THU432 Severe Osteoporosis Associated With A Novel Plastin 3 (PLS3) Mutation

Disclosure: A. Ibrahim: None. L. Esper: None. S.M. Gandhi: None. E.S. Nylen: None. Early Onset Osteoporosis (EOOP) affects children and young adults and can be caused by endocrinopathies, chronic medical conditions, nutritional deficiencies, and/or genetic mutations. The most common inherited cause is osteogenesis imperfecta(OI), and a rare variant linked to OI includes a defect in the X chromosomal gene encoding Plastin 3 (PLS3). In our case, a 34-year-old male was referred for severe osteoporosis. He had been diagnosed with osteopenia at age 21. At age 24, imaging revealed multiple vertebral compression fractures and DXA scan confirmed severe osteoporosis. He required L3-L5 kyphoplasty and started on oral bisphosphonates for presumed OI despite negative gene mutation (i.e., COL1A1/COL1A2). He continued treatment for only 2 years. 8 years later, he had persistent osteoporosis (DXA L2-4 Z-score -3.6, LFN Z-score -3.2). He had no evidence of kyphosis or scoliosis and no extraskeletal manifestations such as blue-grey sclera or any dysmorphic features. The workup was negative for secondary causes of EOOP and he denied a family history of osteoporosis. Labs showed normal 24-hour urine calcium, bone markers, and bone Alkaline Phosphatase. Karyotyping showed normal XY and gene analysis was again negative for OI. He started treatment with intravenous Zoledronic acid, however, had a 2-year gap between doses initially causing BMD to drop by 6.5% in L2-L4 (Z -4.1) and by 5.7% in LFN (Z -3.1). Subsequently, he received a total of 5 doses of Zoledronic acid to date and had no further fractures. DXA significantly improved by 10.4% in L2-4 (Z -2.6), and 16.3% in LFN (Z -2.0). Repeated expanded gene testing showed a novel PLS3 hemizygous mutation (deletion at site C.234_237+10del of Exon 3). This case demonstrates a novel PLS3 mutation variant to be a plausible cause of adulthood EOOP which was responsive to bisphosphonate treatment. PLS3 is an F-actin binding and bundling protein involved in cytoskeletal remodeling and may have roles in calcium homeostasis, cell migration, endocytosis, DNA repair, and membrane trafficking. Currently, less than 30 loss of function variants of PLS3 have been identified and all lead to severe osteoporosis- particularly in children. However, our patient’s known onset of bone loss occurred much later- in his twenties and he had no evidence of extra-skeletal manifestations. The cause for such late presentation is unclear but may be attributed to this specific variant of PLS3. This case highlights that PLS3 mutation should be on the differential for EOOP even in early adulthood. Our patient’s BMD has markedly improved with bisphosphonates and he sustained no further fractures after starting therapy. Timely diagnosis and earlier detection will allow for appropriate genetic counseling, earlier screening, and treatment of affected family members. Presentation: Thursday, June 15, 2023