Mutations in the gene encoding the RER protein FKBP65 cause autosomal-recessive osteogenesis imperfecta.

Osteogenesis imperfecta is a clinically and genetically heterogeneous brittle bone disorder that results from defects in the synthesis, structure, or posttranslational modification of type I procollagen. Dominant forms of OI result from mutations in COL1A1 or COL1A2, which encode the chains of the type I procollagen heterotrimer. The mildest form of OI typically results from diminished synthesis of structurally normal type I procollagen, whereas moderately severe to lethal forms of OI usually result from structural defects in one of the type I procollagen chains. Recessively inherited OI, usually phenotypically severe, has recently been shown to result from defects in the prolyl-3-hydroxylase complex that lead to the absence of a single 3-hydroxyproline at residue 986 of the alpha1(I) triple helical domain. We studied a cohort of five consanguineous Turkish families, originating from the Black Sea region of Turkey, with moderately severe recessively inherited OI and identified a novel locus for OI on chromosome 17. In these families, and in a Mexican-American family, homozygosity for mutations in FKBP10, which encodes FKBP65, a chaperone that participates in type I procollagen folding, was identified. Further, we determined that FKBP10 mutations affect type I procollagen secretion. These findings identify a previously unrecognized mechanism in the pathogenesis of OI.

Effective parenteral clodronate treatment of a child with severe juvenile idiopathic osteoporosis.

UNLABELLED: We report on an 8 years and 3 months old boy with severe idiopathic juvenile osteoporosis (IJO). Clinical features included multiple fractures, especially of the vertebrae, and neurological symptoms. Biological studies showed non-parathyroid hormone-mediated excessive bone resorption and massive urinary calcium loss. Although IJO is usually a self-limiting condition after puberty, the severity of our patient's manifestations required therapeutic intervention. Clodronate (dichloromethylene-bisphosphonate) was administered parenterally every 3 months for a period of 2 years. Dramatic clinical and biochemical improvement was noted within 2 weeks. All parameters of bone resorption normalised and no new fractures occurred. After 6 months of treatment, radiological improvement with healing of fractures and rebuilding of the vertebral plates was documented. Bone mineral density increased to normal within 1 year and growth velocity was accelerated. After 2 years, treatment was stopped at the age of 10 years and 3 months. One year later, back pain and increasing pain in the knee region recurred. A tibial fracture was evident and, again, bone mineral density was far below normal. Bisphosphonate medication was reinstituted leading to rapid improvement. No side-effects were observed. CONCLUSION: Parenteral clodronate therapy is effective in managing severe idiopathic juvenile osteoporosis.

Wolcott-Rallison Syndrome: clinical, genetic, and functional study of EIF2AK3 mutations and suggestion of genetic heterogeneity.

Wolcott-Rallison syndrome (WRS) is a rare autosomal-recessive disorder characterized by the association of permanent neonatal or early-infancy insulin-dependent diabetes, multiple epiphyseal dysplasia and growth retardation, and other variable multisystemic clinical manifestations. Based on genetic studies of two inbred families, we previously identified the gene responsible for this disorder as EIF2AK3, the pancreatic eukaryotic initiation factor 2alpha (eIF2alpha) kinase. Here, we have studied 12 families with WRS, totalling 18 cases. With the exception of one case, all patients carried EIF2AK3 mutations resulting in truncated or missense versions of the protein. Exclusion of EIF2AK3 mutations in the one patient case was confirmed by both linkage and sequence data. The activities of missense versions of EIF2AK3 were characterized in vivo and in vitro and found to have a complete lack of activity in four mutant proteins and residual kinase activity in one. Remarkably, the onset of diabetes was relatively late (30 months) in the patient expressing the partially defective EIF2AK3 mutant and in the patient with no EIF2AK3 involvement (18 months) compared with other patients (<6 months). The patient with no EIF2AK3 involvement did not have any of the other variable clinical manifestations associated with WRS, which supports the idea that the genetic heterogeneity between this variant form of WRS and EIF2AK3 WRS correlates with some clinical heterogeneity.