THU457 Variable Presentations Of Hypophosphatasia In Two Patients In The Outpatient Setting

Disclosure: A. Elmaaz: None. S. Batool: None. P. Dandona: None. Introduction: Hypophosphatasia is a rare disorder characterized by defective mineralization of bone and teeth which is caused by an autosomal inherited mutation in the tissue nonspecific alkaline phosphatase (ALP) encoding genes. Here we present two cases of multiple dental and bony defects secondary to low ALP enzyme activity due to hypophosphatasia. Case 1: A 27-year-old female with history of mitochondrial disease, gastroparesis, malabsorption syndrome, and autonomic dysfunction was referred to Endocrinology clinic because of persistently low serum ALP levels associated with recurrent muscle, joint, and bone pain since the age of 13. She had history of multiple tooth extractions because of dental developmental abnormalities and fractures. She also reported history of fractures of three of her fingers in both hands during her childhood and teenage years. The patient was adopted and was unaware of any biological family history. Physical examination was remarkable for short-statured female, 4'8". Notably, the middle phalanges in little fingers bilaterally were shorter than the other fingers. Workup showed vitamin D level of 21 (30-80) ng/ml, despite being on 50,000 IU twice a week for 6 months with normal PTH and ionized calcium levels. The repeated serum level of ALP was 24 (31-125) U/L with bone and liver isoenzymes levels of 42% and 58 % respectively. Vitamin B6 level was 13.2 (2.1-21.7) ng/ml. Bone mineral density was unremarkable. Case 2: A 53-year-old female with history of congenital left hip dysplasia, hypertension, and dyslipidemia was seen by Endocrinology service for evaluation of decreased ALP levels. She denied any history of falls or fractures. However, she reported chronic bone pain, especially in bilateral hip joints with history of multiple surgeries in her left hip joint. She had required teeth braces and multiple dental surgeries during her childhood due to dental maldevelopment. Her height was 4'8". Laboratory workup was remarkable for low serum ALP level of 30 U/L with bone isoenzyme of 24 %. Vitamin B6 level was 206.7 (2.1-21.7) ng/ml. She had elevated serum phosphorus levels with normal calcium, PTH, and vitamin D levels. Pyridoxal-5- Phosphate level was high. Bone mineral density revealed osteopenia. Conclusion: Hypophosphatasia is a rare disease, hence it could be easily missed due to high variability in clinical presentations and severity of symptoms. Low serum levels of ALP with history of bone pain, recurrent fractures, premature loss of deciduous teeth, or loss of adult dentition should raise the suspicion of hypophosphatasia. Resistance to vitamin D supplementation is another clue to the diagnosis. A multidisciplinary approach is required for appropriate management. Presentation: Thursday, June 15, 2023