Adult Hypophosphatasia with a Single Heterozygous c.572A>G p.Glu191Gly Mutation in the ALPL gene: Case Report

Adult-onset hypophosphatasia manifests after age 18, and is characterized by reduced tissue-nonspecific alkaline phosphatase (ALP) activity. This can lead to fractures, pseudo-fractures, osteomalacia, decreased bone density (bone loss), muscle weakness, myalgia, arthralgia, headache, dental symptoms (loss of permanent teeth, periodontal disease), and pseudogout. Over 480 distinct genetic mutations have been identified to date, with eight cases reported for the c.572A>G (p.Glu191Gly) mutation. However, all reported cases involved compound heterozygous mutations, and there have been no previous reports of cases of a single heterozygous mutation. We report the case of a 40-year-old woman with persistent hypophosphatasia, elevated urinary phosphoethanolamine levels suggesting adult-onset hypophosphatasia, and a heterozygous missense mutation (c.572A>G p.Glu191Gly) in the ALPL gene according to genetic testing. Treatment with subcutaneous injections of aspartate phosphatase alpha was initiated, which was followed by significant improvement of the pain, enhanced range of motion in both upper limbs, and improved gait. This patient's case differed from previously reported cases in that it involved a heterozygous c.572A>G (p.Glu191Gly) mutation alone in adult-onset hypophosphatasia. Adult-onset hypophosphatasia is an extremely rare disorder. However, its symptoms resemble those of systemic rheumatic diseases such as polymyalgia rheumatica and fibromyalgia, and rheumatologists may encounter this condition in routine clinical practice. Importantly, it can be detected based on low serum ALP levels.