Hypophosphatasia is characterized by defective mineralization of growing or remodeling bone, with or without root-intact tooth loss, in the presence of low activity of serum and bone alkaline phosphatase. Clinical features range from stillbirth without mineralized bone at the severe end to pathologic fractures of the lower extremities in later adulthood at the mild end. While the disease spectrum is a continuum, seven clinical forms of hypophosphatasia are usually recognized based on age at diagnosis and severity of features: Perinatal (severe): characterized by pulmonary insufficiency and hypercalcemia. Perinatal (benign): prenatal skeletal manifestations that slowly resolve into one of the milder forms. Infantile: onset between birth and age six months of clinical features of rickets without elevated serum alkaline phosphatase activity. Severe childhood (juvenile): variable presenting features progressing to rickets. Mild childhood: low bone mineral density for age, increased risk of fracture, and premature loss of primary teeth with intact roots. Adult: characterized by stress fractures and pseudofractures of the lower extremities in middle age, sometimes associated with early loss of adult dentition. Odontohypophosphatasia: characterized by premature exfoliation of primary teeth and/or severe dental caries without skeletal manifestations.

Acrodermatitis enteropathica of the zinc deficiency type (AEZ) is characterized by intermittent simultaneous occurrence of diarrhea and dermatitis with failure to thrive. Alopecia of the scalp, eyebrows, and eyelashes is a usual feature. The skin lesions are bullous. Noteworthy is the cure by diodoquin, or diiodohydroxyquinoline (Dillaha et al., 1953; Bloom and Sobel, 1955). Rodin and Goldman (1969) described autopsy findings, including pancreatic islet hyperplasia, absence of the thymus and of germinal centers, and plasmocytosis of lymph nodes and spleen.

Hypophosphatasia is characterized by defective mineralization of growing or remodeling bone, with or without root-intact tooth loss, in the presence of low activity of serum and bone alkaline phosphatase. Clinical features range from stillbirth without mineralized bone at the severe end to pathologic fractures of the lower extremities in later adulthood at the mild end. While the disease spectrum is a continuum, seven clinical forms of hypophosphatasia are usually recognized based on age at diagnosis and severity of features: Perinatal (severe): characterized by pulmonary insufficiency and hypercalcemia. Perinatal (benign): prenatal skeletal manifestations that slowly resolve into one of the milder forms. Infantile: onset between birth and age six months of clinical features of rickets without elevated serum alkaline phosphatase activity. Severe childhood (juvenile): variable presenting features progressing to rickets. Mild childhood: low bone mineral density for age, increased risk of fracture, and premature loss of primary teeth with intact roots. Adult: characterized by stress fractures and pseudofractures of the lower extremities in middle age, sometimes associated with early loss of adult dentition. Odontohypophosphatasia: characterized by premature exfoliation of primary teeth and/or severe dental caries without skeletal manifestations.

Hypophosphatasia is characterized by defective mineralization of growing or remodeling bone, with or without root-intact tooth loss, in the presence of low activity of serum and bone alkaline phosphatase. Clinical features range from stillbirth without mineralized bone at the severe end to pathologic fractures of the lower extremities in later adulthood at the mild end. While the disease spectrum is a continuum, seven clinical forms of hypophosphatasia are usually recognized based on age at diagnosis and severity of features: Perinatal (severe): characterized by pulmonary insufficiency and hypercalcemia. Perinatal (benign): prenatal skeletal manifestations that slowly resolve into one of the milder forms. Infantile: onset between birth and age six months of clinical features of rickets without elevated serum alkaline phosphatase activity. Severe childhood (juvenile): variable presenting features progressing to rickets. Mild childhood: low bone mineral density for age, increased risk of fracture, and premature loss of primary teeth with intact roots. Adult: characterized by stress fractures and pseudofractures of the lower extremities in middle age, sometimes associated with early loss of adult dentition. Odontohypophosphatasia: characterized by premature exfoliation of primary teeth and/or severe dental caries without skeletal manifestations.

The phenotypic spectrum of lysosomal acid lipase (LAL) deficiency ranges from the infantile-onset form (Wolman disease) to later-onset forms collectively known as cholesterol ester storage disease (CESD). Wolman disease is characterized by infantile-onset malabsorption that results in malnutrition, storage of cholesterol esters and triglycerides in hepatic macrophages that results in hepatomegaly and liver disease, and adrenal gland calcification that results in adrenal cortical insufficiency. Unless successfully treated with hematopoietic stem cell transplantation (HSCT), infants with classic Wolman disease do not survive beyond age one year. CESD may present in childhood in a manner similar to Wolman disease or later in life with such findings as serum lipid abnormalities, hepatosplenomegaly, and/or elevated liver enzymes long before a diagnosis is made. The morbidity of late-onset CESD results from atherosclerosis (coronary artery disease, stroke), liver disease (e.g., altered liver function ± jaundice, steatosis, fibrosis, cirrhosis and related complications of esophageal varices, and/or liver failure), complications of secondary hypersplenism (i.e., anemia and/or thrombocytopenia), and/or malabsorption. Individuals with CESD may have a normal life span depending on the severity of disease manifestations.

DEE95 is a severe autosomal recessive developmental disorder characterized by severely impaired global development, hypotonia, weakness, ataxia, coarse facial features, and intractable seizures. More variable features may include abnormalities of the hands and feet, inguinal hernia, and feeding difficulties. The disorder is part of a group of similar neurologic disorders resulting from biochemical defects in the glycosylphosphatidylinositol (GPI) biosynthetic pathway (summary by Nguyen et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

Neurodevelopmental disorder with hypotonia and cerebellar atrophy, with or without seizures (NEDHCAS) is an autosomal recessive neurodevelopmental disorder characterized by global developmental delay with variably impaired intellectual development, delayed motor skills, and poor or absent speech. Most patients develop early-onset seizures and demonstrate cerebellar ataxia or dysmetria associated with progressive cerebellar atrophy on brain imaging. The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis (summary by Nguyen et al., 2020). For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

Glycosylphosphatidylinositol biosynthesis defect-25 (GPIBD25) is an autosomal recessive neurodevelopmental disorder characterized by global developmental delay, brain anomalies, hypotonia, and contractures (Salian et al., 2022). For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).