EXPRESS: Clinical and molecular findings in children and young adults with persistent low alkaline phosphatase levels.

BACKGROUND Hypophosphatasia is a rare inherited metabolic disease resulted by ALPL gene mutations. It is characterized by defective bone and teeth mineralization. The phenotypic spectrum is highly variable ranging from lethal perinatal form to mild forms which are only diagnosed in adulthood or remain undiagnosed despite persistently low levels of ALP. The aim of this study is to evaluate the clinical phenotype and frequency of ALPL mutations in a group of patient with hypophosphatasemia. METHODS Thirty individuals with alkaline phosphatase values below 40 IU/L in at least two assessments and having no alternative explanation for their low ALP levels were included in the study. The clinical features and radiological data of the study group were re-investigated for hypophosphatasia related findings. ALPL sequence analysis was performed using Sanger sequencing. RESULTS No patient in the study group had severe symptoms, nor had they initially been diagnosed as having hypophosphatasia. Four different heterozygous ALPL mutations (c.542C>T, c.648+1G>A, c.657G>T, and c.862+1G>C) were found in four patients. One splice site mutation (c.862+1G>C) was reported for the first time in this study. CONCLUSION ALPL sequence analysis may help to diagnosing genetic defects in indivuduals with persistently low ALP levels and provide to take preventive measures before symptoms appear. As in the other populations HPP displays allelic heterogeneity in our population.