Except for a few very rare voices (such as the American male soprano Michael Maniaci or singers with a disorder such as Kallmann syndrome), singers called countertenors generally sing in the falsetto register, sometimes using their modal register for the lowest notes.
Down syndrome | Tourette syndrome | Asperger syndrome | Marfan syndrome | Down Syndrome | Turner syndrome | Down's syndrome | Asperger's syndrome | Williams syndrome | Stockholm syndrome | Severe acute respiratory syndrome | Rett syndrome | Irukandji syndrome | Chronic fatigue syndrome | Wiskott–Aldrich syndrome protein | Tourette Syndrome Association | syndrome | severe acute respiratory syndrome | Premenstrual syndrome | Le syndrome de Peter Pan | Alport syndrome | Usher syndrome | The China Syndrome | Sudden Infant Death Syndrome | Stockholm Syndrome (band) | Stockholm Syndrome | Stickler syndrome | Stevens–Johnson syndrome | Sjögren's syndrome | Restless legs syndrome |