Clinical spectrum of hypophosphatasia diagnosed in adults

The presentation of hypophosphatasia (HPP) diagnosed in adults demonstrates a wide range of clinical manifestations, many of which are nonspecific. We sought to assess clinical characteristics of adult HPP by evaluation of Mayo Clinic Rochester adults diagnosed with HPP from 1976 through 2008. Subjects were identified by diagnostic code or medical records. Inclusion criteria were age ≥18 years at diagnosis; low serum alkaline phosphatase (AP) without bisphosphonate therapy; and one additional element: elevated pyridoxal 5'-phosphate (PLP) or urine phosphoethanolamine (PEA), evidence of osteomalacia, or family history. We were unable to distinguish manifesting carriers from silent unaffected carriers due to lack of a prospective standardized clinical evaluation and the absence of genetic testing. HPP was diagnosed in 22 unrelated adults (median age 49 years; 68% women). Most patients (68%) were symptomatic at presentation with features including musculoskeletal pain (41%) or incident fracture (18%). A history of fracture was present in 54%: hip/femoral neck (23%), feet (23%, all women), wrist (18%), and spine (9%, all men). Nine patients (36%) had multiple fractures while 4 (all women) had subtrochanteric femur fractures. Radiographic chondrocalcinosis (27%) and documented pyrophosphate arthropathy (14%) were only observed in women. Median minimum serum AP was 43% below the lower normal limit. Urine PEA was elevated in 15/16 patients (94%). PLP median was 68 μg/L (normal, 5-50 μg/L) and all (n=8) were above normal. Symptomatic subjects had more fractures and chondrocalcinosis, lower median minimum AP and PLP and higher median PEA levels. Clinical features more common in fracture patients included symptoms at presentation, history of childhood rickets, dental abnormalities, lower median minimum AP and PLP, and higher median urine PEA. Four subjects had iliac crest bone biopsies, with 2/4 specimens consistent with osteomalacia. These results suggest that adult HPP demonstrates a wide spectrum of clinical manifestations including musculoskeletal pain, fractures, chondrocalcinosis and dental anomalies with some overlap in laboratory characteristics in relationship to disease severity. In addition to genetic and environmental factors, gender may influence the clinical expression of HPP.