Osteonecrosis in genetic disorders

The avascular necrosis of bone is characterized by an abnormality of tissue that can occur whenever a disease process causes major cell stress. Some evidence supports a role for genetic factors in some avascular necrosis suggesting that gene mutations could play a role in the pathogenesis of osteonecrosis. These genetic studies provide hope that tools for identifying high risk patients will be available in the future

Genetic aspects of Paget’s disease of bone

Paget’s disease of bone (PDB) is a metabolic bone disease characterized by excessive bone resorption and formation due to increased osteoclasts activity. PDB mostly runs asymptomatically, although increased bone turnover can be present and in approximately 30% of patients bone abnormalities, such as bone pain and deformities, pathological fractures and deafness may occur. The existence of familial aggregation of PDB has been reported in numerous papers, describing the occurrence of disease in successive generations. It has been clearly established that PDB is genetically heterogeneous with several loci able to confer an increased susceptibility to develop this bone metabolic disorder. In particular, the PDB3 locus in chromosome 5q35-qter hosts the sequestosome1/ p62 (SQSTM1/p62) gene whose mutations account for most of the sporadic and familial forms of PDB reported in literature. SQSTM1/p62 gene encodes the SQSTM1/p62 protein, component of the NF-kB signaling pathway and mediating intracellular signaling from IL-1/TNF toward NF-kB, crucial for osteoclast differentiation and activity. A functional study suggests that the S Q S T M 1 mutation may predispose to PDB affecting the interaction between SQSTM1/p62 protein and a hitherto unidentified protein(s) modulating the bone turnover, but the underlying molecular mechanism need to be elucidated. However, independently from the knowledge of the functional aspects of S Q S T M 1 / p 6 2 mutation, the opportunity to perform germline mutational analysis in PDB patients may be helpful in detecting new genetic carriers in potentially familial forms of PDB and in studying the co-segregation of such DNA variants with the PDB phenotype. All together these studies could open new possibilities in the prevention and therapy of PDB and of other metabolic bone disorder

Pharmacogenetics of bisphosphonate-associated osteonecrosis of the jaw.

An undesirable effect associated with bisphosphonates is osteonecrosis of the jaw (ONJ). Case reports discussed ONJ development in patients with multiple myeloma or metastatic cancers receiving bisphosphonates as palliation for malignant bone disease. No causative relationship has been unequivocally demonstrated between ONJ and bisphosphonate therapy. To determine if a higher sensitivity to bisphosphonates could in part explain the development of ONJ, the segregation of A/C rs2297480 polymorphism of gene encoding for the farnesyl pyrophosphate synthase (FDPS) with ONJ was evaluated in a cohort of 68 Caucasian patients treated with zoledronic acid for multiple myeloma and metastatic mammary and prostate cancer. The AA and CC genotypes were highly differently distributed among ONJ patients and controls, matched for sex and type of malignant disease, with a positive correlation between AA carrier status and occurrence of ONJ (p=0.03) after 18-24 months of treatment. Because FDPS gene variants have been associated with bone morbidity, these pharmacogenetic association likely reflect the interaction of amino-bisphosphonates with germline sensitivity to drug actions, and might identify patients at highest risk to develop ONJ

Multiple endocrine neoplasia type 1

Multiple Endocrine Neoplasia type 1 (MEN1) is a rare autosomal dominant hereditary cancer syndrome presented mostly by tumours of the parathyroids, endocrine pancreas and anterior pituitary, and characterised by a very high penetrance and an equal sex distribution. It occurs in approximately one in 30,000 individuals. Two different forms, sporadic and familial, have been described. The sporadic form presents with two of the three principal MEN1-related endocrine tumours (parathyroid adenomas, entero-pancreatic tumours and pituitary tumours) within a single patient, while the familial form consists of a MEN1 case with at least one first degree relative showing one of the endocrine characterising tumours. Other endocrine and non-endocrine lesions, such as adrenal cortical tumours, carcinoids of the bronchi, gastrointestinal tract and thymus, lipomas, angiofibromas, collagenomas have been described. The responsible gene, MEN1, maps on chromosome 11q13 and encodes a 610 aminoacid nuclear protein, menin, with no sequence homology to other known human proteins. MEN1 syndrome is caused by inactivating mutations of the MEN1 tumour suppressor gene. This gene is probably involved in the regulation of several cell functions such as DNA replication and repair and transcriptional machinery. The combination of clinical and genetic investigations, together with the improving of molecular genetics knowledge of the syndrome, helps in the clinical management of patients. Treatment consists of surgery and/or drug therapy, often in association with radiotherapy or chemotherapy. Currently, DNA testing allows the early identification of germline mutations in asymptomatic gene carriers, to whom routine surveillance (regular biochemical and/or radiological screenings to detect the development of MEN1-associated tumours and lesions) is recommended