Men with Klinefelter syndrome had markedly higher odds of autoimmune disease

Design

Systematic review and meta-analysis of observational studies

Population

2,289 men with Klinefelter syndrome and 51,250,114 controls

Primary outcome

Autoimmune disease or autoantibody positivity

Effect

Overall OR 23.25 (9.96–54.31); clinical disease OR 48.46 (17.68–132.87)

This meta-analysis combined six studies (eight datasets) of 2,289 men with Klinefelter syndrome (47,XXY) and more than 51 million controls.

Klinefelter syndrome was associated with much higher odds of autoimmunity overall (OR 23.3, 95% CI 10.0 to 54.3; I² 66%), and especially of clinically manifest autoimmune disease (OR 48.5, 17.7 to 132.9) rather than autoantibodies alone (OR 10.0, 1.2 to 84.8). The diseases involved were largely those that predominate in women and are linked to interferon: lupus, Sjögren's syndrome, systemic sclerosis, autoimmune thyroid disease and type 1 diabetes.

The estimates are imprecise and the studies few, but the direction fits the idea that a second X chromosome raises autoimmune risk. Klinefelter syndrome is common and frequently undiagnosed, so the practical step runs in both directions: think of autoimmunity in men with known Klinefelter, and think of Klinefelter in a man presenting with lupus.

• Consider autoimmune disease early in men with Klinefelter syndrome who present with rash, arthralgia, sicca or Raynaud's.
• In a man with lupus or Sjögren's, look for features of Klinefelter — small testes, gynaecomastia, tall stature, infertility.
• Consider karyotype testing when those features are present.
• Remember that testosterone treatment does not remove the extra X chromosome.

Why it matters

It links two conditions that are each often missed, and gives a reason to look for one when the other is found.

Don't overread it

Few, heterogeneous observational studies — the size of the increase is highly uncertain.

The statistics, in plain English

Odds ratios of 23 to 48 are very large, but the intervals are extremely wide (17 to 133 for clinical disease). That reflects few studies and few cases. The direction is consistent; the exact size is not reliable.

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