Amino acid metabolism disease

Introduction to Amino Acid Metabolic Diseases The amino acid metabolism disease is amino acidopathy, or amino aciduria. Can be divided into two categories: one is the enzyme defect, which makes the amino acid catabolism block, and the other is the defect of the amino acid absorption transport system. At least half of the 48 genetic amino acid diseases listed by Rosenberg and Scriver have significant neurological abnormalities, and the other 20 amino acid diseases cause defects in the kidney transport of amino acids, which can cause secondary nervous system damage. When the nervous system is involved, usually only mild mental motor developmental delay occurs, until after 2 to 3 years of onset, there are obvious symptoms. Like other hereditary metabolic diseases, amino acid disease does not affect the intrauterine growth, development or childbirth of the fetus. In the early stage, there are no signs. In addition to individual cases, amino acids are autosomal recessive, phenylketonuria (PKU), tyrosinemia and Hartnup disease are three important early childhood amino acid diseases. A typical disease caused by a biochemical defect. basic knowledge The proportion of illness: 0.001% Susceptible people: good in childhood Mode of infection: non-infectious Complications: cirrhosis, ataxia

Amino acid metabolic disease etiology

(1) Causes of the disease

Except in a few cases, amino acid metabolic diseases are autosomal recessive genetic diseases, and the offspring of close relatives are more common.

(two) pathogenesis

There are two main causes of amino acid metabolism diseases, namely, the lack of certain enzymes and the absorption barrier of amino acids. The former is known to be an enzyme or a certain lack or decrease of an enzyme activity, such as phenylalanine hydroxylation. Lack of enzyme causes phenylketonuria; lack or decrease of branched amino acid -keto acid decarboxylase causes maple syrup urine disease; isovalerate caused by lack of isovaleryl-CoA dehydrogenase; Homocysteine caused by cystathionine synthase deficiency; arginineemia caused by arginase deficiency; high lysineemia caused by lysine ketoglutarate reductase deficiency, etc. It is caused by the reverse of amino acid and malabsorption, and is often a barrier to the absorption of certain amino acids by the intestines or other tissues, such as liver-brain-kidney (Lowe) syndrome, Hartnup disease, and the like.

1. Hereditary tyrosinemia: is autosomal recessive, which encodes a defect in the gene of fumarylacetoacetate hydrolase on chromosome 15, resulting in the accumulation of tyrosine and metabolites.

2. Hartnup disease: It is caused by a defect in the transporter of neutral amino acids (such as mono-amino acid, mono-carboxyl amino acid, etc.). The causative gene of this protein is located on chromosome 2, and the female carries the disease-causing gene to the offspring due to tryptophan. (tryptophan) through the renal tubule transport disorder, resulting in increased excretion of these amino acids in urine and feces, a large amount of urine in the urine (indican), mainly indoxyl sulfate (indoxyl sulfate), especially eating a large amount of L-color ammonia After the acid food, the urine also contains a large amount of abnormal metabolites of non-hydroxylated hydrazine, which is lost due to the excretion of a large amount of tryptophan in the urine, which reduces the synthesis of niacin as a synthetic raw material, resulting in a change in the skin of the skin. The pathological basis of the disease has not been determined.

Amino acid metabolism prevention

Difficulties in the treatment of genetic diseases, unsatisfactory results, prevention is more important, preventive measures include avoiding close relatives marriage, implementation of genetic counseling, carrier genetic testing and prenatal diagnosis and selective abortion to prevent the birth of children.

Amino acid metabolic disease complications Complications cirrhosis ataxia

There are many kinds of amino acid metabolic diseases, and the clinical symptoms and signs are complex and diverse, and the performances outside the nervous system are different. For details, please refer to the clinical manifestations of each disease, and will not be described here.

Symptoms of Amino Acid Metabolism Symptoms Symptoms of tyrosinemia after half a year or after 1 year of age... Liver failure Ataxia palm and plantar keratosis with sweaty abdomen sag

At present, there are more than 100 genetic diseases caused by amino acid metabolism disorders. With the continuous advancement of biochemical detection technology, new discoveries will continue to increase, and amino acid metabolic diseases often lead to nervous system dysfunction. When the nervous system is involved, Usually only mild mental motor developmental delay occurs, and there are obvious symptoms until 2 to 3 years after the onset of the disease.

Like other hereditary metabolic diseases, amino acid disease does not affect the intrauterine growth, development or childbirth of the fetus, and there is no sign in the early stage. The main clinical features are normal appearance and activity at birth, and gradually decline after half a year or 1 year old, appropriate After a combination of amino acid supplementation, diet control, and vitamins, neurological symptoms can be improved in many cases.

1. Hereditary tyrosinemia or Richner-Hanhart disease is a rare dermatic amino acidopathy. The clinical manifestations are as follows:

(1) About half of the children have mild to moderate mental decline, may have self-mutilation behavior and uncoordinated performance of body movements, and language defects are more prominent. When 1 year old or 1 year old, corneal erosion often causes tearing. , photophobia and red eyes, new blood vessel formation and corneal opacity, palm and plantar keratosis with sweating and pain are common, is the inflammatory reaction nodules caused by crystalline tyrosine deposition, is also the cause of corneal lesions.

(2) may have liver, splenomegaly or cirrhosis, ascites and other liver failure manifestations, often died 1 year or years after the disease, neonatal tyrosinemia can cause liver failure and death, blood cheese The increase in the content of tyrosine and urinary tyrosine is diagnostic, and amino acids such as blood methionine (methionine) can also be increased.

2. Hartnup disease is a common amino acid disease of tryptophan transport disorder, named after the first family of diseases, the incidence rate is 1 / 24,000 live infants, the clinical manifestations are as follows:

(1) The child is normal at birth, with symptoms in the late stage of the baby or early childhood. The characteristic clinical manifestation is intermittent red scaly rash, covering the face, neck, hands and feet, which is similar to the lesion of pellagra.

(2) may have growth retardation, paroxysmal personality disorder such as emotional changes, can not control temper, mental disorder - hallucinatory psychosis, paroxysmal cerebellar ataxia (gait instability, intentional tremor and dysarthria, etc. ), occasionally there may be signs such as tendon, dizziness, nystagmus, diplopia and ptosis.

(3) Sun exposure, emotional stress response and taking sulfa drugs can trigger symptoms, and the attack lasts for about 2 weeks, followed by a relatively normal period of time. As the child matures, the frequency of attack decreases. Some children may have a mild persistent mental decline.

Examination of amino acid metabolic diseases

Hematuria is routine, liver function, blood amino acid content determination has diagnostic significance.

1. The content of blood tyrosine is increased in children with hereditary tyrosinemia, urinary tyrosine is also increased, and amino acids such as blood methionine (methionine) can also be increased.

2. Children with Hartnup disease have increased urinary amino acids, and urinary proline, hydroxyproline and arginine are normal.

3. EEG examination.

4. Genetic testing and prenatal diagnosis.

5. X-ray, CT and MRI examinations.

Diagnosis and identification of amino acid metabolic diseases

diagnosis

It is mainly based on the typical clinical manifestations of different types of amino acid metabolic diseases, as well as laboratory tests to make a diagnosis. Genetic testing has the significance of diagnosis and differentiation.

Differential diagnosis

It needs to be differentiated from other causes such as lipid deposition disease, perinatal disease, nervous system damage, etc., mental retardation, seizures, tremors, ataxia, hyperreflexia and liver disease, dermatitis.

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