Histidinemia. Classical and atypical form in siblings

Area of Science:

• Biochemistry
• Genetics
• Pediatrics

Background:

• Histidinemia is an inborn error of histidine metabolism.
• Clinical and biochemical heterogeneity exists in histidinemia.
• Genetic basis of histidinemia involves mutations in the *HPD* gene.

Purpose of the Study:

• To describe clinical and biochemical findings in two brothers with histidinemia.
• To differentiate between classical and atypical forms of histidinemia.
• To investigate family inheritance patterns.

Main Methods:

• Clinical assessment of affected individuals.
• Biochemical analysis of blood histidine levels.
• Enzyme activity assays for histidase (skin).

Main Results:

• The younger brother (6 years) presented with classical histidinemia.
• The older brother (13 years) exhibited an atypical form with partial skin histidase deficiency and prolonged blood histidine half-life.
• The mother was identified as a heterozygous carrier; the father and sister appeared unaffected.

Conclusions:

• Histidinemia can manifest with distinct clinical and biochemical phenotypes within a single family.
• Partial enzyme deficiency and altered histidine metabolism characterize atypical histidinemia.
• Genetic counseling and carrier screening are important for families with histidinemia.