Prevalence of autism in Europe, North America and Oceania, 2000-2020: A systematic review

Background

Since the first study of the prevalence of autism spectrum disorder (ASD) in 1966, several studies from across the world have reported increasing prevalence of ASD in children. This has led to a debate whether childhood ASD cases are increasing in real time or the increase is essentially due to improved accessibility/referral to health services or changes in diagnostic criteria and accuracy.

Methods

MEDLINE and PSYCINFO databases were searched for studies of ASD prevalence estimates in Europe, North America and Oceania published during 2000-2020 (including prevalence data for 1993-2019). Data including age at diagnosis, gender, ethnicity, diagnostic criteria/tools, method(s) of case detection and prevalence per 10,000 population were extracted.

Results

75 studies, reporting a wide range of prevalence estimates, were included in the review. Overall, there was a steady and substantial increase in the prevalence of ASD in Europe, North America and Oceania during the last three decades. For Europe, the median prevalence was 59 per 10,000 population (range, 8 to 420; mean, 80). For North America, the median prevalence was 86 per 10,000 population (range, 11 to 247; mean, 95). For Oceania, the median prevalence was 47 per 10,000 population (range, 10 to 390; mean, 112). Overall, the prevalence was higher in White children compared to other ethnic groups.

Conclusions

It appears that several factors can be attributed to increasing prevalence of ASD in Europe, North America and Oceania. Some of the increase is likely due to increased case ascertainment, but other factors need further investigation to determine the reason(s) for increasing prevalence of ASD.

Key messages

There is a wide variation in the prevalence of ASD in populations of Europe, North America and Oceania. This is partly explained by differences in case ascertainment and sociodemographic factors. The differences in prevalence between ethnic groups need further investigation.

Constraints on cosmic strings from the LIGO-Virgo gravitational-wave detectors

Cosmic strings can give rise to a large variety of interesting astrophysical phenomena. Among them, powerful bursts of gravitational waves (GWs) produced by cusps are a promising observational signature. In this Letter we present a search for GWs from cosmic string cusps in data collected by the LIGO and Virgo gravitational wave detectors between 2005 and 2010, with over 625 days of live time. We find no evidence of GW signals from cosmic strings. From this result, we derive new constraints on cosmic string parameters, which complement and improve existing limits from previous searches for a stochastic background of GWs from cosmic microwave background measurements and pulsar timing data. In particular, if the size of loops is given by the gravitational backreaction scale, we place upper limits on the string tension Gμ below 10(-8) in some regions of the cosmic string parameter space.

Bidirectional axonal transport of free glycine in identified neurons R3--R14 of Aplysia

The axonal transport of 3H-amino acids was studied in the axons of identified neurons R3--R14 in the parietovisceral ganglion (PVG) of the mollusc Aplysia. The PVG was incubated (3--24 hr) in media containing physiological concentrations of single 3H-amino acids while the isolated nerve was superfused with plain or chemically altered media. The nerve was then sliced into sequential segments for biochemical analyses or fixed for autoradiography. 3H-glucine was transported at 70 mm/day in 6X greater quantities than other amino acids which were transported at less than 40 mm/day. In the 3H-glycine experiments, greater than 80% of the label transported into the nerve remained as free glycine, comigrating with glycine in thin-layer chromatographs. In autoradiographs of sections 4 mm from the ganglion-nerve barrier, greater than 50% of the silver grains were over R3--R14 axons which occupy less than 10% of the nerve cross-sectional area. EM autoradiographs confirmed that grains were within R3--R14 and not in surrounding glia. The selective transport of glycine was inhibited by Hg2+, by vinblastine and Nocodazole, and by low Ca2+ media. Autoradiographs of vinblastine-treated nerves showed a drastic reduction in label over R3--R14 and other axons. Label was also transported retrogradely; this transport rate was similar to the orthograde rate, but 5--10 times less label moved retrogradely. Autoradiographs showed that the retrograde label was localized to R3--R14 axons. This report clearly demonstrates the rapid, selective, and bidirectional transport of a free amino acid and provides further evidence that glycine may be used as a neurochemical messenter by neurons R3--R14.