The success of dietary protein restriction in alkaptonuria patients is age-dependent

Alkaptonuria is characterized by an increased urinary excretion of homogent isic acid, pigmentation of cartilage and connective tissues, and ultimately the development of inflammatory arthropathy. Various diets low in protein have been designed to decrease homogentisic acid excretion and to prevent t he ochronotic pigmentation and arthritic lesions. However, limited informat ion is available on the long-term beneficial effects of these diets. We rev iewed the medical records of 16 patients aged 3-27 years (4 > 18 years) to ascertain the age of diagnosis, growth, development, social behaviour, sign s of complications and longitudinal dietary compliance. The diagnosis of al kaptonuria was made at an average age of 1.4 years (2 months-4 years); foll owing the diagnosis all patients were prescribed a diet with a protein cont ent of 1.5 g/kg per day. All patients showed normal growth and development, and no major complications of the disease. Behavioural problems associated with poor dietary compliance emerged as the main problem. Dietary complian ce decreased progressively with age. The effect of dietary protein restrict ion in homogentisic acid excretion was studied by fixing the amounts of pro tein in the diet at 1 g/kg per day and 3.5-5 g/kg per day during 8 days. Tw elve patients, aged 4-27 years, participated in the investigation. Protein restriction resulted in a significantly lower excretion of homogentisic aci d in the urine of children younger than 12 years (p < 0.01), whereas this e ffect was less obvious for adolescent and adult patients. The results sugge st that restriction of protein intake may have a beneficial effect on alkap tonuric children; but continuation of this regimen to older age seems quest ionable and not practical.