Female-Specific Association Between Variants on Chromosome 9 and Self-Reported Diagnosis of Irritable Bowel Syndrome.

BACKGROUND & AIMS: Genetic factors are believed to affect risk for irritable bowel syndrome (IBS), but there have been no sufficiently powered and adequately sized studies. To identify DNA variants associated with IBS risk, we performed a genome-wide association study (GWAS) of the large UK Biobank population-based cohort, which includes genotype and health data from 500,000 participants. METHODS: We studied 7,287,191 high-quality single nucleotide polymorphisms in individuals who self-reported a doctor's diagnosis of IBS (cases; n = 9576) compared to the remainder of the cohort (controls; n = 336,499) (mean age of study subjects, 40-69 years). Genome-wide significant findings were further investigated in 2045 patients with IBS from tertiary centers and 7955 population controls from Europe and the United States, and a small general population sample from Sweden (n = 249). Functional annotation of GWAS results was carried out by integrating data from multiple biorepositories to obtain biological insights from the observed associations. RESULTS: We identified a genome-wide significant association on chromosome 9q31.2 (single nucleotide polymorphism rs10512344; P = 3.57 × 10-8) in a region previously linked to age at menarche, and 13 additional loci of suggestive significance (P < 5.0×10-6). Sex-stratified analyses revealed that the variants at 9q31.2 affect risk of IBS in women only (P = 4.29 × 10-10 in UK Biobank) and also associate with constipation-predominant IBS in women (P = .015 in the tertiary cohort) and harder stools in women (P = .0012 in the population-based sample). Functional annotation of the 9q31.2 locus identified 8 candidate genes, including the elongator complex protein 1 gene (ELP1 or IKBKAP), which is mutated in patients with familial dysautonomia. CONCLUSIONS: In a sufficiently powered GWAS of IBS, we associated variants at the locus 9q31.2 with risk of IBS in women. This observation may provide additional rationale for investigating the role of sex hormones and autonomic dysfunction in IBS.

Functional variants in the sucrase-isomaltase gene associate with increased risk of irritable bowel syndrome.

OBJECTIVE: IBS is a common gut disorder of uncertain pathogenesis. Among other factors, genetics and certain foods are proposed to contribute. Congenital sucrase-isomaltase deficiency (CSID) is a rare genetic form of disaccharide malabsorption characterised by diarrhoea, abdominal pain and bloating, which are features common to IBS. We tested sucrase-isomaltase (SI) gene variants for their potential relevance in IBS. DESIGN: We sequenced SI exons in seven familial cases, and screened four CSID mutations (p.Val557Gly, p.Gly1073Asp, p.Arg1124Ter and p.Phe1745Cys) and a common SI coding polymorphism (p.Val15Phe) in a multicentre cohort of 1887 cases and controls. We studied the effect of the 15Val to 15Phe substitution on SI function in vitro. We analysed p.Val15Phe genotype in relation to IBS status, stool frequency and faecal microbiota composition in 250 individuals from the general population. RESULTS: CSID mutations were more common in patients than asymptomatic controls (p=0.074; OR=1.84) and Exome Aggregation Consortium reference sequenced individuals (p=0.020; OR=1.57). 15Phe was detected in 6/7 sequenced familial cases, and increased IBS risk in case-control and population-based cohorts, with best evidence for diarrhoea phenotypes (combined p=0.00012; OR=1.36). In the population-based sample, 15Phe allele dosage correlated with stool frequency (p=0.026) and Parabacteroides faecal microbiota abundance (p=0.0024). The SI protein with 15Phe exhibited 35% reduced enzymatic activity in vitro compared with 15Val (p<0.05). CONCLUSIONS: SI gene variants coding for disaccharidases with defective or reduced enzymatic activity predispose to IBS. This may help the identification of individuals at risk, and contribute to personalising treatment options in a subset of patients.

Increased Prevalence of Rare Sucrase-isomaltase Pathogenic Variants in Irritable Bowel Syndrome Patients.

Patients with irritable bowel syndrome (IBS) often associate their symptoms to certain foods. In congenital sucrase-isomaltase deficiency (CSID), recessive mutations in the SI gene (coding for the disaccharidase digesting sucrose and 60% of dietary starch)1 cause clinical features of IBS through colonic accumulation of undigested carbohydrates, triggering bowel symptoms.2 Hence, in a previous study,3 we hypothesized that CSID variants reducing SI enzymatic activity may contribute to development of IBS symptoms. We detected association with increased risk of IBS for 4 rare loss-of-function variants typically found in (homozygous) CSID patients, because carriers (heterozygous) of these rare variants were more common in patients than in controls.1,4 Through a 2-step computational and experimental strategy, the present study aimed to determine whether other (dys-)functional SI variants are associated with risk of IBS in addition to known CSID mutations. We first aimed to identify all SI rare pathogenic variants (SI-RPVs) on the basis of integrated Mendelian Clinically Applicable Pathogenicity (M-CAP) and Combined Annotation Dependent Depletion (CADD) predictive (clinically relevant) scores; next, we inspected genotype data currently available for 2207 IBS patients from a large ongoing project to compare SI-RPV case frequencies with ethnically matched population frequencies from the Exome Aggregation Consortium (ExAC).

Chronic constipation diagnosis and treatment evaluation: the "CHRO.CO.DI.T.E." study.

BACKGROUND: According to Rome criteria, chronic constipation (CC) includes functional constipation (FC) and irritable bowel syndrome with constipation (IBS-C). Some patients do not meet these criteria (No Rome Constipation, NRC). The aim of the study was is to evaluate the various clinical presentation and management of FC, IBS-C and NRC in Italy. METHODS: During a 2-month period, 52 Italian gastroenterologists recorded clinical data of FC, IBS-C and NRC patients, using Bristol scale, PAC-SYM and PAC-QoL questionnaires. In addition, gastroenterologists were also asked to record whether the patients were clinically assessed for CC for the first time or were in follow up. Diagnostic tests and prescribed therapies were also recorded. RESULTS: Eight hundred seventy-eight consecutive CC patients (706 F) were enrolled (FC 62.5%, IBS-C 31.3%, NRC 6.2%). PAC-SYM and PAC-QoL scores were higher in IBS-C than in FC and NRC. 49.5% were at their first gastroenterological evaluation for CC. In 48.5% CC duration was longer than 10 years. A specialist consultation was requested in 31.6%, more frequently in IBS-C than in NRC. Digital rectal examination was performed in only 56.4%. Diagnostic tests were prescribed to 80.0%. Faecal calprotectin, thyroid tests, celiac serology, breath tests were more frequently suggested in IBS-C and anorectal manometry in FC. More than 90% had at least one treatment suggested on chronic constipation, most frequently dietary changes, macrogol and fibers. Antispasmodics and psychotherapy were more frequently prescribed in IBS-C, prucalopride and pelvic floor rehabilitation in FC. CONCLUSIONS: Patients with IBS-C reported more severe symptoms and worse quality of life than FC and NRC. Digital rectal examination was often not performed but at least one diagnostic test was prescribed to most patients. Colonoscopy and blood tests were the "first line" diagnostic tools. Macrogol was the most prescribed laxative, and prucalopride and pelvic floor rehabilitation represented a "second line" approach. Diagnostic tests and prescribed therapies increased by increasing CC severity.

Delayed gastric emptying does not normalize after gluten withdrawal in adult celiac disease.

Objective Delayed gastric emptying has been frequently detected in patients with untreated celiac disease. According to several studies, gluten withdrawal showed to be effective in normalizing the gastric emptying rate. The aim of this study was to evaluate the gastric emptying rate of solids in patients with celiac disease before and after a gluten-free diet. Methods Twelve adult patients with celiac disease (age range 20-57 years) and 30 healthy controls (age range 30-54 years) underwent a (13)C-octanoic acid breath test to measure gastric emptying. Half emptying time (t1/2) and lag phase (tlag) were calculated. After at least 12 months of a gluten-free diet, celiac patients underwent a new (13)C-octanoic acid breath test. A symptom score was utilized to detect dyspeptic and malabsorption symptoms in all the patients. Results The gastric motility parameters, t1/2 and tlag, were significantly longer in patients than in controls. On a gluten-free diet, surprisingly, the gastric emptying did not normalize despite an improvement of symptom score. No significant correlation between abnormal gastric emptying and specific symptom patterns, anthropometric parameters or severity of histological damage was found. Conclusions This finding supports the hypothesis that gluten-driven mucosal inflammation might determine motor abnormalities by affecting smooth muscle contractility or impairing gut hormone function. The persistence of these abnormalities on a gluten free diet suggests the presence of a persistent low-grade mucosal inflammation with a permanent perturbation of the neuro-immunomodulatory regulation.

Loss-of-function of the voltage-gated sodium channel NaV1.5 (channelopathies) in patients with irritable bowel syndrome.

BACKGROUND & AIMS: SCN5A encodes the α-subunit of the voltage-gated sodium channel NaV1.5. Many patients with cardiac arrhythmias caused by mutations in SCN5A also have symptoms of irritable bowel syndrome (IBS). We investigated whether patients with IBS have SCN5A variants that affect the function of NaV1.5. METHODS: We performed genotype analysis of SCN5A in 584 persons with IBS and 1380 without IBS (controls). Mutant forms of SCN5A were expressed in human embryonic kidney-293 cells, and functions were assessed by voltage clamp analysis. A genome-wide association study was analyzed for an association signal for the SCN5A gene, and replicated in 1745 patients in 4 independent cohorts of IBS patients and controls. RESULTS: Missense mutations were found in SCN5A in 13 of 584 patients (2.2%, probands). Diarrhea-predominant IBS was the most prevalent form of IBS in the overall study population (25%). However, a greater percentage of individuals with SCN5A mutations had constipation-predominant IBS (31%) than diarrhea-predominant IBS (10%; P < .05). Electrophysiologic analysis showed that 10 of 13 detected mutations disrupted NaV1.5 function (9 loss-of-function and 1 gain-of-function function). The p. A997T-NaV1.5 had the greatest effect in reducing NaV1.5 function. Incubation of cells that expressed this variant with mexiletine restored their sodium current and administration of mexiletine to 1 carrier of this mutation (who had constipation-predominant IBS) normalized their bowel habits. In the genome-wide association study and 4 replicated studies, the SCN5A locus was strongly associated with IBS. CONCLUSIONS: About 2% of patients with IBS carry mutations in SCN5A. Most of these are loss-of-function mutations that disrupt NaV1.5 channel function. These findings provide a new pathogenic mechanism for IBS and possible treatment options.

Ustekinumab in the Treatment of Inflammatory Bowel Diseases: Evolving Paradigms.

Inflammatory bowel diseases, comprising Crohn's disease (CD) and ulcerative colitis (UC), are chronic, relapsing, and remitting immune-mediated inflammatory diseases affecting the gastrointestinal tract. Ustekinumab (UST) is a monoclonal antibody that blocks the p40 subunit of the anti-interleukin (IL) 12/23. Pivotal trials (CERTIFI and UNITI-IM for CD, UNIFI for UC) established the efficacy of UST for the induction and maintenance of remission in both CD and UC, with the most favorable results in naïve patients to biologics. In recent years, a wealth of 'real-world' data has emerged supporting positive clinical, endoscopic, and histological outcomes in patients treated with UST, as well as reassuring safety data. More recently, the results of the first head-to-head trials of UST and tumor necrosis factor (TNF) antagonists were reported. Moreover, a number of studies exploring the role of UST in specific clinical settings, such as perianal CD, postoperative complications and recurrence, extraintestinal manifestations, chronic antibiotic-refractory pouchitis, and pregnancy, were reported. This review explores the results reported to date on UST, including those from pivotal trials, real-world data, and emerging studies regarding therapeutic drug monitoring and immunogenicity. The safety profile of UST was also reviewed.

Impact of a Symbiotic Mixture on Moderate-to-severe Diverticular Disease of the Colon.

BACKGROUND: Microbial imbalance is thought to play a role in the pathogenesis of Diverticular Disease (DD). OBJECTIVE: We aimed to assess the efficacy of a symbiotic mixture (Prolactis GG Plus®) in the treatment of moderate to severe DD, scored according to the Diverticular Inflammation and Complication Assessment (DICA) classification. METHODS: A retrospective study was conducted enrolling the following patients: at the first diagnosis of DD; in whom DD was diagnosed with colonoscopy and scored according to DICA classification; treated with Prolactis GG Plus® two times/daily for 2 consecutive months; in whom the severity of the abdominal pain was scored with a 10-points visual-analogue scale (VAS) at baseline and the end of follow-up; in whom fecal calprotectin (FC) was assessed at baseline and the end of follow-up as µg/g. RESULTS: Twenty-four patients were identified (10 males, 14 females; 16 as DICA 2, and 8 as DICA 3). Prolactis GG Plus® decreased the severity of abdominal pain both in DICA 2 (p =0.02) and DICA 3 patients (p =0.01), while FC decreased significantly in DICA 2 (p <0.02) but not in DICA 3 (p =0.123) patients. Acute diverticulitis occurred during the follow-up in two DICA 3 patients but none DICA 2 patients. Add-on therapy was required by eight DICA 2 (50%) and six DICA 3 patients (75%). CONCLUSION: In newly diagnosed patients with DD, the symbiotic mixture Prolactis GG Plus® can be a potential treatment for moderate (DICA 2) DD as a single treatment.

Rifaximin in diverticulosis and diverticular disease: a national survey among Italian gastroenterologists and general practitioners.

The management of patients with diverticular disease remains challenging. The aim of this national survey was to assess how gastroenterologists and general practitioners use rifaximin to manage diverticulosis and diverticular disease. Members of the Italian Association of Hospital Gastroenterologists and Endoscopists (AIGO) and the Italian Federation of General Practitioners (FIMMG) were invited to complete a 39-item online survey concerning the use of rifaximin in five clinical settings: (1) diverticulosis; (2) reducing symptoms in symptomatic uncomplicated diverticular disease; (3) reducing the occurrence of diverticulitis in patients with symptomatic uncomplicated diverticular disease (primary prevention); (4) reducing the recurrence of diverticulitis in patients with previous attacks of diverticulitis (secondary prevention); (5) treatment of uncomplicated acute diverticulitis. A total of 1094 physicians completed the survey. Overall, 25.1%, 83.5%, 68%, 74.2%, and 63% of physicians prescribed rifaximin for the clinical settings 1, 2, 3, 4, and 5, respectively. In each clinical setting, the dosage of rifaximin most frequently used was 800 mg/day, the most common duration of therapy was 7 days, and the cyclic administration of treatment (expressed in months) most frequently used was > 24 months. These results highlight that a reappraisal of the use of rifaximin in patients with diverticulosis and diverticular disease is required to reduce the gap between the evidence available and the daily clinical practice, optimizing also the use of healthcare resources.

New Perspectives on Lactose Malabsorption, Celiac Disease and Related Disorders.

Lactose malabsorption (LM) is caused by the incomplete hydrolysis of lactose due to lactase deficiency [...].

Misinterpreting Diarrhea-Predominant Irritable Bowel Syndrome and Functional Diarrhea: Pathophysiological Highlights.

Irritable bowel syndrome with predominant diarrhea (IBS-D) and functional diarrhea (FD) are disorders of gut-brain interaction characterized by recurring symptoms which have a serious impact on the patient's quality of life. Their pathophysiology is far from being completely understood. In IBS-D growing evidence suggests that bile acid malabsorption (BAM) could be present in up to 30% of patients. Microscopic colitis (MC) is a well-known cause of watery diarrhea and some patients, at first, can be diagnosed as IBS-D or FD. Both BAM and MC are often responsible for the lack of response to conventional treatments in patients labelled as "refractory". Moreover, because BAM and MC are not mutually exclusive, and can be found in the same patient, they should always be considered in the diagnostic workout when a specific treatment for BAM or MC is unsatisfactory. In the present review the possible shared pathogenetic mechanisms between BAM and MC are discussed highlighting how MC can induce a secondary BAM. Moreover, a brief overview of the current literature regarding the prevalence of their association is provided.

Real-world efficacy and safety of vedolizumab in managing ulcerative colitis versus Crohn's disease: results from an Italian multicenter study.

BACKGROUND: Vedolizumab (VDZ) can be used to treat refractory ulcerative colitis (UC) and Crohn's disease (CD). We assessed whether there are differences in treating UC vs CD with VDZ. RESEARCH DESIGN AND METHODS: Mayo score in UC and the Harvey-Bradshaw Index (HBI) in CD scored the clinical activity. Achievement and maintenance of clinical remission during the follow-up, and safety were the primary endpoints. RESULTS: 729 patients (475 with UC and 254 with CD), median follow-up of 18 (IQR 6-36) months, were enrolled. Clinical remission at the 6th month of treatment was achieved in 488 (66.9%) patients (74.4% in CD vs 62.9% in UC, p<0.002) while, during the follow-up, no difference was found (81.5% in the UC group and 81.5% pts in the CD group; p=0.537). The clinical remission at the 6th month of treatment (p=0.001) and being naïve to biologics (p<0.0001) were significantly associated with prolonged clinical remission. The clinical response was significantly higher in UC (90.1%) vs CD (84.3%) (p=0.023), and surgery occurred more frequently in CD (1.9% in UC vs 5.1% in CD, p=0.016). CONCLUSION: We found differences when using VDZ in UC vs CD in real life. These parameters can help the physician predict this drug's longterm efficacy.

Use of tofacitinib as first or second-line therapy is associated with better outcomes in patients with ulcerative colitis: data from a real-world study.

BACKGROUND: Data regarding the real-world (RW) use of tofacitinib (TOF) in patients with ulcerative colitis (UC) are limited. We aimed to investigate TOF's RW efficacy and safety in Italian UC patients. RESEARCH DESIGN AND METHODS: A retrospective assessment of clinical and endoscopic activity was performed according to the Mayo score. The primary endpoints were to evaluate the effectiveness and safety of TOF. RESULTS: We enrolled 166 patients with a median follow-up of 24 (IQR 8-36) weeks. Clinical remission was achieved in 61/166 (36.7%) and 75/166 (45.2%) patients at 8-week and 24-week follow-ups, respectively. The optimization was requested in 27 (16.3%) patients. Clinical remission was achieved more frequently when TOF was used as a first/second line rather than a third/fourth line treatment (p = 0.007). Mucosal healing was reported in 46% of patients at the median follow-up time. Colectomy occurred in 8 (4.8%) patients. Adverse events occurred in 12 (5.4%) patients and severe in 3 (1.8%). One case of simple Herpes Zoster and one of renal vein thrombosis were recorded. CONCLUSIONS: Our RW data confirm that TOF is effective and safe in UC patients. It performs remarkably better when used as the first/second line of treatment.

Upper Gastrointestinal Endoscopy Quality in Italy: A Nationwide Study.

BACKGROUND AND AIMS: International guidelines advise improving esophagogastroduodenoscopy (EGD) quality in Western countries, where gastric cancer is still diagnosed in advanced stages. This nationwide study investigated some indicators for the quality of EGD performed in endoscopic centers in Italy. METHODS: Clinical, endoscopic, and procedural data of consecutive EGDs performed in one month in the participating centers were reviewed and collected in a specific database. Some quality indicators before and during endoscopic procedures were evaluated. RESULTS: A total of 3,219 EGDs performed by 172 endoscopists in 28 centers were reviewed. Data found that some relevant information (family history for GI cancer, smoking habit, use of proton pump inhibitors) were not collected before endoscopy in 58.5-80.7% of patients. Pre-endoscopic preparation for gastric cleaning was routinely performed in only 2 (7.1%) centers. Regarding the procedure, sedation was not performed in 17.6% of patients, and virtual chromoendoscopy was frequently (>75%) used in only one (3.6%) center. An adequate sampling of the gastric mucosa (i.e., antral and gastric body specimens) was heterogeneously performed, and it was routinely performed only by 23% of endoscopists, and in 14.3% centers. CONCLUSIONS: Our analysis showed that the quality of EGD performed in clinical practice in Italy deserves to be urgently improved in different aspects.

Effects of Prokinetics on the Digestive Tract.

BACKGROUND: Functional gastrointestinal disorders account for at least a third of visits to gastroenterology clinics. Despite pathophysiological complexity, impaired gut motility may be frequently present in these disorders. INTRODUCTION: Prokinetics are a class of drugs that promote gastrointestinal motility, accelerate transit, and potentially improve digestive symptoms. Several prokinetic agents with a great variety of mechanisms of action are available. AIM: The purpose of this paper is to update our current knowledge about the efficacy and safety of prokinetics. METHODS: A literature search on efficacy and safety of prokinetics was carried out using the online databases of Pubmed, Medline, and Cochrane. RESULTS: Based on the action of different receptors, prokinetics mainly comprise dopamine antagonists, 5HT4 agonists, motilin agonists, ghrelin agonists, and cholinergic agonists. Prokinetics have the potential to improve motility function in all segments of the digestive tract, from the esophagus to the colon. In particular, drug international agencies have approved antidopaminergic metoclopramide for the treatment of gastroparesis and serotoninergic prucalopride for chronic constipation not responsive to traditional laxatives. Arrhythmias by QT prolongation and galactorrhea by prolactin stimulation are the more frequent side effects related to prokinetics use. CONCLUSION: Old and new prokinetics are effective in ameliorating digestive motility disorders and related symptoms and are widely prescribed. Special attention should be paid to the potential adverse events of these agents.

Lactose Malabsorption and Presumed Related Disorders: A Review of Current Evidence.

BACKGROUND: Lactose malabsorption (LM) is a frequent clinical problem associated with several digestive and extra-digestive diseases. The aim of this manuscript was to clarify the real clinical impact of LM on these disorders. METHODS: A literature search for digestive and extra-digestive disorders related to LM was carried out using PubMed, Medline and Cochrane. RESULTS: A transient lactase deficiency is present in celiac disease (CD) on a normal diet. The persistence of symptoms in CD on a gluten-free diet may be instead, in part, attributed to a primary LM. Similar circumstances are present in inflammatory bowel diseases (IBD), in which LM can be responsible for a part of persistent symptoms in IBD on clinical remission. LM and irritable bowel syndrome (IBS) are instead independent conditions. On the other hand, a lactose-restricted diet may be useful for some IBS patients. A reduced lactose intake can lead to low bone mass and limited risk of fragility fractures. Finally, the absorption of levothyroxine could be conditioned by LM. CONCLUSIONS: LM can be responsible for persistent symptoms in CD and IBD. The association with IBS seems to be casual. Bone mass and levothyroxine absorption can be affected by LM.

Translational Gap between Guidelines and Clinical Medicine: The Viewpoint of Italian General Practitioners in the Management of IBS.

Irritable bowel syndrome (IBS) guidelines are generally developed by experts, with the possibility of a translational gap in clinical medicine. The aim of our study was to assess an Italian group of general practitioners (GPs) for their awareness and use of criteria for the diagnosis and management of IBS. For this purpose, a survey was carried out involving 235 GPs, divided into two groups according to their years of activity: 65 "junior general practitioners" (JGPs) (≤10 years) and 170 "senior general practitioners" (SGPs) (>10 years). JGPs were more familiar with the Rome IV Criteria and Bristol Scale than SGPs. Abdominal pain, bowel movement frequency and bloating were the symptoms most frequently used to make a diagnosis. The most probable causes of IBS were reported to be abnormal gastrointestinal motility and psychological triggers. SGPs reported more frequently than JGPs that challenging management and patient's request were motivations for a gastroenterological consultation. The practice of clinical medicine is still far from the guidelines provided by the specialists. Abdominal pain related to defecation and changes in bowel frequency are considered to be the more important symptoms for IBS diagnosis, but most GPs, both JGPs and SGPs, like to consider abdominal bloating as another useful symptom. Involving both gastroenterologists and GPs in developing shared guidelines would be highly desirable in order to improve IBS management strategies in everyday clinical practice.

Pharmacotherapeutic advances for chronic idiopathic constipation in adults.

INTRODUCTION: Chronic idiopathic constipation is a common gastrointestinal disorder whose treatment is still far from being satisfactory for patients. Osmotic laxatives, in particular polyethylene glycol, are the first-line approach, but new emerging pharmacological agents may be useful in refractory patients. AREAS COVERED: Published articles regarding the development and clinical efficacy of new agents in treating chronic idiopathic constipation were reviewed. Among emerging agents, elobixibat, a drug blocking the reabsorption of bile acids, is a promising one, especially in slow transit constipation. Linaclotide, lubiprostone and plecanatide, by a secretagogue action, improve stool consistency and increase colonic transit. Apart from prucalopride, approved in Europe for refractory chronic idiopathic constipation patients, the selective 5-HT4 agonists velusetrag and naronapride are in advanced development. In addition, relamorelin, a ghrelin agonist, seems promising for accelerating colonic transit. EXPERT OPINION: Several new promising drugs have been released with the potential to be effective in the treatment of chronic idiopathic constipation. On the other hand, the experience with these new agents is still limited, especially for long-term treatment. Another important point is that these new treatments for chronic idiopathic constipation are not available worldwide and their use could be somewhat limited by their still relatively high cost.