title: A letter to the editor on the article by Burri et al.
authors.affiliation: School of Sexology, University of L'Aquila, Rome, Italy; Centre d'échographie, Saint Germain en Laye, France; Hôpital de Saint Germain en Laye, Saint Germain en Laye, France; Department of Twin Research and Genetic Epidemiology, King's College London, London, UK.
authors.forename: Emmanuele A
authors.initials: EA
authors.lastname: Jannini
authors.affiliation: School of Sexology, University of L'Aquila, Rome, Italy; Centre d'échographie, Saint Germain en Laye, France; Hôpital de Saint Germain en Laye, Saint Germain en Laye, France; Department of Twin Research and Genetic Epidemiology, King's College London, London, UK.
authors.forename: Giovanni Luca
authors.initials: GL
authors.lastname: Gravina
authors.affiliation: School of Sexology, University of L'Aquila, Rome, Italy; Centre d'échographie, Saint Germain en Laye, France; Hôpital de Saint Germain en Laye, Saint Germain en Laye, France; Department of Twin Research and Genetic Epidemiology, King's College London, London, UK.
authors.forename: Odile
authors.initials: O
authors.lastname: Buisson
authors.affiliation: School of Sexology, University of L'Aquila, Rome, Italy; Centre d'échographie, Saint Germain en Laye, France; Hôpital de Saint Germain en Laye, Saint Germain en Laye, France; Department of Twin Research and Genetic Epidemiology, King's College London, London, UK.
authors.forename: Pierre
authors.initials: P
authors.lastname: Foldès
authors.affiliation: School of Sexology, University of L'Aquila, Rome, Italy; Centre d'échographie, Saint Germain en Laye, France; Hôpital de Saint Germain en Laye, Saint Germain en Laye, France; Department of Twin Research and Genetic Epidemiology, King's College London, London, UK.
authors.forename: Andrea Virginia
authors.initials: AV
authors.lastname: Burri
authors.affiliation: School of Sexology, University of L'Aquila, Rome, Italy; Centre d'échographie, Saint Germain en Laye, France; Hôpital de Saint Germain en Laye, Saint Germain en Laye, France; Department of Twin Research and Genetic Epidemiology, King's College London, London, UK.
authors.forename: Lynn
authors.initials: L
authors.lastname: Cherkas
authors.affiliation: School of Sexology, University of L'Aquila, Rome, Italy; Centre d'échographie, Saint Germain en Laye, France; Hôpital de Saint Germain en Laye, Saint Germain en Laye, France; Department of Twin Research and Genetic Epidemiology, King's College London, London, UK.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Spector