The causes of developmental disabilities are varied and remain unknown in a large proportion of cases. Even in cases of known etiology, the line between "cause" and "effect" is not always clear, leading to difficulty in categorizing causes. Genetic factors have long been implicated in causing developmental disabilities. These conditions are also believed to have a large environmental component, and the relative contributions of nature versus nurture have been debated for decades. Preterm birth is known to be a predictor for potential developmental disabilities later in childhood, which complicates the question of nature versus nurture, as Current theories on causation focus on genetic factors; more than 1,000 known genetic conditions include developmental disabilities as a symptom. Developmental disabilities affect between 1 and 2% of the population in most western countries, although many government sources acknowledge that statistics are flawed in this area. The worldwide proportion of people with developmental disabilities is believed to be approximately 1.4%. Such disabilities are twice as common in males as in females, and some researchers have found that the prevalence of mild developmental disabilities is likely to be higher in areas of poverty and deprivation, and among people of certain ethnicities.
symptom of Prader–Willi syndrome
symptom of Scheuermann's disease
symptom of Rotor syndrome
symptom of Klinefelter syndrome
symptom of Klippel–Feil syndrome
symptom of Kallmann syndrome
symptom of Laron syndrome
symptom of Angelman syndrome