dysphonia Adductor spasmodic dysphonia (ADSD) is the most common type, affecting around 87% of individuals with SD. In ADSD, sudden involuntary muscle movements or spasms cause the vocal folds (or vocal cords) to squeeze together and stiffen. As the name suggests, these spasms occur in the adductor muscles of the vocal folds, specifically the thyroarytenoid and the lateral cricoarytenoid. These spasms make it difficult for the vocal folds to vibrate and produce voice. Words are often cut off or are difficult to start because of the muscle spasms. Therefore, speech may be choppy but differs from stuttering. The voice of an individual with adductor spasmodic dysphonia is commonly described as strained or strangled and full of effort. Surprisingly, the spasms are usually absent while laughing, speaking at a high pitch, or speaking while singing, but singers can experience a loss of range or the inability to produce certain notes of a scale or with projection. Stress, however, often makes the muscle spasms more severe. Abductor spasmodic dysphonia Abductor spasmodic dysphonia (ABSD) is the second most common type, affecting around 13% of individuals with SD. In ABSD, sudden involuntary muscle movements or spasms cause the vocal folds to open. As the name suggests, these spasms occur in the single abductor muscle of the vocal folds, called the posterior cricoarytenoid. The vocal folds cannot vibrate when they are open. The open position of the vocal folds also allows air to escape from the lungs during speech. As a result, the voices of these individuals often sound weak, quiet, and breathy or whispery. As with adductor spasmodic dysphonia, the spasms are often absent during activities such as laughing or singing, but singers can experience a loss of range or the inability to produce certain notes of a scale or with projection. Mixed spasmodic dysphonia Mixed spasmodic dysphonia is the most rare type. Mixed spasmodic dysphonia involves both muscles that open the vocal folds and those that close them and therefore has features of both adductor and abductor spasmodic dysphonia. Some researchers believe that a subset of cases classified as mixed spasmodic dysphonia may actually be ADSD or ABSD subtype with the addition of compensatory voice behaviours that make it appear mixed. This further adds to the difficulty in achieving accurate diagnosis. Whispering dysphonia A fourth type has also been described. This appears to be caused by mutations in the TUBB4 gene on the