Introduction

The α-thalassemias are the most common inherited disorders of hemoglobin synthesis. It caused by mutations in one or more of the four α-globin genes, leading to decreased or absent α-globin chain production [1].

Hemoglobin H (HbH) disease is caused by deletion or dysfunction of three of four α-globin alleles. The people with α-thalassemia intermedia or HbH disease usually have moderate anemia. This causes a phenotype of mild to moderate chronic hemolytic anemia. Hemoglobin H patients may require intermittent transfusion therapy especially during hemolytic or aplastic crises. Hemoglobin H disease is characterized by the presence of hepatosplenomegaly, microcytic hypochromic anemia, intraerythrocytic inclusion bodies. Other complications include infections, leg ulcers, gall stones, folic acid deficiency, and sometimes mild to moderate thalassemia-like bone changes that mainly affect the facial features [2–6].

Osteoporosis is a skeletal disease characterized by a generalized reduction in bone mineral density (BMD), microarchitectural deterioration of bone tissue, leading to increased bone fragility and significantly higher frequency of fractures [7–9].

Osteopenia and osteoporosis are important causes of morbidity in adult patients of both genders with β-thalassemia major (TM) or intermedia (TI). Osteoporosis is a multifactorial disease, thought to be mediated by an interaction between environmental factors as well as genetic factors. It is accepted that multiple acquired factors including liver disease, aging, genetic disorders of osteogenesis, endocrine disorders, and delay in sexual maturation are involved in the pathogenesis of osteoporosis in thalassemia [10–12].

Several studies have shown reduced bone mass and high rates of fracture in patients with TM and TI [13–15]. Based on our knowledge, data regarding bone density in HbH disease is limited; on the other hand, α-thalassemia and HbH disease is not rare in our population [16].

Our aim was to investigate the status of BMD and possibly related factors in patients with HbH disease.

Material and methods

In this cross sectional study, we evaluated BMD and bone mineral content (BMC) in 21 patients over age 10 out of 37 Iranian patients with HbH disease, from November 2014 to August 2015, who were followed at an outpatient Thalassemia Clinic in Shiraz, Southern Iran. Also, we selected a sex- and age-matched control group (n = 21) for comparison of BMD and BMC.

Exclusion criteria were other forms of thalassemia intermedia syndrome including β-thalassemia intermedia, sickle thalassemia, and HbE-thalassemia. Inclusion criterion was HbH disease in patients over 10 years old.

An informed written consent form was filled by those who accepted to take part in the study. The study was approved by the Ethics Committee of Shiraz University of Medical Sciences.

Diagnosis of HbH disease was based on complete blood cell (CBC), Hb electrophoresis and peripheral smear by checking inclusion bodies and gene analysis in some of them. The results of alpha globin gene analysis in patient number 1 showed --Med and −α3.7 (−−Med/-α3.7) and in patient number 12 showed α-5 nt α/--Med (double heterozygous α + and α0).

All patients were non-transfusion dependent and took folic acid 5 mg/kg orally once a day.

We measured fasting serum calcium (Ca) and phosphate (P) with enzymatic colorimetric method by Hitachi 911 (Japan). 25-Hydroxy vitamin D (25OH-D) was measured with enzyme-linked immunosorbent assay (ELISA) method with DLD diagnostika kit (Germany) in all included patients. Fasting serum ferritin was measured with enzyme-linked fluorescent assay (ELFA) technology by mini Vidas analyzer (Biomerieux, France).

According to the International Society for Clinical Densitometry (ISCD) Official Position definition, a Z-score of −2.0 or lower was defined as “below the expected range for age,” and a Z-score above −2.0 was regarded as “within the expected range for age” [17]. At the time of the study, no patient received any treatment such as bisphosphonate, following our results we referred our patients to endocrinologist if they needed treatment by bisphosphonate.

Lumbar spines (L1–L4) and right femur neck BMD and BMC were measured by means of dual energy X-ray absorptiometry (DXA) method by Lunar DPX-IQ densitometer, and the results were expressed as Z-score which are units of standard deviation (SD). Z-score is defined as the number of SDs above or below the mean for age- and sex-matched subjects. The BMD and BMC results were, respectively, expressed as mean values (g/cm2) ± SD and (g) ± SD.

Statistical analysis

Data analysis was done by SPSS software version 17 (SPSS Inc, Chicago IL, USA). Comparison of quantitative variables between the two groups was done by Mann-Whitney test. Qualitative variables were compared by Chi-square test between the two groups. P value less than 0.05 was considered statistically significant.

Results

The demographic and paraclinical data of the patients are illustrated in Table 1.

Table 1 Demographic, clinical, and paraclinical characteristics of the study population with hemoglobin H disease
Full size table

Mean age of the patients was 20.23 ± 9.87 years and ranged from 11–56 years old.

Prevalence of patients with BMD in the lumbar spine below the expected range for age was 33.3 %. Also, 14.3 % of our patients suffered from BMD with below the expected range for age in the femur neck region.

We compared different variables including BMI, Ca, P, ferritin, Hb, HbF, T4, TSH, and 25OH-D levels in patients with BMD below the expected range for age. There was no significant association in any of the evaluated variables with BMD in the lumbar and femur neck (P value >0.05). A total of five (13.5 %) patients were splenectomized. The hypothyroidism was seen only in one patient with normal Z-score of BMD within the expected range for age.

Bone mineral density showed no significant association with age, sex and splenectomy (P value >0.05).

Table 2 shows comparison of BMD and BMC values between the patient and control groups. Lumbar BMD was significantly lower in the patients compared to controls (median (min-max) 0.725 (0.595–0.924) vs. 1.061 (0.645–1.238), P < 0.001)).

Table 2 Bone mineral density and bone mineral content values of patients with hemoglobin H and controls
Full size table

Discussion

Our study shows a prevalence of 33.3 % of patients with BMD in the lumbar spine below the expected range for age. In addition, 14.3 % of our patients suffered from BMD with below the expected range for age in the femur neck region. Moreover, value of lumbar BMD was significantly lower in our patients in comparison with healthy individuals.

Some studies showed that fractures occurred more frequently among patients with TM and TI compared to the other thalassemia syndromes [18]. In one study, Jeans et al. showed osteoporosis or osteopenia in 96 % of patients with TM [19]. It seems that osteoporosis prevalence in HbH disease is less in comparison with other thalassemia intermediate syndromes. However, further studies with larger groups of patients are recommended.

In our study, no association was found between any of the evaluated variables with BMD in the lumbar and femur neck.

Several studies have shown reduced bone mass in osteoporotic patients with thalassemia [20–22]. Additional studies found that osteopenia and osteoporosis are emerging as important causes of morbidity in patients of both genders with thalassemia [14, 19, 23–25].

Taher et al. evaluated 548 patients with β-TI showed osteoporosis as the most common disease-related complication (22.9 %) [26]. In HbH disease, ineffective erythropoiesis is less common than β-TI. It seems that osteopenia and osteoporosis in HbH is less common than in β-TI which was confirmed in our study.

In conclusion, based on our results, it seems to be rational to evaluate BMD in patients with HbH after age of ten and treat them if necessary despite its frequency is less than in TM and TI beta thalassemia patients.