Babies can sometimes be born with atypical reproductive organs or external genitalia – these conditions are called Differences/Disorders of Sex Development (DSD). In some cases, if the genetic cause is unknown, doctors can be left guessing as to the best treatment. Changes in the Desert Hedgehog (DHH) gene can result in DSD, although this is rare, and it is not always clear if the genetic changes are the only cause. This study has used a cell culture system to assess whether novel DHH gene changes alter the function of this gene. This provided important evidence for or against these genetic changes being causative. It allowed more accurate genetic information for patients, and therefore more informed decisions for clinical care. Use of this method will be important in the future when new and uncharacterised DHH changes are found in DSD patients. (By Dr. Katie Ayers, https://jmg.bmj.com/content/early/2019/04/23/jmedgenet-2018-105893 )