Wilson disease is a disorder of copper metabolism that can present with hepatic, neurologic, or psychiatric disturbances, or a combination of these, in individuals ranging from age three years to older than 50 years; symptoms vary among and within families. Liver disease includes recurrent jaundice, simple acute self-limited hepatitis-like illness, autoimmune-type hepatitis, fulminant hepatic failure, or chronic liver disease. Neurologic presentations include movement disorders (tremors, poor coordination, loss of fine-motor control, chorea, choreoathetosis) or rigid dystonia (mask-like facies, rigidity, gait disturbance, pseudobulbar involvement). Psychiatric disturbance includes depression, neurotic behaviors, disorganization of personality, and, occasionally, intellectual deterioration. Kayser-Fleischer rings, frequently present, result from copper deposition in Descemet's membrane of the cornea and reflect a high degree of copper storage in the body.

Xanthinuria, which was first described by Dent and Philpot (1954), is characterized by excretion of large amounts of xanthine in the urine and a tendency to form xanthine stones. Uric acid is strikingly diminished in serum and urine. Two clinically similar but distinct forms of xanthinuria are recognized. In type I (XAN1) there is an isolated deficiency of xanthine dehydrogenase, and in type II (XAN2; 603592) there is a dual deficiency of xanthine dehydrogenase and aldehyde oxidase (603592). Type I patients can metabolize allopurinol, whereas type II patients cannot (Simmonds et al., 1995). Xanthinuria also occurs in molybdenum cofactor deficiency (252150). Type II xanthinuria is caused by mutation in the MOCOS gene (613274), which encodes the enzyme that sulfurates the molybdenum cofactor for XDH and AOX1 (602841).

Purine nucleoside phosphorylase deficiency is a rare autosomal recessive immunodeficiency disorder characterized mainly by decreased T-cell function. Some patients also have neurologic impairment (review by Aust et al., 1992).

Renal hypouricemia is characterized by impaired uric acid reabsorption at the apical membrane of proximal renal tubule cells. The syndrome is not lethal and may be asymptomatic. However, it is accompanied by nephrolithiasis and exercise-induced acute renal failure in about 10% of patients (Ichida et al., 2008). Genetic Heterogeneity of Renal Hypouricemia See also RHUC2 (612076), which is caused by mutation in the SLC2A9 gene (606142).

Molybdenum cofactor deficiency (MoCD) represents a spectrum, with some individuals experiencing significant signs and symptoms in the neonatal period and early infancy (termed early-onset or severe MoCD) and others developing signs and symptoms in childhood or adulthood (termed late-onset or mild MoCD). Individuals with early-onset MoCD typically present in the first days of life with severe encephalopathy, including refractory seizures, opisthotonos, axial and appendicular hypotonia, feeding difficulties, and apnea. Head imaging may demonstrate loss of gray and white matter differentiation, gyral swelling, sulci injury (typically assessed by evaluating the depth of focal lesional injury within the sulci), diffusely elevated T2-weighted signal, and panlobar diffusion restriction throughout the forebrain and midbrain with relative sparring of the brain stem. Prognosis for early-onset MoCD is poor, with about 75% succumbing in infancy to secondary complications of their neurologic disability (i.e., pneumonia). Late-onset MoCD is typically characterized by milder symptoms, such as acute neurologic decompensation in the setting of infection. Episodes vary in nature but commonly consist of altered mental status, dystonia, choreoathetosis, ataxia, nystagmus, and fluctuating hypotonia and hypertonia. These features may improve after resolution of the inciting infection or progress in a gradual or stochastic manner over the lifetime. Brain imaging may be normal or may demonstrate T2-weighted hyperintense or cystic lesions in the globus pallidus, thinning of the corpus callosum, and cerebellar atrophy.

Molybdenum cofactor deficiency (MoCD) represents a spectrum, with some individuals experiencing significant signs and symptoms in the neonatal period and early infancy (termed early-onset or severe MoCD) and others developing signs and symptoms in childhood or adulthood (termed late-onset or mild MoCD). Individuals with early-onset MoCD typically present in the first days of life with severe encephalopathy, including refractory seizures, opisthotonos, axial and appendicular hypotonia, feeding difficulties, and apnea. Head imaging may demonstrate loss of gray and white matter differentiation, gyral swelling, sulci injury (typically assessed by evaluating the depth of focal lesional injury within the sulci), diffusely elevated T2-weighted signal, and panlobar diffusion restriction throughout the forebrain and midbrain with relative sparring of the brain stem. Prognosis for early-onset MoCD is poor, with about 75% succumbing in infancy to secondary complications of their neurologic disability (i.e., pneumonia). Late-onset MoCD is typically characterized by milder symptoms, such as acute neurologic decompensation in the setting of infection. Episodes vary in nature but commonly consist of altered mental status, dystonia, choreoathetosis, ataxia, nystagmus, and fluctuating hypotonia and hypertonia. These features may improve after resolution of the inciting infection or progress in a gradual or stochastic manner over the lifetime. Brain imaging may be normal or may demonstrate T2-weighted hyperintense or cystic lesions in the globus pallidus, thinning of the corpus callosum, and cerebellar atrophy.

Molybdenum cofactor deficiency (MoCD) represents a spectrum, with some individuals experiencing significant signs and symptoms in the neonatal period and early infancy (termed early-onset or severe MoCD) and others developing signs and symptoms in childhood or adulthood (termed late-onset or mild MoCD). Individuals with early-onset MoCD typically present in the first days of life with severe encephalopathy, including refractory seizures, opisthotonos, axial and appendicular hypotonia, feeding difficulties, and apnea. Head imaging may demonstrate loss of gray and white matter differentiation, gyral swelling, sulci injury (typically assessed by evaluating the depth of focal lesional injury within the sulci), diffusely elevated T2-weighted signal, and panlobar diffusion restriction throughout the forebrain and midbrain with relative sparring of the brain stem. Prognosis for early-onset MoCD is poor, with about 75% succumbing in infancy to secondary complications of their neurologic disability (i.e., pneumonia). Late-onset MoCD is typically characterized by milder symptoms, such as acute neurologic decompensation in the setting of infection. Episodes vary in nature but commonly consist of altered mental status, dystonia, choreoathetosis, ataxia, nystagmus, and fluctuating hypotonia and hypertonia. These features may improve after resolution of the inciting infection or progress in a gradual or stochastic manner over the lifetime. Brain imaging may be normal or may demonstrate T2-weighted hyperintense or cystic lesions in the globus pallidus, thinning of the corpus callosum, and cerebellar atrophy.

Xanthinuria type II (XAN2) is an autosomal recessive inborn error of metabolism resulting from a defect in the synthesis of the molybdenum cofactor, which is necessary for the 2 enzymes that degrade xanthine: XDH (607633) and AOX1 (602841). Most individuals with type II xanthinuria are asymptomatic, but some develop urinary tract calculi, acute renal failure, or myositis due to tissue deposition of xanthine. Laboratory studies show increased serum and urinary hypoxanthine and xanthine and decreased serum and urinary uric acid (summary by Ichida et al., 2001). Two clinically similar but distinct forms of xanthinuria are recognized. In type I xanthinuria (XAN1; 278300), there is an isolated deficiency of xanthine dehydrogenase resulting from mutation in the XDH gene; in type II, there is a dual deficiency of xanthine dehydrogenase and aldehyde oxidase. Type I patients can metabolize allopurinol, whereas type II patients cannot (Simmonds et al., 1995).

Renal hypouricemia is a common inherited disorder characterized by impaired renal urate reabsorption and subsequent low serum urate levels. It may be associated with severe complications such as exercise-induced acute renal failure (EIARF) and nephrolithiasis (summary by Matsuo et al., 2008). For additional phenotypic information and a discussion of genetic heterogeneity of renal hypouricemia, see RHUC1 (220150).

Fanconi-Bickel syndrome is a rare but well-defined clinical entity, inherited in an autosomal recessive mode and characterized by hepatorenal glycogen accumulation, proximal renal tubular dysfunction, and impaired utilization of glucose and galactose (Manz et al., 1987). Because no underlying enzymatic defect in carbohydrate metabolism had been identified and because metabolism of both glucose and galactose is impaired, a primary defect of monosaccharide transport across the membranes had been suggested (Berry et al., 1995; Fellers et al., 1967; Manz et al., 1987; Odievre, 1966). Use of the term glycogenosis type XI introduced by Hug (1987) is to be discouraged because glycogen accumulation is not due to the proposed functional defect of phosphoglucomutase, an essential enzyme in the common degradative pathways of both glycogen and galactose, but is secondary to nonfunctional glucose transport.

Any Fanconi syndrome in which the cause of the disease is a mutation in the HNF4A gene.