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Prevalence of autism in early 1970s may have been underestimated

BMJ 2001; 323 doi: (Published 15 September 2001) Cite this as: BMJ 2001;323:633

Prevalence of autism in the past may have been underestimated

Autistic Spectrum Disorders (ASDs) cover a range of disorders
characterized by impairments in social interactions, pattern of
communication and restricted, repetitive behaviours. We have previously
demonstrated a 4-fold rise in the incidence of diagnosed ASDs in pre-
school children from 1991&1992 to 1995&1996 in the West
Midlands(1). Heussler et al(2)have reported reviewed data from the 1970s
suggesting that by contempory standards the prevelance of ASDs in the
1970s was probably as high as it now appears.

We undertook a time trend analysis of the West Midlands data set to
see if the observed increase in incidence was compatible with a new
biological aetiology or with improved diagnosis of essentially the same

Clinical data on the 148 children ascertained in the original study
(1) was collected from the medical notes in a systematic way using a
proforma. Complete data was available for analysis on 134. Data in the
following domains were recorded: family history of ASD, developmental,
neurological, other medical and psychiatric disorder; obstetric and past
medical history; personal history of epilepsy and other neurological and
medical disorder, learning difficulties and other developmental problems;
abnormalities on physical examination including visual and hearing
deficits. Linear by linear association tests were used to test for time-
trends in the data.

There were no significant trends found between any of the
characteristics examined.

To conclude there was no evidence for a change in the prevalence of
associated clinical features in children with ASD over time. We failed to
find an indication that the apparent rise in incidence was due to the
emergence of a single new cause of autism. This result is consistent,
however, with improved identification and diagnosis of ASDs in the
population over time.

William Whitehouse, Senior Lecturer in Paediatric Neurology,
University of Nottingham

Mark Abbas, Medical Student, University of Birmingham

Judy Powell, Lecturer in Public Health & Epidemiology, University
of Birmingham

1. Powell et al. Changes in the incidence of childhood autism and
other autistic spectrum disorders in preschool children from two areas of
the West Midlands, UK. Developmental Medicine & Child Neurology

2. Heussler et al. Prevalence of autism in early 1970s may have been
underestimated. British Medical Journal 2001:323:633.

Competing interests: No competing interests

29 September 2001
William Whitehouse
Senior Lecturer in Paediatric Neurology
University of Nottingham