| Chromosomal Pattern | Physical Appearance | Psychological Characteristics | Incidence* |
|---|---|---|---|
| XXY (Klinefelter Syndrome) | Males. Usual male characteristics at puberty do not develop—penis does not grow, voice does not deepen. Usually sterile. Breasts may develop. | Can have some learning disabilities, especially in language skills. | 1 in 700 males |
| XYY (Jacob’s Syndrome) | Males. Typically tall. | Risk of intellectual impairment, especially in language skills. | 1 in 1,000 males |
| XXX (Triple X Syndrome) | Females. Normal Appearance. | Impaired in most intellectual skills. | 1 in 500 females |
| XO (only one sex chromosome) (Turner Syndrome) | Females. Short, often “webbed” neck. Secondary sex characteristics (breasts, menstruation) do not develop. | Some learning disabilities, especially related to math and spatial understanding; difficulty recognizing facial expressions of emotion. | 1 in 2,000 females |
| *Incidence is approximate at birth. Source: Hamerton & Evans, 2005; Aksglaede et al., 2013; Powell, 2013; Stocholm et al., 2013 | |||