Urine qualitative measurement of organic acids was positive for increased level of homogentisic acid
. His urine sample turned brown following alkalinization (Figure 1)Thoracic spine radiograph showed calcification of the intervertebral disc spaces at all levels of the thoracic vertebrae with disc space narrowing and anterior and posterior osteophytes (Figure 3a, b), whereas lumbar spine radiograph revealed diffuse severe osteopenia with interbody disc space calcification in the umbar region (Figure 3c).
All 5 adult cases referred with strong suspicion of alkaptonuria, from medical OPD (n=1), orthopedic department (n=1) and dermatology departments (n=3) tested strongly positive for marked elevations of homogentisic acid
. Reason for this excellent diagnostic yield (100%) in adults could be due to ease of control of preanalytical factors like diet and early morning (first voided) sampling, in the setting of rational test referral owing to prominent clinical features like joint deformities and/or characteristic skin lesions.
Gallic acid, pyrogallol, protocatechuic acid, chlorogenic acid, p-hydroxybenzoic acid, caffeic acid, mangiferin, epicatechin, p-coumaric acid, ferulic acid, ECG, CG, ellagic acid, rutin, quercetin, kaempferol, homogentisic acid
, tannic acid, and vanillic acid were used as standards for HPLC analyses.
 Nonstandard abbreviations: HGD, homogentisate1,2-dioxygenase; HGA; homogentisic acid
; NTBC, 2-[2-nitro-4-trifluoromethylbenzoyl]-cyclohexane-1,3-dione.
Ochronosis is a syndrome that is characterized by pigmentation of various connective tissues, including human cartilage, and is caused by high concentrations of homogentisic acid
due to alkaptonuria (inherent homogentisic acid
oxidase deficiency) [1, 2].
AKU is caused by the deficiency of the homogentisate 1,2-dioxygenase enzyme which results in excretion of large quantities of homogentisic acid
(HGA) in the urine and a slowly progressive deposition of HGA and its oxidative product in cartilage, intervertebral disk and other connective tissues, leading to ochronotic arthropathy.