A Systematic Review and Meta-Analysis of Stature Growth Complications in β-thalassemia Major Patients

Background: Blood transfusion is a traditional treatment for β-thalassemia (β-thal) that improves the patients’ anemia and lifespan, but it may lead to iron overload in parenchymal tissue organs and endocrine glands that cause their dysfunctions as the iron regulatory system can’t excrete excess iron from the bloodstream. Objective: To evaluate the prevalence of iron-related complications (short stature, growth retardation, and growth hormone deficiency) in β-thalassemia major (βTM) patients. Methods: We performed an electronic search in PubMed, Scopus, and Web of Sciences to evaluate the prevalence of growth hormone impairment in β-thalassemia major (βTM) patients worldwide. Qualities of eligible studies were assessed by the Joanna Briggs Institute checklist for the prevalence study. We used Comprehensive Meta-Analysis (Version 2) to calculate the event rate with 95% CIs, using a random-effects model for all analyses. Findings: Seventy–four studies were included from five continents between 1978 and 2019; 70.27% (Asia), 16.21% (Europe), 6.75% (Africa), 2.70% (America), 1.35% (Oceania), and 2.70% (Multicenter). The overall mean age of the participants was about 14 years. The pooled prevalence of short stature (ST) was 48.9% (95% CI 35.3–62.6) and in male was higher than female (61.9%, 95% CI 53.4–69.7 vs. 50.9%, CI 41.8–59.9). The pooled prevalence of growth retardation (GR) was 41.1% and in male was higher than in female (51.6%, 95% CI 17.8–84 vs. 33.1%, CI 9.4–70.2). The pooled prevalence of growth hormone deficiency (GHD) was 26.6% (95% CI 16–40.8). Conclusion: Our study revealed that near half of thalassemia patients suffer from growth impairments. However, regular evaluation of serum ferritin levels, close monitoring in a proper institute, suitable and acceptable treatment methods besides regular chelation therapy could significantly reduce the patients’ complications.


INTRODUCTION INFORMATION SOURCES AND SEARCH
We did an electronic search of PubMed, Scopus, and Web of Sciences to December 31, 2019, without language restrictions. Search term combinations were "B-thalassemia transfusiondependent," "Beta-Thalassemia major," "endocrine complication," "iron-related complication," "short stature," "growth hormone," and "growth retardation." All reference lists from the included studies and relevant systematic reviews were hand-searched for additional studies (see Appendix 1 for full search strategy in PubMed database).

STUDY SELECTION
After the search was completed, all records were imported to EndNote V.8, and then duplicate records were removed. The titles, abstracts, and full-text records were screened based on the pre-mentioned inclusion and exclusion criteria. All records are screened by two independents reviewers. A third reviewer reviewed the record in case of discrepancy, and disagreement was resolved by consultation.

DATA COLLECTION PROCESS AND DATA ITEMS
Two independent reviewers extracted and tabulated all relevant data using a researcher-made checklist. The disagreement was resolved by consensus between all authors. The data extraction checklist includes items like author name, published year, country of origin, study design, source of data gathering, sample size, gender information, the mean age of participants, and prevalence data regarding complication. A third reviewer rechecked the extracted data.

QUALITY APPRAISAL
All the studies were checked in term of quality by two independent reviewers using a 9-items Joanna Briggs Institute checklist for a cross-sectional study [14]. The potential disagreement was resolved by consultation with a third reviewer. This checklist includes nine-question and four rating scores (Yes, No, Unclear, and Not applicable). Each question was scored 1 point for yes, 0 points for unclear and no. Then, studies were categorized as having a high risk of bias if the summary score was 0 to <4, moderate risk of bias if the summary score was between 4 to <7 points, and low risk of bias if the summary score was between 7 to 9 points [15,16].

STATISTICAL ANALYSIS
Publication bias was assessed by visual inspection of funnel plots Egger's test and Begg's test. The standard error of prevalence was calculated from the reported percentage prevalence and sample size for each study. We used Comprehensive Meta-Analysis (Version 2) to calculate the event rate with 95% CIs, using a random-effects model for all analyses. If data is available, we also performed subgroup analyses based on region and gender to decrease heterogeneity. I 2 was also measured to assess heterogeneity between the included studies [17]. Although there was heterogeneity between the studies, this was negligible due to differences in context as well as the use of different source of data. However, a subgroup analysis based on regions and a meta-regression based on mean age of the participant were conducted to increase the reliability of the results.

STUDY SELECTION
The total search yielded 1024 records. After the removal of duplicates, 646 records were screened based on title and abstract. After that, 433 records were excluded, and 213 records entered fulltext assessment for eligibility criteria. Finally, 74 studies included in the meta-analysis (Figure 1) [6,7,11,.

QUALITY APPRAISAL
The JBI tool for quality assessment of included studies yielded scores ranging from 2 to 9. The mean methodological quality was 6.9 out of 9. Fifty-six studies were classified as low risk of bias (75.67%), seventeen were a moderate risk of bias (22.97%), and one study was of a high risk of bias (1.35%). Details of the answers to the tool's nine questions are given in Appendix 2.
We did not suspect any evidence of publication bias (Begg's test P = .711 and Egger's test P = .602). The visual inspection of the funnel plot did not show significant publication bias (Appendix 3).

SYNTHESIS OF RESULTS
The meta-analyses' results on the prevalence of the different types of investigated complications in βTM patients are shown in Table 2.

SHORT STATURE
Forty-six studies encompassing 3832 participants reported the prevalence of ST. The pooled prevalence of ST was 48.9% (95% CI 35.3-62.6). Based on subgroup analyses by world region,   the pooled prevalence of ST varied between regions, but these differences were not significant (Figure 2). Based on world region subgroup analyses, the pooled prevalence for males was higher than females (61.9%, 95% CI 53.4-69.7 vs. 50.9%, CI 41.8-59.9) (Figure 3).   Table 2 The pooled prevalence of endocrine complications in β-thalassemia transfusiondependent patient.

GROWTH RETARDATION
Eighteen studies encompassing 4418 participants reported the prevalence of GR. The pooled prevalence of GR was 41.1% (95% CI 27.5-56.4). Based on world region subgroup analyses, the pooled prevalence of GR varied between regions, but these differences were not significant (Figure 4). Based on world region subgroup analyses, the pooled prevalence for males was higher than females (51.6%, 95% CI 17.

GROWTH HORMONE DEFICIENCY
Thirteen studies encompassing 4101 participants reported the prevalence of GHD. The pooled prevalence of GHD was 26.6% (95% CI 16-40.8). Based on subgroup analyses by world region, the pooled prevalence of GHD varied between regions, but these differences were not significant (Figure 6). Not enough information was available for subgroup analysis by gender in this variable.

DISCUSSION
As there is no permanent cure for TM patients, blood transfusion is still the best solution for reducing these problems. There are no unique means in the human body for eliminating the overload of iron, which consequent from a blood transfusion. There is 200 to 250 mg iron in every unit of the packed cell. The amounts of daily iron which is accumulated in different organs of TM patients is approximately 0.3 to 0.6 mg/kg [89]. Introducing iron-chelating therapy besides using noninvasive techniques same as T2 MRI, has been improved different functional complications in βTM patients [90]. However, there is no consensus on treating endocrine disorders resulting from iron overload thoroughly [89]. Also, a systematic review reported that only 54 % of βTM patients utilize chelation therapy regularly. So, this kind of treatment is not well-accepted by the people [91]. Overload of iron leads to severe heart failure complications, hepatic disorders, endocrine dysfunction, skeletal deformities, and growth impairment. The secondary effect of that on the growth hormone-insulin-like growth factor axis leads to ST, GR, and GHD due to deposition of iron in the pituitary gland [91,92].
This study is the first systematic review and meta-analysis about growth impairments in βTM patients in the world. The prevalence rate of ST, GR, and GHD was 48.9%, 41.1%, 26.6%, respectively. Several studies proved that ST is one of the most common endocrine disorders in βTM patients as we did [1,11,30,76].
Short stature is a multifactorial complication. However, one of the causes is the shortening of patients' trunks disproportionately due to delayed-chelating therapy and hypogonadism [93]. The pituitary gonadotropes are incredibly vulnerable to oxidative stress caused by iron deposition in the hypothalamus and pituitary gland [9]. De Sanctis et al. evaluated the prevalence rate of ST among 3023 βTM patients in 16 countries and reported that 53% were short. These authors also reported that by comparing endocrinopathies of βTM with intermediate β-thal, endocrine disorders like ST in βTM patients are overloaded by iron [3].
We found that 41.1% of βTM patients all around the world are growth retarded. Some explanations containing hyper-metabolism, chronic anemia, hypoxia (especially in under-treated children), defects in secretion of gonadotropin, deposition of iron in thyroid, gonads, pituitary and adrenal glands, diabetes, liver disease, zinc and folic acid deficiency, emotional factors, nutritional deficiencies, and deferoxamine-induced bone dysplasia are suggested [1,51,94,95]. Oxidative stress with iron overload can make the anterior part of the pituitary dysfunctional. Furthermore, Growth Hormone-Insulin-Like Growth Factor-1 (GH-IGF1) axis disorders result in growth deceleration [96].
Our understandings of GHD in βTM patients were confirmed by many studies like Yassin, Gulati, and Hamidiah et al [8,37,41]. They all have accordance with our results. Yassin suggests that the higher deposition of iron in the liver, the higher prevalence of complications like GHD [8]. Also, an increase in the somatostatinergic tone on GH release justifies impaired GH secretion [9]. GHD is also affected by increasing hypothyroidism and delayed puberty. With the longer life span of these patients, the probability of GHD increases [55].
Based on our analyses, the pooled prevalence of ST and GR for males was higher than females. The probable reason is females can endure iron toxicity better than males due to chronic oxidative stress [97,98].
Taher et al., have claimed that geographical differences affect an iron overload in βTM patients [89]. One of the main reasons is that βTM patients can have different genetic predispositions to the toxicity of iron deposited in the endocrine gland and serum ferritin. Also, the amount of iron overload in a patient depends on how much the patient is under observation, follow-up, and treatment, how often they are under chelation therapy, and when the first desferrioxamine therapy was started [84]. But our findings indicate no significant differences in ST, GR, and GHD deficiencies of βTM patients among various populations.
In addition to our results, several studies had different ideas about the noticeable effect of serum ferritin levels on growth impairments. Hashemi et al. reported in a survey containing seventy transfusion-dependent thalassemic as that in patients with ST, the mean serum ferritin level was considerably more than patients of standard height [99]. This point is also defined by other studies like Hamidah et al. conducting an issue on 26 pre-pubertal βTM or HbE-β thal who were transfusiondependent (serum ferritin was higher in patients under the third percentile of height [4,567.0 vs. 2,271.0, P = 0.01]) and Shalitin et al. who somehow got the same result while acknowledging that if the patients do not begin chelation therapy before puberty with high quality, they appear shorter in height [77,100].
Nevertheless, Grundy and coworkers are the opponents of this idea, reporting no relationships between the SD scores and the well or poorly chelated patients. They suggested genetic factors, racial and socioeconomic means, and urbanism as the most probable reasons for ST [36]. Some factors like; age (the older the patient gets, the more prevalent the ST is), hemoglobin level, age of the first chelation therapy, and genotype impacts on prevalence of endocrine dysfunction in βTM patients [11,87,101,102]. βthal patients start transfusing blood at an earlier age; therefore, this genotype is related to iron overload and more endocrine complications. The growth impairments generally happen in patients with β°β° genotype more severe than those with β°β+ and β+β+ [103]. Therefore, clinical complications of the diseases are directly related to the genotype of βTM patients.

CONCLUSION
Many βTM patients are suffering from GR, ST, and GHD all around the world. Among, the prevalence of ST was more common, especially in patients older than seven years old. By noticing the control of patients' serum ferritin levels, GH can be diagnosable. With close monitoring in a proper institute, suitable and acceptable treatment methods besides regular chelation therapy and follow-up, the patients can significantly reduce their complications.

RECOMMENDATION FOR FUTURE RESEARCH
The results of our study show that the number of studies conducted to investigate these complications is low in some countries where βTM is common. Therefore, further studies in this field are recommended. Using high transfusion and modern chelation in low and middle-income countries can generally prevent the disease from occurring, so, the cooperation of international organizations, especially the WHO, seems to be essential for setting up a central laboratory for low-and middle-income countries. It is necessary to investigate the reasons for families avoiding diagnostic tests, and training and educational courses should be developed following these reasons. It is difficult to counter the misconceptions that prevent such tests, but it requires roundthe-clock efforts, and the support of health care professionals is crucial, and the development of such supportive strategies requires further study.

ADDITIONAL FILES
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ETHICS AND CONSENT
This article uses the secondary data of published studies and does not contain studies with human participants or animals.