Purine and pyrimidine synthesis and metabolism disorders: Pathology review

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Purine and pyrimidine synthesis and metabolism disorders: Pathology review

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A 7-month-old boy is brought by his parents for a wellness visit. According to the mother, the patient has had poor weight gain despite getting adequate nutrition via a combination of breastmilk and solid foods. In addition, the patient has difficulty rolling from a prone to supine position or sitting upright unassisted. Vitals are within normal limits The patient is at the 5th percentile for weight. Physical examination reveals a frail and pale infant. Enzymatic testing is performed and confirms an absence of uridine monophosphate synthase activity. Which of the following findings is likely to be found on further evaluation?  


Three kids are brought to the clinic by three very concerned mothers.

The first one’s Carl, a 10 month old boy that, according to his mother, is always sick with bronchitis and diarrhea.

On physical examination, you notice that Carl is quite small for his age.

Laboratory studies are obtained, showing an absolute lymphocyte count of 2,000 cells per cubic millimeter.

A sputum culture reveals that Carl’s bronchitis is caused by a fungal infection by Pneumocystis jirovecii.

Next comes Mark, a 2 year old boy with aggressive and self-destructive behavior, such as constantly biting his lips, tongue, and fingers.

In addition, Mark doesn’t seem to be able to walk or speak a word.

His mother tells you that her younger brother, so Mark’s uncle, was diagnosed with a rare disease that caused mental retardation, and she’s worried Mark may have it too.

Upon physical exam, you notice some orange sand-like deposits in his diapers.

Laboratory studies show elevated levels of uric acid in his blood.

Finally, you see Laura, a 4 month old girl with a history of anemia that was diagnosed some days after birth.

Since then, Laura has been on a bottle-feeding regimen with folate and vitamin B12 supplementation; however, her anemia is not getting any better.

On examination, you notice cloudy urine that left some residues on Laura’s diaper, so you ask for a urinalysis.

Results revealed that the residues are orotic acid crystals.

Based on the initial presentation, all three cases seemed to be due to purine and pyrimidine metabolism disorder.

But first, a bit of biochemistry review.

Normally, each nucleotide can be broken down into a sugar that’s either a deoxyribose in DNA or a ribose in RNA, followed by one to three phosphate groups, and a nucleobase, which can be either a purine or a pyrimidine.

There are two purine bases, adenine and guanine; and three pyrimidine bases, cytosine, thymine, and uracil.

Now, the nucleoside based on adenine and ribose is adenosine, and a nucleotide based on adenosine and one phosphate would be adenosine monophosphate, or AMP for short; whereas the same combination with a deoxyribose would be deoxyadenosine monophosphate, or dAMP; and the same naming convention applies to all the other nucleobases.


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  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Mechanisms of Enzyme-Catalyzed Group Transfer Reactions" Annual Review of Biochemistry (1978)
  6. "Variable Expression of HPRT Deficiency in 5 Members of a Family With the Same Mutation" Archives of Neurology (2008)
  7. "Inborn errors of pyrimidine metabolism: clinical update and therapy" Journal of Inherited Metabolic Disease (2014)

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