A Burglar Mystery

A home invader was masked, gloved and meticulous enough to vacuum and scrub the victim’s apartment so as not to leave any hair or skin cells for forensic analysis. The vacuum bag was not left behind. He had used the toilet to urinate but brushed the bowl for five minutes. And he subsequently flushed two or three more times.
There is usually no DNA present in urine, but it was possible that the burglar was unaware of the fact. And few men realize how much splashing urinating actually causes when one urinates while standing. The side of the counter next to the bowl was stained with a few black spots. Laboratory analysis revealed that the spots were not mold but contained urea and dark brown products derived fromhomogentisic acid.”Well, something is definitely known about the crook”, said the forensic expert at the lab.

What had they stumbled upon?

The burglar suffered from a metabolic disorder known as alcaptonuria. (The scenario is fictional.)

In people without the condition, an enzyme converts a derivative(homogentisic acid) of the amino acids phenylalanine or tyrosine into maleyl acetoacetate, which eventually is broken down into colorless ions.
But in people who suffer from the condition, homogentisic acid accumulates and is excreted in the urine. On standing for a couple of hours, homogentisic acid is eventually oxidized and turns into a dark melanin-like substance. The long-term effects of the disorder include spinal and joint damage.

Archibald Garrod, the physician who also shed light on gout, realized that the condition was not due to bacteria but to some metabolic disorder. Known as black diaper syndrome, it was observed in newborns who lack bacterial colonies. Garrod also noticed that alcaptonuria is rare in the general population (1 in 100 000 to 1 in 250 000) but more common in Dominicans, Slovakians and among children of first cousins. In 1995, Spanish scientists found a gene in fungus that codes for homogentisate dioxygenase. In patients with alcaptonuria a single gene has one of a few possible mutations that lead to the production of the dysfunctional enzyme. It is one of those molecular diseases where two copies of a defective gene must be carried for the disease to manifest itself.




Alcaptonuria diagnosed in a 4-month-old baby girl: a case report. Cases Journal 2008, 1:308

Natural History of Alcaptonuria N Engl J Med 2002; 347:2111-2121 December 26, 2002

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