Hypertryptophanemia

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Hypertryptophanemia
Other namesFamilial hypertryptophanemia[1]
Tryptophan
SpecialtyEndocrinology Edit this on Wikidata

Hypertryptophanemia is a rare autosomal recessive[2] metabolic disorder that results in a massive buildup of the amino acid tryptophan in the blood, with associated symptoms and tryptophanuria (-uria denotes 'in the urine').[3][4]

Elevated levels of tryptophan are also seen in Hartnup disease,[5] a disorder of amino acid transport.[6] However, the increase of tryptophan in that disorder is negligible when compared to that of hypertryptophanemia.[1][5]

Symptoms and signs

A number of abnormalities and symptoms have been observed with hypertryptophanemia.[citation needed]

Musculoskeletal effects include:

adduction of the thumbs (where the thumb appears drawn into the palm, related to contracture of the adductor pollicis).[1][2]

Behavioral, developmental and other anomalies often include:

emotional lability (mood swings),[3] hyperaggressive behavior;[2] hypertelorism (widely-set eyes), optical strabismus (misalignment) and myopia.[1][2]

Metabolically, hypertryptophanemia results in tryptophanuria and exhibits significantly elevated serum levels of tryptophan, exceeding 650% of maximum (normal range: 25–73 micromole/l) in some instances.[2][3]

A product of the

congenital defect in the metabolic pathway where tryptophan is converted to kynurenine.[3]

Kynurenine, a metabolite of tryptophan

Genetics

Familial hypertryptophanemia has an autosomal recessive pattern of inheritance.

Hypertryptophanemia is believed to be inherited in an autosomal recessive manner.

carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder.[citation needed
]

Pathophysiology

At present, no specific enzyme deficiency nor genetic mutation has been implicated as the cause of hypertryptophanemia.[1][2] Several known factors regarding tryptophan metabolism and kynurenines, however, may explain the presence of behavioral abnormalities seen with the disorder.[citation needed]

Tryptophan is an

synthesis.[9] Aside from this crucial role, the remainder of tryptophan is primarily metabolized along the kynurenine pathway in most tissues, including those of the brain and central nervous system.[10][11][12][13]

As the main defect behind hypertryptophanemia is suspected to alter and disrupt the metabolic pathway from tryptophan to kynurenine,[2] a possible correlation between hypertryptophanemia and the known effects of kynurenines on neuronal function, physiology and behavior may be of interest.[14][15]

One of these kynurenines, aptly named

glutamate, respectively).[11][12] This action is in opposition to the agonist quinolinic acid, another kynurenine, noted for its potential as a neurotoxin.[10][13] Quinolinic acid activity has been associated with neurodegenerative disorders such as Huntington's disease, the neuroprective abilities of kynurenic acid forming a counterbalance against this process, and the related excitotoxicity and similar damaging effects on neurons.[13][14]

Indoleic acid excretion is another indicator of hypertryptophanemia.[2][3] Indirectly related to kynurenine metabolism, indole modifies neural function and human behavior by interacting with voltage-dependent sodium channels (integral membrane proteins that form ion channels, allowing vital synaptic action potentials).[15]

Diagnosis

Management

See also

References

  1. ^ a b c d e Online Mendelian Inheritance in Man (OMIM): 600627
  2. ^
    S2CID 27203561
    .
  3. ^
    PMID 6883719
    .
  4. PMID 7133092
    .
  5. ^ a b Online Mendelian Inheritance in Man (OMIM): 234500
  6. PMID 15286788
    .
  7. PMID 18486479
    .
  8. PMID 2186812
    .
  9. PMID 10867060
    .
  10. ^
    PMID 10936623
    .
  11. ^
    S2CID 21169913
    .
  12. ^
    S2CID 5823156
    .
  13. ^
    S2CID 30077788
    .
  14. ^
    S2CID 36859939
    .
  15. ^
    PMID 10443567
    .

External links
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