Evaluating the aortic stenosis phenotype before and after the effect of homogentisic acid lowering therapy: Analysis of a large cohort of eighty-one alkaptonuria patients

Abstract

Aims: A large alkaptonuria (AKU) cohort was studied to better characterise the poorly understood phenotype of aortic stenosis of rare disease AKU.

Methods and results: Eighty-one patients attended the National Alkaptonuria Centre (NAC) between 2007 and 2020. Nine only attended once. Fifty-one attended more than once and received nitisinone 2 mg daily. Twenty-one attended at least twice without receiving nitisinone. Assessments included questionnaire analysis, standard transthoracic echocardiography, as well as photographs of ochronotic pigment in eyes and ears at baseline when 2 mg nitisinone was commenced, and yearly thereafter. Blood and urine samples were collected for chemical measurement. The prevalence of aortic stenosis and aortic valve replacement were 22.2 and 6.2% in the current group. Aortic maximum velocity (Vmax) was directly related to varying degrees to age (R = 0.58, p < 0.001), systolic blood pressure (R = 0.32, p < 0.05), serum homogentisic acid (sHGA) (R = 0.28, p < 0.05), ochronosis scores (R = 0.72, p < 0.001), and alkaptonuria severity score index (AKUSSI) (R = 0.58, p < 0.001) on linear regression analysis. Age and ochronosis scores were significantly related to Vmax on multiple regression analysis (p < 0.005). Nitisinone decreased sHGA, 24-h urine HGA (uHGA₂₄₎, ochronosis scores and AKUSSI significantly at all visits post-nitisinone. Nitisinone decreased Vmax change scores at final visit comparison, with a similar pattern at earlier visits.

Conclusion: Aortic valve disease is highly prevalent in this NAC cohort, and strongly associated with ochronosis and disease severity. Nitisinone decreases ochronosis and had a similar significant effect on Vmax.

Keywords: Alkaptonuria; Aortic stenosis; Aortic valve replacement; Homogentisic acid; Nitisinone; Ochronosis.