Purine Metabolism and Salvage Pathways to Genetic Code: Commaless and Universal

Purine salvage deficiencies

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This diagram illustrates the purine metabolism pathway, highlighting both de novo synthesis and salvage pathways, along with points where deficiencies can occur. Key enzymes like PRPP synthetase, HPRT, and APRT are shown, as well as the formation of uric acid for excretion.

ADA: adenosine deaminase, APRT: adenine phosphoribosyltransferase, HPRT: hypoxanthine guanine phosphoribosyltransferase, XO: xanthine oxidase, SCID: severe combined immune deficiency (autosomal recessive inheritance)

Adenosine deaminase deficiency

• ADA is required for degradation of adenosine and deoxyadenosine.
• ADA ↓ → ↑ dATP → ↓ ribonucleotide reductase activity → ↓ DNA precursors in cells → ↓ lymphocytes.
• One of the major causes of autosomal recessive SCID.

Lesch-Nyhan syndrome

Defective purine salvage due to absent HGPRT, which converts hypoxanthine to IMP and guanine to GMP. Compensatory ↑ in purine synthesis (↑ PRPP amidotransferase activity) → excess uric acid production. X-linked recessive.

Findings: intellectual disability, self-mutilation, aggression, hyperuricemia (red/orange “sand” [sodium urate crystals] in diaper), gout, dystonia, macrocytosis.

Treatment: allopurinol, febuxostat.

Genetic code features

Topics Covered:

• Purine Metabolism and Salvage Pathways
• Adenosine Deaminase (ADA) Deficiency
• Lesch-Nyhan Syndrome: Cause and Biochemistry
• Lesch-Nyhan Syndrome: Symptoms and Management
• Genetic Code: Unambiguous and Degenerate
• Genetic Code: Commaless and Universal