"It's the closest that a man will ever come to experiencing the pain of childbirth," the attending nurse proclaimed with a noticeable glee in her eyes. Her comment only added to my misery as I writhed in pain on a stretcher in the emergency room, waiting to pass a kidney stone.
Mineral deposits such as those that formed in my kidneys develop in one out of ten people during their lifetime and account for nearly ten out of every 1,000 hospital admissions.1 Stones can result whenever a chemical imbalance occurs in the kidney. The type of stone that forms depends upon the exact nature of the chemical imbalance and reflects different etiologies (causes). Calcium oxalate stones, the most common type, result from dehydration or excess levels of oxalate in the diet. (Oxalate is found in certain vegetables, nuts, berries, chocolate, and tea. 2) Sodium urate stones, a second type, are caused by an inborn error in metabolism that leads to excessive production of uric acid.3
Uric acid is the breakdown product of adenine and guanine (key components of DNA and RNA). As a normal metabolic activity, the cell turns over biomolecules-continually replacing "older" molecules with newly synthesized ones, thereby maintaining structural and functional integrity. The cell recycles most of the adenine and guanine generated from the breakdown of nucleotides (the building blocks of DNA and RNA) through what biochemists call the salvage pathways. Still, the cell targets a significant portion of adenine and guanine for breakdown and secretion in the form of uric acid.4
Uric acid possesses low solubility in blood serum, causing it to readily precipitate into the urinary tract if the body dehydrates or generates an excessive amount of the product (which can occur if the enzymes of the salvage pathway are defective).5
Except for primates, including human beings, all mammals further metabolize uric acid to a more soluble derivative. Evolutionary biologists suggest that the enzymes responsible for this transformation were lost in the evolutionary process that gave rise to primates (and humans).6 For these scientists, the elimination of adenine and guanine in the form of uric acid argues potently for evolution, since it appears to reflect poor design.7 Why would an all-powerful and all-knowing Creator put into place an imperfect biochemical process that leaves human beings so susceptible to kidney stones (and other disorders, like gout)? Evolutionists would maintain that the adenine and guanine elimination pathways represent nothing more than an evolutionary "kluge" job, an imperfection that barely gets the job done-not a Creator's perfect handiwork.
This perspective fails to consider, however, uric acid's full range of metabolic properties, some of which are beneficial. This compound is a potent antioxidant that scavenges the chemically corrosive hydroxyl free radical, singlet oxygen, and superoxide anion, all produced by the metabolic pathways that the cell uses to harvest chemical energy.8 The high levels of uric acid in the blood serum, though precariously poised to form stones in the urinary tract, also help prevent cancer and contribute to long human life spans. For other mammals, the conversion of uric acid to more soluble forms before elimination deprives them of a key antioxidant and limits their life spans.
When considered more broadly, it turns out that the primate adenine and guanine elimination pathways reflect an elegant, rather than a poor, design that finds an important use for a waste product. Though inborn metabolic error in the salvage pathway enzymes accounts for the less-common type of kidney stone, the more-common type is largely preventable by a balanced diet-which seems a small price to pay for cancer prevention and long life spans.
When the pain-killers finally took effect and I'd had a chance to research and reflect on what happened to me, I was able to muster thanks to God for kidney stones. But I don't think anyone will want me to share my story at the Thanksgiving dinner table this year.
- http://www.yourmedicalsource.com/library/kidneystones/KS_whatis.html, accessed March 11, 2003.
- http://www.urologychannel.com/kidneystones/index.shtml, accessed March 11, 2003.
- Lubert Stryer, Biochemistry, 3d ed. (New York: W. H. Freeman, 1988), 619-22.
- Stryer, 619-22.
- http://www.urologychannel.com/kidneystones/index/shtml, accessed March 11, 2003.
- Stryer, 619-22.
- Stephen Jay Gould, The Panda's Thumb: More Reflections in Natural History (New York: W. W. Norton, 1980), 19-26.
- Stryer, 619-22.