Abstract. Familial dysautonomia (FD) patients suffer from multiple fractures and have reduced bone pain, which defers the diagnosis. The pathogenesis of bone.
Osteoporos Int (2002) 13:429–433 ß 2002 International Osteoporosis Foundation and National Osteoporosis Foundation
Osteoporosis International
Original Article Bone Mineral Density and Metabolism in Familial Dysautonomia C. Maayan1, E. Bar-On2, A. J. Foldes3, B. Gesundheit1 and R. Dresner Pollak4 Departments of 1Pediatrics, 4Internal Medicine and the 3Jerusalem Osteoporosis Center, Hadassah University Hospital, Mount Scopus, Hebrew University Hadassah Medical School, Jerusalem, and 2Pediatric Orthopedic Unit, Schneider Children’s Medical Center of Israel, Rabin Medical Center Petach-Tikva, Israel
Abstract. Familial dysautonomia (FD) patients suffer from multiple fractures and have reduced bone pain, which defers the diagnosis. The pathogenesis of bone fragility in FD is unknown. This study aimed to characterize bone mineral metabolism and density in FD. Seventy-nine FD patients aged 8 months to 48 years (mean age 13.9 10.4 years, median 12.3) were studied. Clinical data included weight, height, bone age, weekly physical activity and history of fractures. Bone mineral density (BMD) of the lumbar spine (n = 43), femoral neck (n = 26), total hip (n = 22) and whole body (n = 15) were determined by dual-energy X-ray absorptiometry. Serum 25-hydroxyvitamin D3, osteocalcin, bone alkaline phosphatase (B-ALP), parathyroid hormone and urinary N-telopeptide cross-linked type 1 collagen (NTx) were determined in 68 patients and age- and sex-matched controls. Forty-two of 79 patients (53%) sustained 75 fractures. Twenty-four of 43 patients had a spine Z-score 5–2.0, and 13 of 26 had a femoral neck Z-score 5–2.0. Mean femoral neck BMD Z-score was lower in patients with fractures compared with those without (–2.5 0.9 vs –1.5 1.0, p = 0.01). Mean body mass index (BMI) was 16 kg/m2 in prepubertal patients and 18.4 kg/m2 in postpubertal patients. Bone age was significantly lower than chronological age (75.5 vs 99.3 months in prepubertal patients, p50.001; 151 vs 174 in postpubertal patients, p50.05). NTx and osteocalcin levels were higher in FD patients compared with controls (400 338 vs 303 308, BCE/mM creatinine p50.02; 90 59.5 vs 61.8 36.9 ng/ml, p50.001, respectively). BALP was lower in FD patients compared with controls Correspondence and offprint requests to: Channa Maayan, MD, Department of Pediatrics, Hadassah University Hospital, Mount Scopus, PO Box 24035, Jerusalem 91240, Israel. Tel: +972 2 5844510. Fax: +972 2 6510804.
(44.66 21.8 vs 55.36 36.6 ng/ml, p50.04). Mean spine Z-score was significantly lower in physically inactive compared with active patients (–3.00 1.70 vs –1.77 1.3, respectively, p = 0.05). We conclude that fractures in FD patients are associated with reduced BMD. FD patients have increased NTx and osteocalcin. Contributing factors include reduced BMI, failure to thrive and reduced physical activity. Preventive therapy and early diagnosis are essential. Keywords: Bone mineral density; Bone turnover markers; Familial dysautonomia; Fractures; Osteopenia; Osteoporosis
Introduction Familial dysautonomia (FD) is an autosomal recessive disease affecting the autonomic, sensory and motor nervous systems. The disease occurs essentially among Ashkenazi Jews, in whom the incidence is 1:3703 [1]. The FD gene was recently mapped to chromosome 9q31 [2]. The pathogenesis of the disease is unknown. Neuropathologic findings include a decrease in mainly unmyelinated neuronal fibers as well as paucity of neurons in the spinal cord and in sensory and autonomic ganglia [3]. The clinical manifestations result from severe autonomic and sensory dysfunction involving most of the organ systems. There is discoordination of the gastrointestinal tract with misdirection of food and fluids into the lungs, gastroesophageal reflux and vomiting crises resulting in recurrent aspirations and chronic lung disease. These patients suffer from labile blood pressure with postural hypotension and dizziness affecting their gait and stability. The main neurologic
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deficits include: lack of overflow tears, impaired pain sensation including bone pain, decreased corneal reflex, decreased or diminished deep-tendon reflexes, developmental delay, convulsions, and lack of axon flare after intradermal injection of histamine [4]. FD patients suffer from various skeletal disorders including severe kyphoscoliosis, foot deformities, arthropathies and multiple fractures [5]. We have previously reported the incidence of fractures to be 40% of FD patients with a mean of 1.5 fractures per patient [5]. Since these patients have reduced bone pain, their fractures are diagnosed at a late stage, thereby complicating the treatment. The mechanisms of multiple fractures in FD have not been elucidated. The aim of the present study was to characterize bone mineral metabolism and density in FD patients. To our knowledge this is the first study on this subject in FD. The results may increase our understanding of recurrent fractures in FD and possibly in other diseases with sensory autonomic neuropathies.
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Osteoporosis Center, Jerusalem, using a Hologic QDR 4500 apparatus. The coefficients of variation of our BMD measurements are 1.2% for the total hip, 1.8% for the femoral neck and 1.2% for the lumbar spine. In the adult patients (above 18 years of age) BMD was measured at the lumbar spine (anteroposterior projection) and the proximal femur (femoral neck and ‘total’ hip regions). In patients under 18 years of age BMD was measured at the lumbar spine and, in some of them, also at the proximal femur and/or whole body (see Table 3). The results of patients’ BMD measurements were compared with control values matched for age and gender, and were expressed as units of standard deviations of the mean control value (Z-score). The adoption of the Z-score compensated for any inherent inconsistency derived from the employment of various DXA models in the study. Control values were derived from normal databases provided by the manufacturers. In the case of children and adolescents studied by Hologic machines, control values for femoral and whole body BMD were derived from the published literature [7,8].
Subjects and Methods The study was carried out on 79 FD patients, consisting of 42 males and 37 females. All patients had been followed at the Familial Dysautonomia Center, Hadassah University Hospital, Mount Scopus, Jerusalem, Israel, since 1982. The diagnosis of FD was confirmed by FD signs and symptoms [4], a positive histamine test [4] and by genetic markers [6]. Patients’ ages ranged from 8 months to 48 years (mean 13.9 10.4, median 12.3 years). The following clinical data were obtained: age, weight, height, 50% weight and height ages (the age at which the patient’s height and weight would equal the 50th percentile), use of medications known to affect bone mineral metabolism, bone age, past history of fractures and amount of weight-bearing activity. The estimated weight-bearing physical activity was graded according to the number of hours of walking per week; grade 1, 8–10 h/week; grade 2, 4–7 h/week, grade 3, below 4 h/week. Body mass index (BMI) was calculated (kg/m2). The Ethics Committee of Hadassah University Hospital approved the study protocol. Informed consent was obtained from patients or their guardians.
Bone Mineral Density Bone mineral density (BMD) was measured by dualenergy X-ray absorptiometry (DXA). The measurements were performed at various diagnostic centers using either a Hologic apparatus (models QDR 4500 and QDR 1000, Hologic, Waltham, MA) or Lunar apparatus (models DPX and DPX-IQ, Lunar, Madison, WI). A third of BMD measurements were performed at the Hadassah
Biochemical and Endocrine Measurements Serum measurements included total calcium, phosphorus, total protein, albumin and thyroid stimulating hormone (TSH). Arterial pH was also determined. 25hydroxyvitamin D3 (25(OH)vitD3) was measured by RIA (IncStar, Stillwater, MN). Serum intact parathyroid hormone (PTH) was measured by N-tact PTH SP IRMA kit (DiaSorin, Stillwater, MN). Serum estradiol level was previously measured in the female patients included in this study [9]. Biochemical markers of bone turnover were studied in 68 FD patients and in healthy gender- and age-matched controls. The serum tests for bone formation included osteocalcin and bone-specific alkaline phosphatase (BALP). Serum total osteocalcin (OC) was measured with a human-specific two-site immunoradiometric assay (IRMA; ELSA-OSTEO, Cis Biointernational, Bagnols, Ceze, France). The intra- and interassay coefficients of variation (CVs) were below 4% and 6%, respectively, and sensitivity was 0.4 ng/ml. Serum B-ALP (ng/ml) was measured with a human-specific IRMA (Ostease, Hybritech, San Diego, CA). The sensitivity of the assay was 0.2% and the intra- and interassay CVs were 7% and 9% respectively. Urinary N-telopeptide cross-linked collagen type I (NTx), a marker of bone resorption, was measured in a second morning void (Osteomark, Ostex International, Seattle, WA). The intra- and interassay coefficients of variation were less than 8%, and sensitivity was 25 nmol/l. The measurements were corrected by the urinary creatinine concentration measured by a standard calorimetric method, and are expressed as bone collagen equivalent (nmol BCE/mmol creatinine).
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Data Analysis
Table 2. Distribution of fractures and age of occurrence
Descriptive statistics are presented as mean standard deviation of the mean (SD), unless otherwise specified. The values of B-ALP, osteocalcin and NTx in FD patients and controls were compared using a Wilcoxon signed rank test. Data were analyzed for prepubertal and postpubertal patients as well as for the whole group. Bone age was compared with chronological age using a paired t-test. FD patients with fractures were compared with those without fractures by non-paired t-test. Comparisons between the three groups of patients divided by degree of physical activity were performed with two-way ANOVA. p50.05 was defined as statistically significant. All analyses were performed using Statistix software package (Analytical Software, Tallahassee, FL).
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Results Clinical Characteristics The clinical characteristics of the study population are presented in Table 1. There were 57 (33 male, 24 female) prepubertal and 22 (9 male, 13 female) postpubertal patients. The mean age at puberty was 15.5 2.2 years in females and 17.8 2.1 years in males. Twenty percent of patients were treated with Maalox (Rhoˆne-Poulenc Rorer) and/or Gaviscon (R & C). Thirty percent of the patients were treated with anticonvulsants but none was on idantoin, and only one patient was on chronic glucocorticoid therapy for bronchial asthma. FD patients were small and short for their age. The mean age compatible with their height and weight at the 50th percentile was only 8 years. Mean BMI in prepubertal patients was 16 kg/m2 and in postpubertal patients was 18.4 kg/m2 (p = 0.001). Mean BMI in prepubertal patients corresponded to the 10th percentile for height and weight at their mean age of 13.9 years. Mean bone age determined in 25 patients was 76 months compared with 99 months of chronological age (paired t-test, p50.001) in 20 prepubertal patients, and 151 months compared with 174 months in 5 postpubertal patients (paired t-test, p50.05). There were no gender differences with respect to mean chronological age, BMI, or mean age compatible with height and weight at 50th percentile. Mean BMI was Table 1. Clinical data of 79 FD patients Male/female Age (years) Weight (kg) Height (m) BMI (kg/m2) % patients with one fracture % patients with two fractures % patients with three or more fractures Weight-bearing physical activity (walking h/week) Data are mean SD.
42/37 13.9 28.0 1.26 16.6 26.6 13.9 12.5 8.9
10.4 13.3 0.27 2.6
5.0
Radius and/or ulna Tibia and/or fibula Humerus Calcaneus and/or metatarsus Femur Metacarpal and/or fingers Clavicle Patella Mandible
No. of fractures
23 16 13 7 7 5 2 1 1
Age (years) Mean SD
Median
8.4 10.8 5.3 6.6 17.1 6.2 8.5 22 10
9 8.4 5 3 18 7
4.7 9.8 2.6 5.7 9.7 3.2
significantly lower in prepubertal patients (16 2.2 kg/ m2 vs 18.42.7 kg/m2, p50.01). Forty-two of 79 patients (53%) had a total of 75 fractures (Table 1). The distribution of fractures is presented in Table 2. Over 50% of fractures (39/75) occurred at the radius, ulna, tibia and fibula. Fractures occurred mostly in the upper limbs before puberty and in the lower limbs after puberty (Table 2). The mean age of occurrence of all fractures was 9.1 7.1 years with a median age of 8 years. There was no difference in mean fracture number with respect to gender or pubertal stage. There were no significant differences in mean BMI between pre- and postpubertal FD patients who sustained a fracture and those who did not. Twenty-eight patients were physically active at grade 1, 36 patients at grade 2 and 15 patients at grade 3. There were no statistically significant differences between these three groups with respect to gender, mean age, pubertal stage, BMI and number of fractures.
Bone Mineral Density Lumbar spine BMD measurements with appropriate Zscores were obtained in 43 randomly selected patients (30 prepubertal, mean age 7.9 4 years; 13 postpubertal, mean age 29.6 10.6 years). Z-scores for the femoral neck, total hip and whole body BMD measurements were available for 26 (14 prepubertal, mean age 9.43.2 years; and 12 postpubertal, mean age 30.1 10.9 years), 22 (13 prepubertal, mean age 9.4 3.4 years; 9 postpubertal, mean age 30.1 9.9 years) and 15 prepubertal patients, respectively. Mean Z-scores for the lumbar spine, femoral neck, total hip and whole body are presented in Table 3. In the first three sites more than 90% of patients studied had a negative Z-score, implying a BMD value that is below the expected value of healthy subjects matched for age and gender. Furthermore, at least 50% of the patients studied had a Z-score 5–2.0, indicating a marked reduction in BMD, equivalent to the 3rd percentile or less of the age- and gender-matched expected value. Mean whole body Z-score was reduced to a lesser extent, with 33% of the patients having a Z-score 5–2.0. There
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Table 3. BMD Z-Scores at the various measured sites n
Lumbar spine 43 Femoral neck 26 Total proximal femur 22 Whole body 15
Z-score (mean SD)
Patients with Z-score 50 (%)
Patients with Z-score 4–2.0 (%)
–2.0 –2.1 –2.2 –1.2
91 96 100 80
53 54 50 33
1.43 1.05 1.06 1.3
were no gender differences in mean BMD Z-scores of the lumbar spine, total hip, femoral neck and total body. Pre-pubertal patients had a significantly lower spinal Z-score compared with postpubertal patients (–2.4 1.2 vs –1.2 1.6, p = 0.008). No such difference was found at the femoral neck or total hip. Mean femoral neck BMD Z-score was significantly lower in patients with fractures compared with those without (–2.5 0.9 vs 71.5 1.0, p = 0.01). There were no significant differences in spine, total hip, and whole body BMD Zscores between these two groups. Mean spine Z-score was significantly lower in physically inactive patients (grade 3) compared with relatively active patients (grade 1) (–3.0 1.8 vs –1.8 1.3, respectively, p = 0.05).
Biochemical Measurements Mean serum levels of calcium, phosphorus, TSH, 25(OH)vitD3, PTH, total protein, albumin and arterial pH in FD patients were within normal limits (Table 4). Nine percent of the patients had vitamin D deficiency defined as 25(OH)vitD3 510 ng/ml. Mean serum levels of B-ALP, osteocalcin and urinary NTx in FD patients and controls are presented in Table 4. Serum osteocalcin and urinary NTx levels were significantly higher in FD patients compared with ageand sex-matched controls. On the other hand, B-ALP Table 4. Indices of bone mineral metabolism in FD patients and in age- and sex-matched controls
Osteocalcin (ng/ml) B-ALP (ng/ml) NTx (nmol BCE/mmol Cr) Total protein (g/l) Albumin (g/l) Ca (mM/l) P (mM/l) PTH (pmol/l) 25(OH)vitD3 (ng/ml) Arterial pH
n
FD patients
68 68 68 67 66 68 68 54 56 68
90 44.7 400 73.2 40.6 2.4 1.4 5.1 25.4 7.4
Normal range
59.5** – 21.9* – 338* – 7.4 60–80 4.2 35–50 0.1 2.0–2.6 0.3 0.8–1.4 5.6 1.2–6.8 13 10–45 0.03 7.35–7.45
Controls
61.8 36.9 55.4 36.6 303 308 – – – – – – –
Data are mean SD. *p50.05 FD patients versus controls; **p50.01 FD patients versus controls.
levels were significantly lower in FD patients compared with age- and gender-matched controls. Serum osteocalcin was significantly higher in prepubertal FD patients who had sustained fractures compared with those without a previous fracture (112 50 vs 84 32 ng/ml, p = 0.01). There were no significant differences between patients with fractures and those without in mean 25(OH)vitD3, PTH, B-ALP and NTx. There were no gender differences in all biochemical measurements except for serum osteocalcin level which was significantly lower in females compared with males (71.5 35.6 ng/ml vs 99.2 33.8 ng/ml, p = 0.02 in females and males respectively).
Discussion The unselected FD group of patients studied had a high prevalence of fractures (450%) and significantly reduced BMD. Markers of bone formation and resorption, osteocalcin and urinary NTx, were higher in FD patients compared with age- and sex-matched controls. Since FD patients have a higher threshold of bone pain, the diagnosis of a fracture in these patients may be delayed for months. Furthermore, osteoporosis may play a role in the pathogenesis of their spinal deformities, and has been shown to impair the fixation of spinal fusion operations often performed in these patients [5]. Several factors can contribute to decreased BMD and increased fracture incidence in FD. These patients consume decreased amounts of dairy products due to recurrent aspirations and the possible deleterious effect of dairy products, which can aggravate bronchial hypersensitivity and increase the risk of aspiration. Phosphorus absorption might be impaired in these patients by chronic antacid therapy, such as aluminum hydroxide, as it combines to form insoluble compounds of aluminum phosphate. Most FD patients consume antacids regularly for the management of their gastroesophageal reflux. Even patients who have undergone fundoplication and gastrostomy operations consume antacids during FD crises or acute illness. Interestingly, vitamin D deficiency was uncommon in our patients, possibly due to high exposure to sun in Israel. FD patients in our study had a significantly low BMI, a known risk factor for decreased BMD. Low BMI in FD patients is probably a marker of their chronic illness, and results from decreased caloric intake and frequent dysautonomic crises characterized by, among other symptoms, nausea and vomiting [4]. Other indicators of failure to thrive and chronic illness in our patients include reduced bone age compared with their chronological age and the discrepancy between their mean chronological age and the calculated mean age compatible with their height and weight at the 50th percentile. FD patients were shorter for their age. It is noteworthy that the short stature of our patients may induce a downward skew in their BMD readings. While protein malnutrition was previously reported as a major risk factor for osteoporosis in the pediatric age group
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[10], there was no evidence of protein malnutrition in our patients, suggested by their normal serum albumin level. Weight-bearing physical activity plays a major role in bone acquisition and the maintenance of bone mass. Impaired mobility, hypotonia and decreased weightbearing are believed to account for increased osteoporosis risk in central nervous system and neuromuscular diseases [11]. The mean estimated number of hours of walking per week in our FD patients was only 8.9 5. Furthermore, FD patients in our study who were the least active had the lowest spine BMD Z-scores compared with the more active group. Moreover, FD patients suffer from ataxia, gait instability and are prone to recurrent falls, further increasing their fracture risk. Thus, fracture risk in FD patients increases not only due to decreased bone strength but also due to their increased propensity for falling. Skeletal mineralization is affected by normal sexual maturation in both females and males. We have previously shown that menarch in FD females is delayed (average age 15.5 years) compared with their unaffected mothers (average age 13.6 years), although the sex hormone profile was normal [9]. Delayed puberty with a lower estrogen exposure score was previously shown to be associated with decreased bone mass in adolescent girls [12]. We speculate that extreme blood pressure fluctuations, a typical symptom in FD patients, might affect bone perfusion and may also contribute to their bone disease. Bone disease due to vascular changes was previously described in FD [5,13]. Significant alterations of blood pressure can affect bone perfusion, and may account for the clinical presentations of Legg-Calve-Perthes disease in two of our patients and navicular bone necrosis in another one. These patients had no other apparent cause for their vascular bone disease. Thus, the role of bone perfusion in the pathogenesis of bone fragility in FD needs to be studied further. We have previously demonstrated reduced plasma calcitonin gene-related peptide (CGRP) in FD [13]. CGRP is a prominent neurotransmitter in C-fibers, which are involved in thermo-, mechano- and nociception perception, and FD patients were found to have reduced C-fibers [3]. CGRP was shown to inhibit osteoclastic bone resorption in vitro [14]. Furthermore, CGRP was also found to have effects on osteoblasts, increasing mineral formation [15]. We hypothesize that decreased local CGRP levels in FD can explain their lack of bone pain and adversely affect bone turnover. In this study increased levels of osteocalcin and NTx were found in FD patients compared with age- and sexmatched controls. B-ALP was lower in FD patients compared with controls. Since patients and controls were not matched for their pubertal stage, their higher bone markers could be partially explained by delayed puberty. In addition, low body weight accompanied by a low muscular mass can result in a low urinary creatinine, and
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thus artificially increased values of urinary creatininecorrected NTx [16]. In addition, the limitations of the clinical utility of bone markers in the pediatric age group should be taken into account. We conclude that FD patients are among the pediatric groups at risk for osteopenia and osteoporosis. Since the time of diagnosis can be delayed due to lack of bone pain, there should be awareness of falls and limb swelling because of a possible fracture. Our findings in FD patients may have clinical and therapeutic implications. Calcium, vitamin D supplement and a high-calorie diet should be provided. Elevated bone markers suggested increased bone turnover. Thus, antiresorptive agents, such as the bisphosphonates, may be effective in fracture prevention in these patients.
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