Assessment of Thyroid Function in Patients With Alkaptonuria
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Alkaptonuria is an autosomal recessive disorder caused by pathogenic variants in the HGD gene. Deficiency of the HGD enzyme leads to tissue deposition of homogentisic acid (HGA), causing severe osteoarthropathies and cardiac valve degeneration. Although HGD is vital for the catabolism of tyrosine, which provides the basis for thyroid hormone synthesis, the prevalence of thyroid dysfunction in alkaptonuria is unknown.

The objective of this study was to assess thyroid structure and function in patients with alkaptonuria. A single-center cohort study was conducted in a tertiary referral center including patients with alkaptonuria followed up for a median of 93 months between February 1, 2000, and December 31, 2018. The alkaptonuria diagnosis was based on clinical presentation and elevated urine HGA levels. A total of 130 patients were considered for participation. Prevalence of thyroid dysfunction in adults with alkaptonuria compared with the general population was assessed.

Results: Of the 130 patients, 5 were excluded owing to thyroidectomy as the cause of hypothyroidism. The study cohort consisted of 125 patients; the median age was 45 years. Most of the patients were men (72 [57.6%]). The prevalence of primary hyperthyroidism was 0.8%, similar to 0.5% observed in the general population. The prevalence of primary hypothyroidism was 16.0%, which is significantly higher than 3.7% reported in the general population. Women were more likely to have primary hypothyroidism than men. Patients with TPO antibodies had a higher likelihood of primary hypothyroidism than those without TPO antibodies. There was no significant difference in the prevalence of thyroid nodules or of cancer between patients in this study.

Conclusively, The high prevalence of primary hypothyroidism noted in patients with alkaptonuria in this study suggests that serial screening in this population should be considered and prioritized.