ABSTRACT
Hypophosphatasia is a rare inherited disorder characterized by defective bone and teeth mineralization and deficiency of serum and bone alkaline phosphatase activity. Several mutations in the TNSALP gene are identified. The authors describe a Tunisian case having a mutation that has not been described up to now. It is about an infant, in the antecedents of recurring disease of the lungs in child since the age of seven months, which presents clinical and radiological signs of rickets. The diagnosis of hypophos-phatasia is strongly suspected in front of Reduced serum alkaline phosphatase activity and confirmed by the genetic study. The child is homozygous for a new mutation L282P in the ninth exon of the gene. The parents and two brother and sister are heterozygous for the same mutation