A case of neuroendocrine oncogenic osteomalacia associated with a PHEX and fibroblast growth factor-23 expressing sinusidal malignant schwannoma.

Oncogenic osteomalacia is a rare paraneoplastic syndrome that is characterized biochemically by hypophosphatemia and low plasma 1,25-dihydroxyvitamin D3, and clinically by osteomalacia, pseudofractures, bone pain, fatigue, and muscle weakness. We present a patient with a malignant schwannoma as the underlying cause of this disorder. A permanent cell line (HMS-97) derived from this tumor showed evidence of neuroendocrine differentiation by immunohistochemistry and of neurosecretory activity by electron microscopy. The cell line did express PHEX (phosphate-regulating gene with homologies to endopeptidases located on the X-chromosome) and FGF-23 (fibroblast growth factor-23) transcripts on northern hybridization; however, none of the known mutations from the related mendelian disorders of X-linked hypophosphatemic rickets or autosomal-dominant hypophosphatemic rickets could be detected. Tumor cell (HMS-97)-derived conditioned medium did not inhibit phosphate transport in a standard opossum kidney cell assay and in animal experiments. The medium also showed no PTH1- or PTH2-receptor-stimulating bioactivity. HMS-97 cells might be useful for further studies that aim to determine the genetic mechanism that leads to the observed PHEX and FGF-23 expression, both of which might have a direct role in the pathogenesis of oncogenic osteomalacia. In addition, these cells might be a useful tool for the investigation of neuroendocrine Schwann cell function and autoimmune peripheral nerve disease.

Characterization of marker chromosomes in Namalva cells by chromosomal in situ suppression (CISS) hybridization and R-banding.

Chromosomal in situ suppression (CISS) hybridization was used to investigate the distribution of material of chromosomes 1 and 5 present in marker chromosomes of Namalva cells. The Namalva cell line, established from a Burkitt's lymphoma, exhibits a highly variable female karyotype with a large number of marker chromosomes. Libraries from sorted human chromosomes 1 and 5 were used to delineate material of these chromosomes present in the Namalva karyotype. We used the DAB/peroxidase reaction and reflection contrast microscopy for detection of biotinylated hybrid molecules. Identification of chromosomes was achieved by fluorescent R-banding after CISS hybridization, which allowed the assignment of hybridized regions to the particular marker chromosomes. After CISS hybridization with a chromosome I library, the normal chromosome I was labelled as well as a large marker MI and the long arm of marker M3. Using a chromosome 5 library it could be shown that the distal part of the long arm of one chromosome 5 was translocated to marker M2. The normal chromosome 5 was completely labelled. The present investigation demonstrates the advantage of combining CISS hybridization and banding for the identification of complex, rearranged tumor karyotypes.