Multifocal osteonecrosis due to the synergistic impact of inherited thrombophilia, autoimmunity and pregnancy: a case report.

Multifocal osteonecrosis is a rare entity which can lead to bone fragility, fractures and considerable morbidity. The objective of this report is to describe the presentation, evaluation and management of a case of multifocal osteonecrosis. A 34-year-old lady presented with multiple fractures and bone pain which was exacerbated during pregnancy. She was found to have osteonecrosis involving multiple sites. Investigation revealed that she had an undefined autoimmune condition with antinuclear antibody and anti-Ro (SS-A) positivity, not fulfilling criteria for diagnosis of Sjogren syndrome. She had low Protein S levels for age and gender (confirmed on 2 occasions 12 weeks apart outside pregnancy). She had a novel variant in the PROS1 gene (NM_000313.4:c.1513G>A; p.Gly505Ser) which is associated with heterozygous Protein S (PS) deficiency. She had a good response to treatment with anticoagulation. The combination of inherited thrombophilia, autoimmunity and the thrombophilic state induced by pregnancy probably contributed to the severe phenotype in this patient. The variant was identified in the Lamin G1 domain, which is instrumental in PS binding to tissue factor pathway inhibitor and C4 binding protein, thus playing a role in both the coagulation and complement pathway, and could explain the coexistence of autoimmunity with thrombophilia. This variant is present in 0.034% of South Asians in the gnomAD population database, and may represent an important cause of inherited thrombophilia in this group.