with repeat expansions.

Delivery of a hammerhead ribozyme specifically down-regulates the production of fibrillin-1 by cultured dermal fibroblasts.

The hammerhead ribozyme is a small catalytic RNA molecule. Potential hammerhead ribozymes that possess a catalytic domain and flanking sequence complementary to a target mRNA can cleave in trans at a putative cleavage site within the target molecule. We have investigated the potential of hammerhead ribozymes to down-regulate the product of the fibrillin-1 gene (FBN1). Fibrillin is a 347 kDa glycoprotein that is a major constituent of the elastin-associated microfibrils. Mutations in the FBN1 gene are responsible for Marfan syndrome (MFS), a common systemic disorder of the connective tissue. Many FBN1 mutations responsible for MFS appear to act in a dominant-negative fashion, raising the possibility that reduction of the amount of product from the mutant FBN1 allele might be a valid therapeutic approach for MFS. A trans-acting hammerhead ribozyme (FBN1-RZ1) targeted to the 5' end of the human FBN1 mRNA has been designed and synthesized, and shown to cleave its target efficiently in vitro. FBN1-RZ1 cleavage is magnesium dependent and efficient at both 37 and 50 degrees C. Delivery of the FBN1-RZ1 ribozyme into cultured dermal fibroblasts, by receptor-mediated endocytosis of a ribozyme-transferrin-polylysine complex, specifically reduces both cellular FBN1 mRNA and the deposition of fibrillin in the extracellular matrix. These results suggest that the use of hammerhead ribozymes is a valid approach to the study of fibrillin gene expression and possibly to the development of a therapeutic approach to MFS.

Preimplantation genetic diagnosis in Marfan syndrome.

The in vitro fertilization technology coupled with the ability to amplify DNA from a single cell has been used for the preimplantation genetic diagnosis of Marfan syndrome. An intragenic FBN1 gene marker has been used to track the inheritance of this disorder in a family. Marker genotyping was established following two rounds of amplification. Whenever possible, two blastomeres were separately assayed per embryo. The transfer of five embryos resulted in a singleton pregnancy and the birth of a full-term male infant.

The detection of herpesviral DNA in aqueous fluid samples from patients with Fuchs' heterochromic cyclitis.

Members of the herpesvirus family have been found in association with a variety of intraocular inflammatory conditions. The aetiology and pathogenic mechanisms underlying the specific uveitis entity Fuchs' heterochromic cyclitis (FHC) have yet to be determined. This study investigates the presence of specific herpesviral DNA in samples of aqueous fluid from patients with FHC. Aqueous humour was obtained from 40 patients undergoing cataract surgery, 20 patients with a clinical diagnosis of FHC and 20 patients with senile cataract who acted as controls. Each sample was tested for the presence of Epstein-Barr virus (EBV), cytomegalovirus (CMV), herpes simplex virus (HSV) and varicella-zoster virus (VZV) DNA after initial amplification with virus specific primers using the polymerase chain reaction (PCR). Herpesviral DNA could not be detected in any of the aqueous samples from the FHC patients. Although a viral aetiology is unlikely, this study cannot exclude the possibility that a virus may be the initiating factor in the development of FHC or that virus may be sequestered in different ocular tissues. Control patients also showed no significant carriage of herpesvirus in their aqueous humour implying that detection of any herpesviral DNA in aqueous samples may be clinically relevant.