chemistry

Histidinemia

Histidinemia is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Histidinemia rather than just read about it. In short: Histidinemia is a rare autosomal recessive metabolic disorder caused by a deficiency of the enzyme histidase. Histidase is needed for the metabolism of the amino acid histidine.

Key takeaways

Histidinemia belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Histidinemia to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Histidinemia from memory before moving on to harder problems.

Reference excerpt

Histidinemia is a rare autosomal recessive metabolic disorder caused by a deficiency of the enzyme histidase. Histidase is needed for the metabolism of the amino acid histidine. Although originally thought to be linked to multiple developmental disorders histidinemia is now accepted as a relatively benign disorder, leading to a reduction in the prevalence of neonatal screening procedures.

Presentation Histidinemia is considered benign as most patients remain asymptomatic, early correlational evidence from the first decade of histidinemia research lead to the theory that histidinemia was associated with multiple developmental symptoms including hyperactivity, speech impediment, developmental delay, learning difficulties, and sometimes intellectual disability. However, these claims were later deemed coincidental as a large subpopulation of infants that tested positive for histidinemia were found to have normal IQ and speech characteristics; as such histidinemia has since been reclassified as a benign inborn error of metabolism.

Molecular mechanism

Histidinemia occurs as the result of an inborn error of metabolism that may result in either an inactive or a severely reduced histidine ammonia-lyase (HAL) enzyme activity. The gene that encodes for HAL spans a roughly 25 kb and consists of 21 exons located at the 12q22-q24.1 position of human chromosome 12. There are eight mutations currently associated with autosomal recessive histidinemia, that include: four missense mutations, two exonic polymorphisms and two intronic polymorphisms.

Diagnosis Histidenemia is characterized by increased levels of histidine, histamine and imidazole in blood, urine and cerebrospinal fluid. This also results in decreased levels of the metabolite urocanic acid in blood, urine, and skin cells. In Japan, neonatal screening was previously performed on infants within one month of birth; infants demonstrating a blood histidine level of 6 mg/dl or more underwent careful testing as suspected histidinemia cases. A typical characteristic of histidinemia is an increase in the blood histidine levels from normal levels (70–120 μM) to an elevated level (290–1420 μM). Further testing includes: observing histidine as well as imidazolepyruvic acid metabolites in the urine. However, neonatal urine testing has been discontinued in most places, with the exception of Quebec.

Treatment It has been suggested that a possible method of treatment for histidinemia is through the adoption of a diet that is low in histidine intake. However, the requirement for such dietary restrictions is typically unnecessary for 99% of all cases of histidinemia.

Prevalence Histidinemia is a rare autosomal recessive disorder. However, histidinemia is considered the most prevalent inborn error of metabolism with a reported incidence of 1:8600 (Quebec); 1:180,000 (New York) and 1:9600 (Japan); and an average of 1:12,000 observed in the neonatal screening of over 20 million newborns.

See also Prolinemia Sarcosinemia Tyrosinemia

References

External links

Illustrations

Worked examples

Example 1 — a first encounter with Histidinemia

Start with the simplest possible case. Write down what Histidinemia claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Histidinemia before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Histidinemia ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Histidinemia

In research: Histidinemia appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Histidinemia in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Histidinemia is common in secondary-school and first-year university syllabi. It links to neighbouring topics Amino acid metabolism disorders, Autosomal recessive disorders, Rare diseases, so understanding it makes those chapters shorter.
In everyday life: Look for Histidinemia outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Histidinemia” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Histidinemia in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Histidinemia means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Histidinemia out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Histidinemia in simple terms?

Histidinemia is a rare autosomal recessive metabolic disorder caused by a deficiency of the enzyme histidase. Histidase is needed for the metabolism of the amino acid histidine.

Why does Histidinemia matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Histidinemia?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Histidinemia.