Familial Sarcoidosis Prevalent in Certain Populations Worldwide, Review Suggests

A literature review of research performed in specific populations from countries worldwide estimated a heritability of 60 to 70 percent for familial sarcoidosis, a study has found.

The study titled “Clinical epidemiology of familial sarcoidosis: A systematic literature review” was published in the journal Respiratory Medicine.

While the underlying cause of sarcoidosis remains unknown, environmental cues — including an allergic reaction, an infection, or exposure to chemicals — are likely triggers. A genetic component is also possible, especially since sarcoidosis can run in families.

A team of researchers in The Netherlands sought to identify the epidemiologic features associated with cases of familial sarcoidosis. They conducted a systematic review of studies reporting familial cases of sarcoidosis — defined as the presence or history of sarcoidosis in one or more family members of a sarcoidosis patient.

In total, the team analyzed 27 studies published between 1947 and 2017. Familial cases of sarcoidosis were reported in nine countries, seven of which were in Europe.

The pooled prevalence of familial sarcoidosis in all the studies analyzed was 9.5%. The prevalence of familial sarcoidosis, according to 12 studies, was the highest in French (44.7%), African American (35.0%), Dutch (16.5%), and Irish (9.6%) patients.

In two studies, the estimated heritability rate in an African-American population and in a Danish/Finish population was above 60 percent. The researchers believe that these high rates found in such different populations indicate that there is a determinant and common factor behind familial sarcoidosis. However, despite this high heritability, the genetic causes of familial sarcoidosis have not been identified yet.

Furthermore, the team argues that not all familial cases can be explained directly by genetics, and that environmental factors also play a role. For instance, occupational exposures associated with sarcoidosis development include exposure of over one year to titanium, vegetable dust, high indoor humidity levels, water damage, and musty odors.

Different environments could explain the heterogeneity of familial sarcoidosis, and is estimated that these factors influence 34 percent of the disease cases, according to the team.

Researchers saw that familial sarcoidosis occurs more often in siblings compared with parent-child relationships, and more often in mother-child compared with father-child relationships.

The team concluded that the “prevalence of familial sarcoidosis is high in specific study populations from countries worldwide,” and the estimated heritability of 60-70% “suggests a shared determinant, and the heterogeneous familial risk, associated with both genetic and environmental factors.”

The researchers also noted that “familial relative risks and clinical phenotypes may differ between ethnic groups and relative types,” but that further studies are needed. Such “findings are potentially important in patient care and deserve investigation in the future,” they wrote.