Pseudo-vitamin D deficiency: absence of 25-hydroxyvitamin D 1 alpha-hydroxylase activity in human placenta decidual cells

Pseudo-Vitamin D Deficiency Rickets (PDDR), an heritable defect in renal 25-hydroxyvitamin D 1 alpha-hydroxylase activity, leads to insufficient synthesis of 1 alpha, 25-dihydroxyvitamin D (calcitriol) and the early onset of severe rickets which can only be offset by replacement therapy with calcitriol. The nature of the underlying mutation remains unknown. Hydroxylation of 25-hydroxyvitamin D in the 1 alpha-position is not restricted to the renal tubular cells. We have previously shown that human decidual cells do produce calcitriol and that the enzyme activity was regulated by feedback mechanisms. We now demonstrate that cells isolated from the decidua of PDDR patients lack that function making them likely targets for the mutation. This suggests that the decidual and renal enzymes (or a controller of their activity) are encoded by the same gene. Thus the PDDR placenta represents a source of mutant cells for further investigation of the PDDR molecular defect.

Congenital primary cutaneous osteoma: biochemical and histological studies

Biopsies of a cutaneous osteoma and of normal-looking skin from a 1-year-old girl were studied for histological appearance and collagen biochemistry. The mineralized tissue contained a matrix similar to bone: Only type I collagen, with a hydroxylysine content (0.48%) higher than in the skin (0.35%) and dihydroxylysinonorleucine as the major reducible crosslink. As expected, the normal skin adjacent to the lesions contained type I and type III collagen and as major crosslinks hydroxylysinonorleucine and histidinohydroxymerodesmosine. Histological studies showed the presence of woven bone with very little trabeculation. Numerous active osteoblasts were laying down a rapidly calcified non-lamellar matrix. Osteocytes and multinucleated osteoclasts were also noted. The study demonstrates the osseous nature of the lesion and suggests that an abnormal cell differentiation is associated with this form of osteoma.

Accuracy of measurements of small changes in soft-tissue mass by dual-energy x-ray absorptiometry

OBJECTIVE

To assess the ability of dual-energy x-ray absorptiometry (DXA) to measure accurately small changes in lean soft-tissue mass. DXA has recently been suggested as an accurate, noninvasive method of analysis of body composition.

DESIGN

Experimental use of DXA to assess human body composition before and after rapid saline infusion.

PARTICIPANTS

Six healthy men.

OUTCOME MEASURES

Weight measurements, DXA scanning results and skinfold thicknesses taken on the first day of the experiment and on the second day, before and after rapid saline infusion.

RESULTS

After the infusion, the subjects' weight increased by a mean 2.26 kg (standard deviation 0.199 kg). At each of the four readings, there was a strong correlation between weight and DXA-derived total mass (r = 0.999) and between skinfold-derived fat-free mass and DXA-derived lean mass (r = 0.941 to 0.957). Following infusion, no differences were found between the measured and theoretical (i.e., preinfusion value plus weight change) values for total mass (p = 22), lean soft-tissue mass (p = 0.10) and lean mass (p = 0.09). The bias was -0.669 (95% confidence interval [CI] 0.18 to -1.49) for total mass, -0.65 (95% CI 0.16 to -1.47) for lean soft-tissue mass, and -0.14 (95% CI 0.11 to -0.38) for lean mass.

CONCLUSIONS

DXA is an improvement over- previous dual-energy technologies and appears to provide sufficient accuracy to detect small (less than 2.5 kg) changes in mass in individual, healthy men, over a short period and under non-steady-state conditions. Therefore, DXA may also be of practical use for longitudinal assessment of weight change.

Principles and results of corrective lower limb osteotomies for patients with vitamin D-resistant hypophosphatemic rickets

Forty-four lower limb osteotomies were performed in ten patients with vitamin D-resistant hypophosphatemic rickets. The average follow-up period was 51 months. Osteotomies were combined with shortening and compression plating. This allowed corrections of angular deformities in the sagittal plane as large as 70 degrees and in the coronal plane as large as 78 degrees. There was one complication, a compartment syndrome that resolved completely following prompt fasciotomy. Recurrence of deformity occurred in 27% of the cases. While osteotomies were safe and provided dramatic improvement to limb deformity, postoperative control of vitamin D metabolism was the one constant factor for maintenance of correction.

Osteogenesis imperfecta at the beginning of bone and joint decade

Osteogenesis imperfecta (OI), or brittle bone disease, is a heritable disorder characterized by increased bone fragility. Four different types of the disease are commonly distinguished, ranging from a mild condition (type I) to a lethal one (type II). Types III and IV are the severe forms surviving the neonatal period. In most cases, there is a reduction in the production of normal type I collagen or the synthesis of abnormal collagen as a result of mutations in the type I collagen genes. These classic forms of OI are described in this review. There are instances, however, where alterations in bone matrix components, other than type I collagen, are the basic abnormalities of the OI. Recently, three such discrete types have been identified by histomorphometric evaluation (types V and VI) and linkage analysis (Rhizomelic OI). They provide evidence for the as yet poorly understood complexity of the phenotype-genotype correlation in OI. We also discuss bisphosphonates treatment as well as fracture management and surgical correction of deformities observed in the patients with OI. However, ultimately, strengthening bone in OI will involve steps to correct the underlying genetic mutations that are responsible for this disorder. Thus, we also describe different genetic therapeutic approaches that have been tested either on OI cells or on available OI murine models.

Cortical bone material / compositional properties in growing children and young adults aged 1.5-23 years, as a function of gender, age, metabolic activity, and growth spurt

Bone material / compositional properties are significant determinants of bone quality, thus strength. Raman spectroscopic analysis provides information on the quantity and quality of all three bone tissue components (mineral, organic matrix, and tissue water). The overwhelming majority of the published reports on the subject concern adults. We have previously reported on these properties in growing children and young adults, in the cancellous compartment. The purpose of the present study was to create normative reference data of bone material / compositional properties for children and young adults, in the cortical compartment. We performed Raman (Senterra (Bruker Optik GmbH), 50× objective, with an excitation of 785 nm (100 mW) and a lateral resolution of ~0.6 μm) microspectroscopic analysis of transiliac bone samples from 54 individuals between 1.5 and 23 years of age, with no known metabolic bone disease, and which have been previously used to establish histomorphometric, bone mineralization density distribution, and cancellous bone quality reference values. The bone quality indices that were determined were: mineral/matrix ratio (MM) from the integrated areas of the v₂PO₄ (410-460 cm^-1) and the amide III (1215-1300 cm^-1) bands, tissue water in nanopores approximated by the ratio of the integrated spectral area ~ 494-509 cm^-1 to Amide III band, the glycosaminoglycan (GAG) content (ratio of integrated area 1365-1390 cm^-1 to the Amide III band, the sulfated proteoglycan (sPG) content as the ratio of the integrated peaks ~1062 cm^-1 and 1365-1390 cm^-1, the pyridinoline (Pyd) content estimated from the ratio of the absorbance height at 1660 cm^-1 / area of the amide I (1620-1700 cm^-1) band, and the mineral maturity / crystallinity (MMC) estimated from the inverse of the full width at half height of the v₁PO₄ (930-980 cm^-1) band. Analyses were performed at the three distinct cortical surfaces (endosteal, osteonal, periosteal) at specific anatomical microlocations, namely the osteoid, and the three precisely known tissue ages based on the presence of fluorescence double labels. Measurements were also taken in interstitial bone, a much older tissue that has undergone extensive secondary mineralization. Overall, significant dependencies of the measured parameters on tissue age were observed, while at any given tissue age, sex and subject age were minimal confounders. The established Raman database in the cortical compartments complements the previously published one in cancellous bone, and provides healthy baseline bone quality indices that may serve as a valuable tool to identify alterations due to pediatric disease.

Analysis of the type of collagen present in osteoarthritic human cartilage

Abnormal synthesis of type I collagen by fibrocartilage has been suggested as a mechanism involved in degenerative arthritis. Samples of normal and osteoarthritic adult femoral head cartilage were thus studied for histology and collagen composition. The electrophoretic analysis of the cyanogen bromide-derived peptides showed the sole presence of type II collagen in all normal and in all osteoarthritic samples, except those in which fibrocartilage was present. The sensitivity of the technique would not permit, however, the detection of a minute amount (less than 3%) of type I collagen in the samples. The results show that massive deposition of type I collagen occurs only when fibrocartilage is formed. It is suggested that this fibrocartilage is formed when the subchondral bone is damaged.

Mapping autosomal recessive vitamin D dependency type I to chromosome 12q14 by linkage analysis

Linkage analysis in French-Canadian families with vitamin D dependency type I (VDD1) demonstrated that the gene responsible for the disease is linked to polymorphic RFLP markers in the 12q14 region. We studied 76 subjects in 14 sibships which included 17 affected individuals and 17 obligate heterozygotes. Significant results for linkage were obtained with the D12S17 locus at the male recombination fraction (theta m) .018 (Z[theta m theta f] = 3.20) and with D126 at (theta m = .025 (Z[theta m theta f] = 3.07). Multipoint linkage analysis and studies of haplotypes and recombinants strongly suggest the localization of the VDD1 locus between the collagen type II alpha 1 (COL2A1) locus and clustered loci D12S14, D12S17, and D12S6, which segregate as a three-marker haplotype. Linkage disequilibrium between VDD1 and this three-marker haplotype supports the notion of a founder effect in the studied population. The current status of the localization of the disease allows for carrier detection in the families at risk.

[Purpura fulminans]

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The use of bisphosphonates in children with osteogenesis imperfecta

Children with osteogenesis imperfecta (OI) suffer recurrent fractures resulting in pain, deformity and disability. There is no accepted medical therapy for the condition other than symptomatic pain relief, and surgical correction of the deformities. Recent experience with the bisphosphonate group of drugs suggests, however, that anti-resorptive therapy may reduce fracture frequency, increase bone density, promote remodeling of previously crush-fractured vertebrae, reduce chronic pain, and improve mobility in both children and infants. The prospects for preventing disability and deformity, and perhaps improving growth in affected children are good. Current studies are focusing on the evaluation of the efficacy of oral drug therapy, and protocols are under development to evaluate new, more efficient molecules. Until gene therapy becomes a reality, the use of bisphosphonates appears to be the most efficient way of altering the natural course of severe OI, and improving the quality of life of patients.

Early diagnosis in Niemann-Pick disease

Hepatosplenomegaly, observed on routine physical examination of a 3-month-old French-Canadian infant, was the first evidence for the possibility of Niemann-Pick disease. Vacuolated foam cells filled with phospholipid material were found in liver and bone marrow biopsy material. The absence of sphingomyelinase activity in isolated peripheral leukocytes and cultured skin fibroblasts confirmed the diagnosis. The parents' leukocytes displayed significantly less activity than was found in control cells. Exact and early confirmation of the diagnosis of Niemann-Pick disease is of prime importance for it allows the physician to offer a more specific prognosis, to provide more precise genetic counselling for the couple at risk and, finally, to offer the possibility of prenatal diagnosis.

Bisphosphonate therapy for severe osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heterogeneous group of disorders principally affecting type I collagen. Children with the severe forms of the condition suffer recurrent fractures resulting in limb and spine deformities, and restricted ambulation. Recently, cyclical intravenous administration of pamidronate has proven of benefit to children with the severe forms of OI. Bone mineral density increased, and the incidence of fractures decreased. The treatment does not alter fracture healing, growth rate, or growth plate appearances. Dependence on mobility aids is reduced and there is substantial relief of chronic pain and fatigue. No significant adverse side effects have been noted. New bisphosphonates are under investigation to compare their effects to those of pamidronate. Although the use of bisphosphonates does not address the basic abnormalities that underlie the OI syndromes, it represents the first therapy to significantly alter the natural course of the disease and improve patients' clinical status and quality of life.

Effects of hyperprolactinemia on calciotropic hormones

Serum 1,25-dihydroxyvitamin D, parathyroid hormone, calcium, phosphorus and alkaline phosphatase levels as well as the renal handling of phosphorus were measured in female patients with hyperprolactinemia. Despite elevated prolactin levels, none of the patients showed an imbalance of the biochemical parameters of mineral homeostasis. Neither surgery nor bromocriptine treatment, both of which brought PRL within the normal limits, had an appreciable effect on the circulating concentrations of mineral and calciotropic hormones. These results do not allow us to assign a definite role to PRL in the control of mineral metabolism in man.

Simultaneous measurement of serum 25-hydroxycholecalciferol and 25-hydroxyergocalciferol

A method for the selective measurement of serum 25-hydroxycholecalciferol and 25-hydroxyergocalciferol has been developed. The two hydroxysecosteroids were measured in a control group and in a group of ambulatory patients treated chronically with anticonvulsant drugs. In both groups the serum levels of 25-hydroxycholecalciferol and 25-hydroxyergocalciferol followed a log normal distribution. No significant difference could be elicited between the control and the treated groups for either hydroxysecosteroid. Furthermore the data shows how important is the dietary source of vitamin D in our environment.

Molecular cloning of (25-OH D)-1 alpha-hydroxylase: an approach to the understanding of vitamin D pseudo-deficiency

Pseudovitamin D-deficiency rickets (PDDR) is the first identified inborn error of vitamin D metabolism. Its clinical course is similar to that of nutritional rickets due to simple vitamin D deficiency. The treatment of choice is replacement therapy with calcitriol [1,25(OH)2D3]. PDDR is inherited as a simple autosomal recessive trait. The PDDR locus has been mapped to chromosome 12q13-q14. The molecular defect underlying the 25-hydroxyvitamin D-1 alpha-hydroxylase enzyme dysfunction has remained elusive due to the lack of sequence information for the gene encoding the cytochrome P450 moiety of the enzyme. We have used a probe derived from the rat 25-hydroxyvitamin D-24-hydroxylase sequence to identify and clone the 1 alpha-OHase cDNA. The candidate gene was transiently expressed in P19 embryonal carcinoma cells. Only those cells that were transfected with the candidate cDNA in the sense orientation were able to produce a compound that co-eluted with the 1 alpha, 25 vitamin D3 standard. Mass spectrometry analysis confirmed the identity of the produced metabolite. A human genomic clone was isolated from a chromosome 12 cosmid library and subsequently mapped to human chromosome 12q13.1-q13.3. To address the putative biological function of 24,25-dihydroxyvitamin I) 24,25(OH)2D, we also engineered a null mutation in the 24-OHase gene in embryonic stem cells (ES). Animals heterozygous for the engineered mutation are normal and fertile. One half of the homozygous animals die before weaning. Breeding of surviving females gives an F2 generation in which bone development is abnormal at sites of intramembranous ossification. Growthplate maturation and endochondral ossification appeared to proceed normally. The results show that a complete absence of vitamin D metabolites hydroxylated in position 24 during embryogenesis leads to abnormal bone structure and suggests a key role for 24,25(OH)2D in the developmental regulation of intramembranous ossification.

Linkage disequilibrium analysis in young populations: pseudo-vitamin D-deficiency rickets and the founder effect in French Canadians

Pseudo-vitamin D-deficiency rickets (PDDR) was mapped close to D12S90 and between proximal D12S312 and distal (D12S305, D12S104) microsatellites that were subsequently found on a single YAC clone. Analysis of a complex haplotype in linkage disequilibrium (LD) with the disease discriminated among distinct founder effects in French Canadian populations in Acadia and in Charlevoix-Saguenay-Lac-Saint-Jean (Ch-SLSJ), as well as an earlier one in precolonial Europe. A simple demographic model suggested the historical age of the founder effect in Ch-SLSJ to be approximately 12 generations. The corresponding LD data are consistent with this figure when they are analyzed within the framework of Luria-Delbrück model, which takes into account the population growth. Population sampling due to a limited number of first settlers and the rapid demographic expansion appear to have played a major role in the founding of PDDR in Ch-SLSJ and, presumably, other genetic disorders endemic to French Canada. Similarly, the founder effect in Ashkenazim, coinciding with their early settlement in medieval Poland and subsequent expansion eastward, could explain the origin of frequent genetic diseases in this population.