Diagnosis of hypochondroplasia: the role of radiological interpretation. Italian Study Group for Hypochondroplasia.

BACKGROUND: Hypochondroplasia is characterised by phenotypic and genetic heterogeneity. Differentiation from other conditions with disproportionate short stature is often difficult. OBJECTIVE: To determine the reliability of radiological interpretation in the diagnosis of hypochondroplasia and to evaluate the most typical skeletal abnormalities. These data were correlated with molecular findings. MATERIALS AND METHODS: We enrolled 21 patients with suspected hypochondroplasia based on the radiological criteria most often reported in the literature on this disease. Height, sitting height and head circumference were measured in all patients. Radiographs of the lumbar spine, left leg, pelvis and left hand were obtained. The presence of the N540K mutation in the fibroblast growth factor receptor 3 (FGFR3) gene was verified by restriction enzyme digestion. All radiographs which enabled the selection of patients were reviewed a second time by two paediatric radiologists in a blinded examination. Their results were compared. RESULTS: Both radiologists confirmed the diagnosis in 10 out of 21 patients, while in the other 52% of cases they excluded the disease, were uncertain or they did not agree on the final interpretation of the data. The best agreement rate was obtained in the evaluation of the lumbar spine and the legs. The radiological features of the nine patients (43%) carrying the N540K substitution were not remarkably different from the ones reported in the patients without this mutation. CONCLUSION: Our study shows that the crucial skeletal regions on which to focus the diagnosis of hypochondroplasia are the lumbar spine and legs, while the pelvis and hands seem to be less characteristic. To reduce the risk of misdiagnosis, accurate radiological and clinical evaluation is needed, especially in cases without a defined genetic defect.

Urinary markers of bone turnover in healthy children and adolescents: age-related changes and effect of puberty.

During growth, bones change their dimensions rapidly with the changes involving both formation and resorption processes. Small cross-linked peptides coming from type I collagen molecules are excreted in urine when bone is resorbed. To date, conflicting results have been presented concerning the age- and puberty-related changes of urinary markers. The purpose of the present study was to verify the effect of age, gender, and puberty on the urinary excretion of type I collagen degradation products in healthy children and adolescents. Timed spot urines from 176 children (4-20 years old) and 50 young adults were analyzed. The concentrations of N-telopeptides of type I collagen (NTx), pyridinolines (Pyr), and deoxypyridinolines (Dpyr) were measured, and the results were normalized to creatinine. Age-related changes in cross-links excretion were observed. The levels decreased with age, and a peak of excretion was shown at the beginning of adolescence. Prepubertal levels of all the markers were four- to five-fold higher than in adults, and they decreased towards adult levels in late puberty. Girls had significantly higher levels of all biochemical markers than boys at pubertal stage 2. We also observed a remarkable effect of puberty on the levels of bone degradation products that was independent of age and gender. Our results indicate that bone resorption is high in children relative to that in adults, and that urinary levels of NTx, Pyr, and Dpyr change as a function of age, gender, and puberty.

Comparison of clinical-radiological and molecular findings in hypochondroplasia.

Hypochondroplasia is an autosomal dominant skeletal dysplasia characterized by disproportionate short stature. A mutation (N540K) in the fibroblast growth factor receptor 3 (FGFR3) gene was described in some patients with this condition. The aims of the study were to identify the frequency of the FGFR3 gene mutation, to define the salient clinical and radiological abnormalities of the affected subjects, and to verify the contribution of molecular findings to the clinical and radiological definition of hypochondroplasia. Based on the most common radiological criteria, we selected 18 patients with a phenotype compatible with hypochondroplasia. Height, sitting height, and cranial circumference were measured in all patients. Radiographs of the lumbar spine, left leg, pelvis, and left hand were also obtained. The presence of the N540K mutation was verified by restriction enzyme digestions. Half of our patients carried the N540K mutation. Although similar in phenotype to the patients without the mutation, they showed in addition relative macrocephaly. The association of the unchanged/narrow interpedicular distance with the fibula longer than the tibia was more common in patients with gene mutation. Although we did not find a firm correlation between genotype and phenotype, in our study the N540K mutation was most often associated with disproportionate short stature, macrocephaly, and with radiological findings of unchanged/narrow interpedicular distance and fibula longer than tibia.

Bone turnover in neonates: changes of urinary excretion rate of collagen type I cross-linked peptides during the first days of life and influence of gestational age.

New markers have been used to monitor the changes of bone turnover occurring during growth. Data on bone turnover rate during the perinatal period are, however, very scarce. In the present study we evaluated bone turnover rate, assessed by the measurement of urinary N-terminal telopeptide of type I collagen (NTx) concentrations, at different gestational ages, and we documented the trend of bone turnover rate occurring in the first days after birth. Urine samples were obtained from 83 healthy full term newborn infants, 16 preterm, and 17 infants of diabetic mothers (IDMs). The first miction after birth was collected. Urine samples were also collected 24 and 48 h after birth. NTx was measured by an enzyme-linked immunosorbent assay (Osteomark, Ostex International, Inc. Seattle, WA). The relationship between NTx at birth and all the other variables has been evaluated using multiple regression analysis. The changes of NTx excretion over time and the effect of the groups were studied by multivariate analysis of variance (MANOVA) for repeated measures. We found a remarkable association between gestational age and NTx concentrations at birth (R = 0.56; p < 0.00001). NTx concentrations showed a progressive decrement, reaching a nadir between the 38th and the 42nd week of gestation. The NTx concentrations changed significantly during the first 48 h of life in the three groups. Moreover, preterm infants had NTx excretion values at birth significantly higher than full term infants (p < 0.001), whereas NTx excretion rates of IDMs were not different from those of the other two groups of subjects. In conclusion, gestational age seems to be the major determinant of bone turnover in neonates; NTx excretion rate is higher before term, it slows in proximity of delivery, and it increases significantly during the first 48 h of life. Preterm infants have higher bone turnover rate than full term infants. NTx excretion rate of IDMs was comparable with those of the control subjects.

Bone modeling indexes at onset and during the first year of follow-Up in insulin-dependent diabetic children.

Osteopenia has been described as a complication of insulin-dependent diabetes mellitus (IDDM). We measured bone modeling indexes during the first year of IDDM. At each time point the values obtained from diabetic children have been compared with those of control subjects. We selected 27 prepubertal children with IDDM (6.35 +/- 2.16 years). We also enrolled 30 healthy prepubertal children of comparable age (5.85 +/- 3.05 years). Height, height standard deviation scores, glycated haemoglobin (HbA1C), basal c-peptide concentrations, insulin dose, serum concentrations of procollagen type I C-terminal propeptide (PICP), and collagen type I C-terminal telopeptide (ICTP) were measured at onset of IDDM and at 3, 6 and 12 months. ICTP was in the normal range at onset of IDDM and decreased during the follow-up to reach a significant difference compared to controls after 3, 6 and 12 months of insulin treatment (P < 0.04). PICP concentrations increased significantly at 3 months (P = 0.05) compared to onset. At 3 and 12 months PICP values were significantly higher than those of control children (P = 0.04). Correlations were found between PICP concentrations and HbA1C and c-peptide at onset of diabetes (r = -0.45 and r = 0.47, respectively). Bone formation at onset of IDDM is not impaired; the introduction of insulin therapy, together with the achievement of a good metabolic control, determines an increase of bone matrix formation coupled with a decrease of bone resorption, that determines a positive balance of bone modeling.

Bone density in young patients with congenital adrenal hyperplasia.

One of the major complications of glucocorticoid treatment is bone loss. 21-Hydroxylase deficiency is the most frequent inborn error of steroidogenesis, leading to congenital adrenal hyperplasia (CAH): synthesis of cortisol is impaired and replacement therapy is therefore mandatory. We studied the bone mineral density in a group of patients with congenital adrenal hyperplasia (CAH) on long-term glucocorticoid replacement therapy. We selected 30 Caucasian patients with CAH due to 21-hydroxylase deficiency (mean +/- SD age = 17.45 +/- 2.49 years). 22 patients had the classical CAH form and the remaining 8 had the nonclassical (late-onset) form. The mean duration of therapy was 15.20 +/- 4.04 years. Bone mineral density (BMD) was evaluated with a dual-energy X-ray absorptiometer. BMD was also measured in 73 healthy white volunteers of comparable age (17.35 +/- 2.99 years). BMD values of the spine (sBMD), total body (TBBMD), legs, and arms of CAH patients, adjusted for confounding variables (age, gender, body mass index), did not differ from those of control subjects (p = 0.86; p = 0.17; p = 0.06 and p = 0.26, respectively). sBMD and TBBMD values did not show relationships with the duration of treatment and the dose of corticosteroids. Patients with the classical form of CAH had bone density values comparable with those of patients with the nonclassical form (sBMD: p = 0.33; TBBMD: p = 0.97). Our data show that, despite long-term treatment with glucocorticoids, CAH patients have bone density values comparable with controls.

Human growth hormone treatment in prepubertal children with achondroplasia.

We studied the effects of recombinant human growth hormone (GH) treatment in 6 prepubertal children with achondroplasia. The patients' age ranged from 2 11/12 to 8 5/12 years and the GH dose was of 0.1 IU/kg/day subcutaneously. Auxological assessments and bone age determinations were performed 6 months before, at the beginning, and after 6 and 12 months of therapy. The growth velocity increase during the whole year of treatment ranged from 1.1 to 2.6 cm/year in 3 patients while in the others no variation was detected. No side effects were observed during the trial apart from a slight advancement of bone age in two patients. MRI at the cervicomedullary junction and CT scan of the base of the skull did not show any variation of the dimensions of the foramen magnum at the end of the trial compared to baseline. Our study shows that r-hGH can safely increase short-term growth velocity in some but not all prepubertal children with achondroplasia. Our data confirm the individual variability in the response to the GH treatment.

Bone mineral metabolism and thyroid replacement therapy in congenital hypothyroid infants and young children.

Impairment of calcium metabolism and low bone density have been found in hypothyroid adults. We investigated the effect of thyroid replacement therapy on calcium metabolism and bone mineralization in congenital hypothyroid (CH) infants and children. One hundred and 16 Caucasian CH consecutive patients were studied and were grouped according to their age: 23 patients at diagnosis, 20 at 3 mo, 24 at 6 mo, 25 at 12 mo and 24 at 36 mo. Thyroid replacement therapy was started at an initial dose of 6-8 micrograms/kg/day of L-thyroxine, and then decreased progressively. Calcium, phosphorus, magnesium, alkaline phosphatase (AP), parathyroid hormone (PTH) and osteocalcin (BGP) were measured as calcium metabolism indices. Bone mineral content (BMC) was measured at the mid-portion of the right radius AP, PTH and BGP concentrations were significantly higher in subjects at 3 mo of age (p < 0.05). This rise coincided with the end of the period of maximum dosage of L-thyroxine. Mild asymptomatic hypercalcemia was observed in 20 patients. All the other indices did not differ between age groups. BMC values and BMC annual increment were not different from those calculated for age-matched controls. We found that L-thyroxine replacement therapy does not alter bone mineralization of CH infants and children. Only a transitory increase of osteoblastic function was observed after the first few months of therapy.

Human 25-hydroxyvitamin D 24-hydroxylase cytochrome P450 subunit maps to a different chromosomal location than that of pseudovitamin D-deficient rickets.

We have cloned part of the human 25-OHD 24-hydroxylase cytochrome P450 (P450cc24) cDNA. The characterized sequence consists of 776 bp of the coding and 720 bp of the 3'-untranslated region interrupted by an intron. In the coding region we found 79.8% similarity in DNA and 87.5% in deduced amino acid sequences between human and rat, with no similarity in the 3'-untranslated region. By Southern blot hybridization of DNA from human-hamster somatic cell hybrids and by in situ immunofluorescence hybridization, we mapped P450cc24 to human chromosome 20q13.1. This location of P450cc24 is different from that of pseudovitamin D-deficient rickets (PDDR), previously assigned to chromosome 12q14 by linkage analysis, thus excluding it as a target of the PDDR mutation. Since it is likely that PDDR is caused by a mutation in the 25-OHD 1 alpha-hydroxylase P450 subunit (P450cc1 alpha) our results do not support the hypothesis that the two cytochromes are encoded by a single gene.

Effect of gluten-free diet on bone mineral content in growing patients with celiac disease.

Osteoporosis is a complication of celiac disease in adulthood, but little is known about the influence of the disease on bone mineralization in children. In the present study we evaluated radial bone mineral content (BMC) in celiac children and adolescents at diagnosis and after they consumed a gluten-free diet (GFD). The BMC values of 33 celiac patients at diagnosis were significantly lower than those of 255 control subjects (P < 0.001). There was no difference between diabetic and non-diabetic celiac patients. In 14 patients the BMC increased significantly (P < 0.05, ANCOVA) after 1.28 y of GFD. In these patients the mean annual BMC increment was 0.07 g/cm, significantly greater (P < 0.05) than the increment of normal growing children (0.05 g.cm-1.y-1). Our data indicate that although osteoporosis complicates celiac disease during childhood and adolescence, GFD alone is able to remarkably improve bone mineralization.