MON-361 Late Diagnosis in Adult Form of Hypophosphatasia

INTRODUCTION/BACKGROUND: Hypophosphatasia is a rare inborn error of metabolism that presents with important foot and thigh pain due to stress fractures. The diagnose of the adult form is routinely neglected, even though it presents symptomatic and with persistent low serum alkaline phosphatase (ALP). CLINICAL CASE (DIAGNOSTIC EVALUATION, TRATMANET AND FUP): A 43-year-old amateur athlete woman presented with pain in the right femur without any local trauma. Physical examination evidenced prolonged right tight pain and no other findings. Bone mineral density evaluated by dual-energy x-ray absorptiometry was unremarkable. Biochemical investigations showed normal inorganic phosphate, calcium, zinc, and magnesium, but low ALP. The patient had six previous ALP measurements and all of them were below the lower limit of normality (46 a 116 U/L). These measurements were done in regular ob-gyn checkups with no further investigation or follow-up. In light of the hypophosphatasemia and pathologic fracture, the serum pyridoxal 5’-phosphate concentration was measured and found to be elevated 35,8 mcg/L (normal 5,0 a 30,0 mcg/L). CLINICAL LESSONS/CONCLUSION: Hypophosphatasia occurs due to a deactivating mutation (or mutations) of the gene encoding Tissue-Nonspecific Alkaline Phosphatase (TNSALP), leading to a global deficiency of TNSALP activity and inadequate skeletal mineralization and fractures. The adult form presents during middle age with stress fractures. The first complaints maybe foot pain, which is due to stress fractures of the metatarsals, and thigh pain, due to pseudo fractures of the femur. Our patient illustrates the importance of low serum ALP activity in the assessment of these patients. The correct diagnosis should help to avoid the use of traditional therapies for osteoporosis or osteomalacia, which would be ineffective or potentially harmful.