ɪn tˈuː θˈaʊzənd nˈaɪn, sˈaɪəntɪsts dɪskˈʌvɚd ðæt ɐn ɪnhˈɛɹɪɾᵻd dʒˈiːn dˌuːplɪkˈeɪʃən ɪz ɹᵻspˈɑːnsᵻbəl fɚðə fæmˈɪlɪəl fˈɔːɹm ʌv ðɪs dɪsˈoːɹdɚ.
In 2009, scientists discovered that an inherited gene duplication is responsible for the familial form of this disorder.