Williams syndrome is a rare, congenital (present at birth) disorder characterized by physical and developmental problems including an impulsive and outgoing (excessively social) personality, limited spatial skills and motor control, and intellectual disability (i.e., developmental delay, learning disabilities, mental retardation, or attention deficit disorder). Other features include characteristic "elfin-like" facial features, heart and blood vessel problems, hypercalcemia (elevated blood calcium levels), low birth weight, slow weight gain, feeding problems, irritability during infancy, dental and kidney abnormalities, hyperacusis (sensitive hearing), and musculoskeletal problems. Symptoms vary among patients. Although individuals with Williams syndrome may show competence in areas such as language, music, and interpersonal relations, their IQs are usually below average, and they are considered moderately to mildly retarded. Scientists have learned that most individuals with Williams syndrome have a deletion of genetic material on chromosome 7. This probably causes the physical and developmental problems experienced by patients.