The diagnosis of hypophosphatasia in children as a multidisciplinary effort: an expert opinion.

Hypophosphatasia (HPP) is a rare genetic disorder in which pathogenic variants of the ALPL gene lead to a marked decrease of tissue non-specific alkaline phosphatase (TNSALP) activity. Although HPP is a systemic disorder, its clinical manifestations are more evident on bones, teeth, muscle and central nervous system. The clinical spectrum ranges from severe forms with extreme skeletal deformities, respiratory impairment, seizures, to very mild forms with onset in late adulthood and few clinical signs. The diagnosis can be suspected by measurement of TNSALP activity, but the insufficient awareness among health professionals and the lack of official guidelines are responsible for delayed diagnosis in children with HPP. The purpose of the current document is to provide an expert opinion directed at optimizing the diagnostic pathway of pediatric HPP. From April to December 2022, a multidisciplinary working group of 6 experts including two pediatric endocrinologists, a pediatric neurologist, a pediatric odontologist, a clinical geneticist, and a molecular biologist gathered in a series of periodic meetings to discuss the main issues related to the diagnosis of HPP in children and formalize an Expert Opinion statement. The experts agreed on a diagnostic trail that begins with the recognition of specific clinical signs, leading to biochemical analyses of TNSALP activity and vitamin B6 serum concentration. Very important are the neurological and dental manifestation of the disease that should be thoroughly investigated. The evaluation of TNSALP activity must consider sex and age variability and low activity must be persistent. Repeated blood measurements are thus necessary. The molecular analysis is then mandatory to confirm the diagnosis and for genetic counseling.