Recurrent Metatarsal Fractures in Postmenopausal Woman With Low Serum Alkaline Phosphatase: A Rare Diagnosis Not to Miss

Hypophosphatasia (HPP) is a rare inborn error of metabolism due to a loss-of-function mutation in the gene for tissue nonspecific isoenzyme of alkaline phosphatase (ALP) that results in low levels of ALP. The clinical presentation of HPP is variable and in adults can easily be misdiagnosed as other forms of osteomalacia. We present a case of a 53-year-old Caucasian female who was evaluated for recurrent metatarsal fractures. She reported her first metatarsal fracture at age 21, and since then had at least 8 more metatarsal fractures over her lifetime, most without injury other than weight bearing. She reported history of gait disturbance as a child and dental issues (spacing and loosening). Laboratory tests showed normal serum calcium, phosphorus, and parathyroid hormone, but low serum ALP