Disorders of amino-acid transport and metabolism
- disorders affecting amino acid metabolism; majority of these disorders are inherited and present in the neonatal period with metabolic disturbances (for example, acidosis) and neurologic manifestations; present at birth, although they may not become symptomatic until later in life.
Disturbances of amino-acid transport
- lysosomal storage disorders of unknown molecular defect, characterized by widespread deposition of cystine crystals in reticuloendothelial cells.
- An autosomal recessive hereditary disorder characterized by defective transportation of cystine across the lysosomal membranes and systemic deposition of cystine crystals in the body. It is associated with slight increase of the plasma cystine, cystinuria, aminoaciduria, glycosuria, polyuria, hypophosphatemia, rickets, and renal tubular dysfunction. --2004
- inherited abnormality of renal tubular transport of dibasic amino acids leading to massive urinary excretion of cystine, lysine, arginine, and ornithine.
- constellation of clinical and laboratory manifestations produced by generalized proximal tubular insufficiency in the presence of normal, or nearly normal, glomerular filtration.
- disorder of amino acid transport characterized by the childhood (or rarely adult) onset of photosensitive dermatitis and intermittent neurologic symptoms; ataxia, personality changes, migraine headaches, and photophobia may occur periodically; results from impaired sodium-dependent transport of neutral amino acids across the brush border membrane of the small intestine and renal tubular epithelium.
Phenylketonuria (pku)
- group of autosomal recessive disorders marked by a deficiency of the hepatic enzyme phenylaline hydroxylase or less frequently by reduced activity of dihydropteridine reductase.
- any of several autosomal recessive defects in the hydroxylation of phenylalanine resulting in accumulation and excretion of dietary phenylalanine; most commonly the defect is in the enzyme phenylalanine 4-monooxygenase; the most severe manifestation of this is classic PHENYLKETONURIA, but two benign forms also occur; rarely the defect is one of tetrahydrobiopterin metabolism.
Other disturbances of aromatic amino-acid metabolism
- general term for a number of inherited defects of amino acid metabolism in which there is a deficiency or absence of pigment in the eyes, skin, or hair.
- WHAT: Ochronosis. Ochronosis: the pathologic accumulation of a blue-black pigment in the connective tissues of persons with alkaptonuria, a rare inborn error of metabolism. These persons lack the enzyme homogentisic acid oxidase, resulting in a buildup of homogentisic acid, a precursor of the pigment. WHY: The great majority of patients with ochronosis eventually develop an arthropathy clinically resembling degenerative joint disease. HOW: Ochronosis is diagnosed by the combination of pigmentation of the cartilage, the presence of homogentisic acid in the urine, and arthritis usually involving the knees, hips, lumbosacral spine, and shoulders. The slate blue-black pigmentation is most apparent in the sclera of the eyes, the external ears, and the tympanic membranes. The cerumen may also show a dark discoloration. The presence of homogentisic acid in the urine is determined by the dark color which occurs when the urine is alkalinized and by paper chromatography. REFS: Schumacher HR and Holdsworth DE: Ochronotic arthropathy I. Clinico-pathologic Studies. Semin Arthritis Rheum 6:207, 1977. DN19296-1.
- rare, autosomal dominant disease with variable penetrance and several known clinical subtypes; characteristics may include depigmentation of the hair and skin, congenital deafness, heterochromia iridis, medial eyebrow hyperplasia, hypertrophy of the nasal root, and especially dystopia canthorum; the underlying cause may be defective development of the neural crest (neurocristopathy); may be closely related to piebaldism; Klein-Waardenburg Syndrome refers to a disorder that also includes upper limb abnormalities.
Disturbances of branched-chain amino-acid metabolism
- autosomal recessive inherited disorder with multiple forms of phenotypic expression, caused by a defect in the oxidative decarboxylation of branched-chain amino acids; metabolites accumulate in body fluids and render a "maple syrup" odor; divided into classic, intermediate, intermittent, and thiamine responsive subtypes; classic form presents in the first week of life with ketoacidosis, hypoglycemia, emesis, neonatal seizures, and hypertonia; the intermediate and intermittent forms present in childhood or later with acute episodes of ataxia and vomiting.
Disturbances of sulphur-bearing amino-acid metabolism
- autosomal recessive inborn error of methionine metabolism usually caused by a deficiency of cystathionine beta-synthase and associated with elevations of homocysteine in plasma and urine; clinical features include a tall, slender habitus, scoliosis, arachnodactyly, muscle weakness, genu varis, thin blond hair, malar flush, lens dislocations, an increased incidence of mental retardation, and a tendency to develop fibrosis of arteries, frequently complicated by cerebrovascular accidents and myocardial infarction.
Disturbances of histidine metabolism
- autosomal recessive aminoacidopathy due to deficiency of histidine ammonia-lyase; characterized by accumulation of histidine in serum and urinary excretion of histidine and metabolites, but is usually benign; may cause mild central nervous system dysfunction.
Disorders of urea cycle metabolism
- autosomal recessive aminoacidopathy characterized by marked elevation in plasma and urine levels of citrulline, with hyperammonemia and sometimes secondary oroticaciduria; clinical findings include mental retardation and neurologic abnormalities.
- excess of ornithine in the plasma, such as occurs in the genetic disorders gyrate atrophy of choroid and retina and hyperornithinemia-hyperamonemia-homocitrullinuria syndrome.
Other disturbances of straight-chain amino-acid metabolism
- autosomal recessive metabolic disorder caused by deficiencies in the mitochondrial glycine cleavage system; an enzyme system with four components: p-, t-, h-, and l-proteins; deficiency of the p-protein is the most prevalent form; clinical features include seizures, hypotonia, apnea, and coma; when the illness presents in childhood there tends to be an associated progressive dementia accompanied by extrapyramidal signs.
Other specified disorders of amino-acid metabolism
Unspecified disorder of amino-acid metabolism
- disorders affecting amino acid metabolism; majority of these disorders are inherited and present in the neonatal period with metabolic disturbances (for example, acidosis) and neurologic manifestations; present at birth, although they may not become symptomatic until later in life.
