Erratum

Following publication of the original article [1] it was brought to our attention that an affiliation was missing from the article. Please note that Margarita Romeo should have three affiliations: 1, 2 and 7. The additional affiliation which was missing from the original article is as follows:

7Departament de Medicina, Universitat Autónoma de Barcelona, Plaza Cívica, s/n, 08193 Bellaterra, Barcelona, Spain.