HYPOPHOSPHATASIA
Hypophosphatasia is an inborn error of metabolism characterized clinically by premature tooth loss and rickets or osteomalacia, and biochemically by subnormal serum alkaline phosphatase activity.72 Delineation of this condition has shown that alkaline phosphatase functions importantly as an ectoenzyme in skeletal mineralization. Four clinical forms, classified according to the patient’s age when skeletal disease is first noted (perinatal, infantile, childhood, adult), are generally reported. Actually, the severity of hypophosphatasia is a continuum that ranges from stillbirth to hypophosphatasemia in asymptomatic adults with unremarkable radiologic and histopathologic studies of bone.73,74 When hypophosphatasia manifests at birth, it may be confused with a severe form of OI because of profound hypomineralization of the skeleton, or with cleidocranial dysplasia because of wide cranial sutures.5 If
the onset is within the first 6 months of life (infantile form), only hypotonia may be noted perinatally, but subsequently failure to thrive may occur as patients develop clinically apparent rickets and hypercalcemia, recurrent pneumonias, and sometimes seizures or periodic apnea. Onset later in infancy or during childhood may cause short stature, rachitic deformity, early loss of deciduous teeth, and premature cranial synostosis.72,73 In the adult form, a history of dental disease often precedes painful recurrent stress fractures in the feet and pseudofractures (Looser zones) in the proximal femora.74 The severe forms are inherited as autosomal recessive traits.72 The adult form can be transmitted as an autosomal dominant trait, but with variable penetrance.74 Odontohypophosphatasia refers to the disorder in patients (primarily children) who have only dental manifestations. More than 58 different mutations in the gene that encodes the isoenzyme form of alkaline phosphatase found in bone have been detected in individuals with hypophosphatasia.75
the onset is within the first 6 months of life (infantile form), only hypotonia may be noted perinatally, but subsequently failure to thrive may occur as patients develop clinically apparent rickets and hypercalcemia, recurrent pneumonias, and sometimes seizures or periodic apnea. Onset later in infancy or during childhood may cause short stature, rachitic deformity, early loss of deciduous teeth, and premature cranial synostosis.72,73 In the adult form, a history of dental disease often precedes painful recurrent stress fractures in the feet and pseudofractures (Looser zones) in the proximal femora.74 The severe forms are inherited as autosomal recessive traits.72 The adult form can be transmitted as an autosomal dominant trait, but with variable penetrance.74 Odontohypophosphatasia refers to the disorder in patients (primarily children) who have only dental manifestations. More than 58 different mutations in the gene that encodes the isoenzyme form of alkaline phosphatase found in bone have been detected in individuals with hypophosphatasia.75
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