Cystic fibrosis is an autosomal recessive disorder seen worldwide, with typically a higher prevalence in Caucasians (11). A significant problem in developing countries is that CF patients have a shorter life expectancy, with many patients diagnosed at a later stage in life once symptoms of the disease have manifested (28). This study showed that the average age of diagnosis is after the age of nine, with only 38.3% of patients been diagnosed before five years of age. Later stage diagnosis is common among developing countries, while in high-income countries, more than 95% of the patients are diagnosed during the first year of life (11, 29).
In our sample of patients, respiratory symptoms (cough, recurrent pneumonia, dyspnea on exertion and chest pain) were more commonly described, followed by gastrointestinal symptoms including abdominal distention, increased frequency of stools, flatulence and steatorrhea. The clinical presentation in Ecuadorian patients appears to be similar to those reports from other Latin-American countries (23, 30). As often reported, BMI values are often low, and malnutrition has manifested. In our analysis, we found that the patients had an average BMI of 16.6 kg/m2, with girls showing greater average BMI values (17.4 kg/m2) compared to the boys (15.8 kg/m2). Culhane et al. reported higher BMI values for girls being slightly lower (21 kg/m2) than boys (22 kg/m2), probably due to increased energy losses, increased energy needs or differences in inadequate calorie intake among boys (31). Despite the later diagnosis of the disease, malnutrition was presented in only a quarter of our patients. The Shwachman-Kulczycki scores of ‘good’ or ‘excellent’ were seen in more than 70% of patients. This grading system is often used to track progress in these types of patients (32, 33).
In terms of comorbidities, a diagnosis of asthma in CF patients is difficult due overlapping respiratory symptoms. Nevertheless, around 20 to 30% of the patients with CF can have a concomitant clinical diagnosis of Asthma in population studies (34, 35). Our results show that 33% of our patients had this comorbidity, which is compatible with previous works.
The FEV1, FVC and the Tiffeneau-Pinelli index were within the normal range in the majority of patients. Mild lower airway obstruction was seen in all age groups, which is an interesting finding since lung function would have been expected to be lower in patients with a delayed CF diagnosis, as reported elsewhere (33). Lung function during follow-up at nine months post-diagnosis seems to be preserved. This maintenance seems to be paradoxical, findings probably related to the quality of management, process that includes correct antibiotic management and appropriate follow-up schemes (36).
Preventing complications is essential for this type of disease management; periodical cultures had proven to be an important clinical step to take when looking to prevent further complications and to implement early treatment when needed. In our report, the most common microorganism reported was Staphylococcus aureus, with varying antibiotic sensitivity profiles. The main differences are displayed in terms of age groups, showing a lower incidence of Moraxella catharralis and Haemophilus influenzae among cultures from patients over 10 years, while these patients have an increase in the number of positive cultures for S. aureus and Pseudomonas aeruginosa, an observation previously reported elsewhere (37). The presence of P. aeruginosa within the respiratory tract is often used as a positive marker for severity among children and adults with CF (38, 39). This type of infection accelerates lung-function deterioration and increases the cost of treatments (40, 41). In our results, P. aeruginosa was detected in 12.5% of airway cultures, and those patients were treated immediately with a double regimen of broad-spectrum intravenous (IV) antibiotics.
In terms of genetic findings, CFTR exhibits an important allelic heterogeneity, a situation in which different mutations in the same gene produce variations in clinical manifestations, with this heterogeneity well known to be related to different ethnic origin (27, 42–44). For example, the F508del mutation was the most commonly reported alteration among our patients. At least 52.7% of patients were carriers, with most being heterozygotes. Around the world, this mutation accounts for an estimated 30% to 80% of pathogenic variants, a percentage that usually varies across regions, countries and ethnic groups (45).
An important finding of our report is the presence of the H609R mutation (caused by the transition of adenosine to guanine at nucleotide 1958 - exon 13). To our best knowledge, this type of mutation has only been reported among Andeans offspring as probably damaging mutation (27,42–44). Among the thirteen patients (38.23%) with a complete sequence, only two patients displayed a homozygous state, while six had a compound heterozygous profile with the presence of the F508del mutation (27,44).
The other mutations had been previously described in Ecuadorian patients with CF (27,44). Nefzi et al. analyzed Latin American CF patients and found four common mutations: F508del (31.37%), G542X (1.96%), G85E (1.96%) and N1303K (1.96%), with 63.7% of Ecuadorian CF mutations remaining unidentified (42). In the second report, in order of frequency, the mutations reported were F508del (37.1%), G85E (8.9%), G542X (2.4%), N1303K (2.4%), with a detection rate of 53.22% of the total of CF patients studied. All four of these mutations were found in our tested patients in the following percentage: 52.77%, 5.56%, 11.11%, and 11.11%, respectively.
CFTR exhibits an important allelic heterogeneity, a situation in which different mutations in the same gene produce variations in clinical manifestations, with this heterogeneity well known to be related to ethnic origin, as we can exemplify with H609R mutation which has only reported in Hispanic offspring (27, 42–44). The other common mutations G542X, G85E and N1303K have been consistently found in Ecuadorian patients, with frequencies greater than that of Caucasian mutation panels.
In seven of our patients, the polymorphism c.204099A>C was reported, all in homozygous state, this polymorphism has been reported only in Ecuadorian populations (27), with most of these patients also showing known pathological mutations. This combination of polymorphisms plus mutations show a variety of phenotypes in patients, such as nutritional compound, microbiological cultures, respiratory spirometry values or as a combined effect. As Polizzi et al. describe there is a direct relation between phenotype with the specific mutation panel (46). Most severe cases with c.204099A>C polymorphism were between 10 to 15 years related to H609R and F508del/W1098X mutations, where in the first patient it was an important nutritional compound and in the second there were more complications and respiratory deterioration. In addition, related to Ecuadorian population, Moya et al. found in H609R homozygous patients a severe clinical CF (44), this contrast with our first patient that only have a heterozygous alteration with an important nutritional implication. In the second case, Sebro et al. describe F508del in the heterozygous compound, which there is a statistical association between this mutations and sweat chloride level, pancreatic function and Pseudomonas infection risk (47), this is compatible with complications of our patient. Finally, CFTR2 databases describe that patients with W1098X mutation have a predictive value in the range 62 - 100% (48), as it has been seen in our patient.
In four of our patients, the polymorphism c.206359C>A was reported in homozygous state. All of them were related to F508del/W1098X, G85E/H609R, and G970S mutations, however, the first case was described in combination with c.204099A>C polymorphism as opposed to c.206359C>A. In the second patient, there was no marked nutritional alteration, with sweat testing measures showing a low value, the respiratory function was partially conserved, and only one hospital admission was seen. Decaesteker et al. describe that patients with G85E had a significantly higher sweat chloride, higher prevalence of pancreatic insufficiency, worse current weight for height and higher prevalence of chronic P. aeruginosa colonization. However, these findings are not highly concordant with our patient (46). The last case demonstrates slight malnutrition, common bacteria colonization for the age and normal respiratory function. Therefore, there was phenotypic concordance, but there were no studies available about the clinical involvement of G970S mutation in the available literature.
During genetic analysis there was a unique case with polymorphisms c.204099A>C and c.206359C>A in combination with a benign polymorphism M470V. This patient showed only sweat test positive, but there was no malnutrition, microbiological alteration nor complications during the study period. However, sequential spirometry test results were unavailable due to the participant’s age. Moreover, M470V has been described as a benign polymorphism with slight respiratory problems and recurrence, and no positive sweat test (49). The unique presence of that polymorphism combination (c.204099A>C, c.206359C>A and 470V) in addition to the unexpected positive sweat test make this case a unique opportunity for further investigation and follow-up in order to find more information about its phenotype expression, its management and its prognosis.
Limitations:
This study was not exempt from limitations. Patients were sampled from one hospital in Ecuador; therefore, a complete extrapolation to the entire Ecuadorian population might be inaccurate. To have a better understanding of the clinical, genetic and microbiological features of CF in Ecuador, a larger sample size, over multiple hospitals around the country would be needed. Another limitation was the access to funding and equipment. Due to the lack of resources and finance, only 36 of the 47 patients underwent a genetic analysis, a selection that was allocated on a first-come, first-served basis, a decision made according to the presence of available funding. In addition, the lack of a quality asthma research center made it difficult for doctors to test for bronchial hypersensitivity according to international standards, tests that would have been valuable for this type of research.