Brief Report: Monosodium Urate Monohydrate Crystal Deposits Are Common in Asymptomatic Sons of Patients With Gout: The Sons of Gout Study

Abstract

Objective: To estimate the prevalence and distribution of asymptomatic monosodium urate monohydrate (MSU) crystal deposition in sons of patients with gout.

Methods: Patients with gout were mailed an explanatory letter with an enclosed postage-paid study packet to mail to their son(s) age ≥20 years old. Sons interested in participating returned a reply form and underwent telephone screening. Subsequently, they attended a study visit at which blood and urine samples were obtained and musculoskeletal ultrasonography was performed, with the sonographer blinded with regard to the subject's serum urate level. Images were assessed for double contour sign, intraarticular or intratendinous aggregates/tophi, effusion, and power Doppler signal. Logistic regression was used to examine associations. Adjusted odds ratios (OR_adj ) and 95% confidence intervals (95% CIs) were calculated.

Results: One hundred thirty-one sons (mean age 43.8 years, mean body mass index 27.1 kg/m² ) completed assessments. The serum urate level was ≥6 mg/dl in 64.1%, and 29.8% had either a double contour sign or intraarticular aggregates/tophi in ≥1 joint. All participants with MSU deposition had involvement of 1 or both first metatarsophalangeal joints. Intratendinous aggregates were present in 21.4% and were associated with intraarticular MSU crystal deposits (OR_adj 2.96 [95% CI 1.17-7.49]). No participant with a serum urate level of ≤5 mg/dl had MSU crystal deposition seen on ultrasonography, and 24.2% of those with serum urate levels between 5 and 6 mg/dl had ultrasonographic MSU deposition. MSU crystal deposition was associated with increasing serum urate levels (OR_adj 1.61 [95% CI 1.10-2.36] for each increase of 1 mg/dl).

Conclusion: Asymptomatic sons of patients with gout frequently have hyperuricemia and MSU crystal deposits. In this study MSU crystal deposits were present in participants with serum urate levels of ≥5 mg/dl. Evaluation of subjects without a family history of gout is needed to determine whether the threshold for MSU crystal deposition is also lower in the general population.