Histidinemia is a rare hereditary metabolic disorder characterised by the body's inability to produce histidase, a crucial enzyme essential for metabolising the amino acid histidine. This deficiency results in an elevated concentration of histidine in the blood, which marks individuals with this condition.

Signs & Symptoms:

Contrary to previous beliefs associating histidinemia with intellectual disability and speech disorders, current research suggests these conditions may be coincidental. While many patients show no symptoms and remain asymptomatic, some individuals with the disorder report clinical manifestations.

The mismatch with harmless newborn screening results suggests that the disorder might raise the chance of developing central nervous system (CNS) problems. These issues may happen mainly in unfavourable situations, like abnormal perinatal events.

Causes:

Histidinemia follows an autosomal recessive inheritance pattern, where the child inherits recessive genes from both parents. The risk of a child being born with histidinemia is one in four for each pregnancy, irrespective of gender. Researchers attribute histidinemia to mutations in the human histidase (HAL) gene.

Affected Populations:

As one of the most common inborn metabolic errors, histidinemia is estimated to occur in approximately one in 11,500 births. Data suggest a higher prevalence among individuals of French, Canadian, or Japanese descent.

The screening of newborns shows that approximately one in 8,600 infants in Quebec, Canada, and one in 9,500 infants in Japan have the disorder. However, it is important to note that this condition does not immediately threaten their lives.

Diagnosis:

Routine screening of newborns for histidinemia involves blood or urine tests, with a diagnosis based on elevated levels of histidine in the samples.

Treatment:

Histidinemia is generally considered a benign, asymptomatic disorder that does not necessitate specific treatment. Genetic counselling may be beneficial for affected individuals and their families. Treatment primarily focuses on providing symptomatic relief and supportive care for any coincidental problems that may arise.

In shedding light on histidinemia, medical professionals strive to deepen our understanding of this condition, emphasising the importance of early diagnosis and appropriate support for affected individuals and their families.