The majority of people with Down syndrome are referred to as standard trisomy 21. Despite their intellectual disabilities, people with Down syndrome have popularly been viewed as particularly loving and lovable people. Many different environmental conditions have been considered as possibly causing Down syndrome. Major exposure to radiation, for example from an atomic explosion, may actually result in fewer babies with Down syndrome, probably because of an increased miscarriage rate. Most people with Down syndrome enjoy reasonably good health, although heart, skin and sensory problems may be troublesome. People with Down syndrome appear to be less vulnerable to a number of psychiatric disorders - neuroses, schizophrenia, paranoia - than are individuals with other learning disabilities. Exploration of the indicators of Alzheimer's disease in people with Down syndrome has focused on three main areas: general ability (IQ); memory; and daily living skills such as dressing and toileting.