Weaving bone resilience: a case of co-occurrence of osteogenesis imperfecta and hypophosphatasia

This report describes the genetic and clinical findings of a rare case of osteogenesis imperfecta (OI) and hypophosphatasia (HPP) occurring simultaneously in an adult patient. OI is a rare inherited disease that primarily affects the skeleton, reducing bone mass and causing fractures. About 85% of OI cases are caused by autosomal dominant mutations in either COL1A1 or COL1A2. HPP, also a rare genetic disorder, is caused by pathogenic variants in the ALPL gene, leading to deficient activity of tissue-nonspecific alkaline phosphatase and causing defective mineralization of bone. We describe the case of a 63-year-old female patient with a dual diagnosis of OI and HPP. This patient was initially treated with bisphosphonates with some benefit. However, she presented new fractures, and decreased levels of alkaline phosphatase (ALP) were noted. Two heterozygous variants, in COL1A1 and ALPL, were identified. After the genetic results, we decided to stop bisphosphonate treatment and start her on teriparatide. Since then, no fractures have occurred, and her ALP levels have normalized. This report details a rare case of a woman co-diagnosed with OI and HPP, illustrating the genetic and clinical manifestations of both conditions. Initially treated with bisphosphonates, the patient experienced new fractures. Following molecular insights, transitioning to teriparatide resulted in no further fractures and normalization of her ALP levels. KEY WORDS: Osteogenesis imperfecta, hypophosphatasia, osteoporosis, bone fractures.