Severe neurological symptoms, i.e., fatal encephalopathy, have been reported for a patient suffering from perinatal HPP with a complete lack of TNAP activity as two compound heterozygous mutations were detected in the ALPL gene, thereby highlighting the role of the enzyme during the neurological development in humans [147] (see also chapter “Neurological symptoms of HPP”). The gene discussed is ALPL; the disease is Encephalopathy.