Disorders of Histidine Metabolism

The primary disorders of histidine metabolism are histidinemia and uroca-nase deficiency (urocanic aciduria). 

Histidinemia is an autosomal recessive disorder that is benign in most affected individuals. The incidence from newborn screening is 1 10000, making histidinemia one of the most frequent of the inborn errors of metabolism. The enzyme defect is histidase, an enzyme normally expressed only in skin and liver. The block in conversion of histidine to urocanic acid results in an increased concentration of histidine in blood and urine and the abnormal presence of histidine metabolites in urine. 

Treatment with a histidine-restricted diet normalizes the biochemical phenotype but is not indicated for this probably harmless disorder although the treatment might be considered in any histidinemic infant who also has clinical abnormalities. 

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It is unlikely that the clinical signs and symptoms are associated with the disorders of histidine metabolism His, histidine. 

Fig. 5.2. Diagnostic flow chart for disorders of histidine metabolism...

Homocamosinosis. This disease is accompanied with pronounced increase of homocamosine level in brain and cerebrospinal liquid as well as camosine in urea with simultaneous disability to metabolize anserine into N -methyl-histidine (see [107]). Normal level of camosine and homocamosine is exceeded 20 and more times and this is accompanied with apparent neurological deficit. At the same time, relatives of the patients can get similar shifts in dipeptides metabolism with no neurological symptomatic. The cause of such disorder of metabolism in patients with homocamosinosis is that camosine splitting enzyme, carnosinase is mainly present in the inactive form [109,110],... 

Because of the high selectivity and sensitivity of the postcolumn fluorescence detection of histidine with OPA, the present HPLC method is applicable to a specific and rapid assay of histidine in human semm, blood, and urine after simple pretreatment. A recent paper demonstrated that the postcolumn detection with OPA was applicable to the simultaneous assays of histidine and its major metabolites cis- and frawi-urocanic acids) in human stratum corneum. " The postcolumn detection system was also applicable to the flow injection analysis (FIA) method for the assay of histidine in semm and urine. The FIA method enabled us to determine histidine in blood after pretreatment of the sample with A-ethylmaleimide (masking reagent of glutathione).These methods are useful in the diagnosis of histidinanemia, one of hereditary metabolic disorders characterized by a virtual deficiency of histidine ammonia-lyase. 

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