Alopecia areata and down syndrome: a true association or a coincidence.

Sir,

The cause of alopecia areata (AA) is not entirely understood, although a strong genetic basis for this condition has been suggested.[1] Several studies have showed that AA is associated with Down syndrome (DS), implicating that a causative gene for this condition is located on chromosome 21.[2] However, the number of studies that evaluated the link between these two conditions is small, and some studies failed to show a significantly high prevalence of AA in DS patients.[3] None of these surveys has checked the familial incidence of AA in these cases. Since an increased familial incidence of AA in DS patients with AA would suggest that the association with chromosome 21 is coincidental, we evaluated patients with DS from our AA clinic during the years 2011-12.

Patients were thoroughly examined and parents of patients were interviewed with emphasis on clinical course, severity of AA, familial history and associated conditions. During the time of the study, we found 14 DS patients with AA condition (mean age of onset 6.8). Total of 79% had patch-type AA [Figure 1], one had alopecia totalis (AT) and two had alopecia universalis (AU). Six patients had thyroid abnormalities and one patient had celiac disease. AA was reported in first- or second-degree relatives of eight patients (57%), as diagnosed by the study group or local dermatologists. Clinical data are summarized in Table 1.

Figure 1

A 9-year-old female with Down syndrome and a patch-type alopecia areata

Table 1

Summary of clinical characteristics of DS patients with AA

The fact that the DS patients we evaluated had such a high-rate of positive family history suggests that the association between the two disorders might have been coincidental. None of the previous association studies has inquired regarding possible family history of AA in affected DS patients. Additionally, since DS patients often suffer from a number of accompanying diseases, they are more often subject to physical examination by medical personnel. Therefore, it is possible that many of the AA lesions, which will go unnoticed in the general population, are being reported in DS patients, representing a selection bias.

In our patients, the mean age of onset was 6.8, which is lower than the average age in the general population.[1] Indeed, these numbers are consistent with the younger age of onset in DS patients. Additionally, scalp involvement was greater than in the general population, consistent with the more severe phenotype, which has often been attributed to DS, considering that in the general population only 5% of AA patients are expected to progress to AT or AU.[4] However, it should be noted that younger patients tend to progress to AT or AU more frequently;[5] therefore, this involvement could be attributed to the younger age of our patients.

DS patients are under stringent medical surveillance and under these conditions, skin diseases, such as AA, are more often diagnosed. This may have resulted in a selection bias in previous reports linking DS to AA. Our study is the first to investigate familial incidence of AA in DS patients, and the fact that many patients had a positive family history of AA suggests that the association to chromosome 21 is coincidental.