Carnosinemia


Carnosinemia

Description, Causes and Risk Factors:

An autosomal recessive congenital disease, characterized by the presence of excess amounts of carnosine in the blood and urine and caused by a genetic deficiency of the enzyme carnosinase. Clinically characterized by progressive neurologic damage, severe mental retardation, and myoclonic seizures.

The gene for carnosinase is located on chromosome 18, an autosome. The carnosine dipeptidase-1 gene (CNDP1) controls tissue and serum carnosinase. Mutations in CNDP1 are responsible for carnosinase deficiency, resulting in carnosinemia.

Carnosinemia is inherited in an autosomal-recessive pattern and in one patient was linked to deletion in the long arm of chromosome 18 at the position q21.3. Only 24 cases have been reported Worldwide.

Carnosinemia

Carnosinemia is an autosomal recessive disorder, which means the defective gene is located on an autosome, and two copies of the defective gene - one from each parent - are required to inherit the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder.

Ten individuals with carnosinemia have been identified. All continued to excrete increased amounts of carnosine in their urine despite a meat-free diet for 3 days. Serum carnosinase activity ranged from 0-30% of normal. In four individuals a normal Km for carnosine of 0.12 mM was observed, while in five individuals an increased Km was found. Homocarnosine levels in CSF in three individuals ranged from 3.4 to 15 mM. Clinical symptoms in these individuals were as follows: attention deficit disorder: 4; non progressive developmental delay: 1; neurofibromatosis: 1; absences seizures: 1; severe, but non-progressive mental retardation, seizures and neurosensory hearing loss: 1; progressive childhood dementia: 1; clinically normal: 1. There was no correlation between severity and type of the neurological symptoms and residual serum carnosinase activity. Although a definite conclusion can only be made after a considerably higher number of individuals has been analyzed, the suspicion that serum carnosinase deficiency is unrelated to the neurological symptoms is strengthened by these observations. There may, however, be an association with a predisposition for mental deficiency.

Symptoms:

Several patents with this disorder have been asymptomatic. When symptoms are present, they vary widely and can include myoclonic and/or absence seizures, psychomotor retardation, spastic paraparesis, hypotonia, tremor, mental retardation, retinitis pigmentosa, peripheral sensory neuropathy, optic atrophy, neurosensory hearing loss, progressive childhood dementia, nonspecific electroencephalographic abnormalities, and attention deficit disorder. No correlation between the severity of neurologic abnormalities and residual carnosinase activity is known. No definite conclusion can be drawn about the relationship between serum carnosinase deficiency and the neurologic defects.

Diagnosis:

The diagnosis is confirmed by the presence of low carnosinase activity. Serum carnosinase is synthesized in the brain, where it is secreted into cerebrospinal fluid and then into the systemic circulation.

Carnosinase exists in two isoforms. Tissue carnosinase is found in the liver, kidney, and spleen, and serum carnosinase is found in serum (plasma), as well as in the brain and spinal fluid. These enzymes result from different gene products and differ not only in their distribution but also in their enzymatic properties. Specifically, although under appropriate conditions both isoforms catalyze the hydrolysis of the dipeptide carnosine (?-alanyl-L-histidine), only serum carnosinase is able to hydrolyze homocarnosine (?-aminobutyryl-L-histidine).

Treatment:

No efficient treatment is available. The first goal is to identify and treat any underlying problem such as diabetes. If no underlying problem exists, the primary treatment is dietary management, especially restriction of cholesterol intake, simple sugars, and refined carbohydrates that will elevate triglyceride levels. Omega-3 essential fatty acids (fish oils) have proved useful in reducing serum triglycerides. Drug therapy may also be used to lower the plasma triglyceride or cholesterol level when diet alone is ineffective. A carnosine/anserine-free diet has been used.

Growth hormone therapy is being investigated.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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