Can a urine test diagnose autism?
“A simple test that would revolutionise the diagnosis of autism is being developed by British scientists,” the Daily Mail reported. The test would need just a few drops of urine, and is based on the idea that people with autism have different bacteria in their guts from those without autism.
This research compared the chemical profiles of urine samples from a small group of autistic children to those from their non-autistic brothers and sisters, and another group of unrelated non-autistic children. It did find that autistic children had differences in the levels of some chemicals, but those that were most different are not chemicals produced by gut bacteria.
This is encouraging research, but it is too early to say whether it will develop into another diagnostic tool for autism. Importantly, it did not directly investigate the role of gut bacteria in autism, but looked at levels of chemicals in urine. Also, it is not possible to determine whether these differences indicate a cause or consequence of autism. These children were already diagnosed with autism, and the study used urine samples from only one point in time. Further research in a larger group of children over time is needed.
Where did the story come from?
The study was carried out by researchers from Imperial College London and the University of South Australia. It was funded by Cure Autism Now and a grant from the International Study of Macro-Micronutrients and Blood Pressure. The study was published in the peer-reviewed_ Journal of Proteome Research._
The Daily Express reported that this study had distinguished children with autism by “looking at bugs from their intestinal tracts and the body’s metabolic process in their urine”. The Daily Mail reported that the test “builds on research showing that people with autism have different bacteria in their guts from others”. Additionally, The Daily Telegraph focused on the gut bacteria being a potential therapeutic target based on this research.
However, the research did not actually make any direct measurements of gut bacteria. The extent to which the chemical composition of urine reflects the bacterial population in the gut was not demonstrated in this study.
What kind of research was this?
This was a cross-sectional analysis, in which the researchers conducted chemical analysis of urine samples from children who had been diagnosed with autism, their non-autistic siblings and children without autism. The researchers aimed to assess whether there was any difference in the chemical composition of the urine samples from these children.
What did the research involve?
Urine samples from autistic children, their siblings and unrelated non-autistic children were obtained from the University of South Australia. Further urine samples from non-autistic children were also collected from Switzerland. The children were between three and nine years old. Children with autism met psychiatric criteria for autism disorder or Asperger syndrome.
There were 35 samples from autistic boys and four from autistic girls. The ‘sibling group’ was made up of 17 brothers of these children and 17 of their sisters. The control group consisted of 17 samples from non-autistic boys and 17 from non-autistic girls.
To identify the different types of chemicals in the children’s urine the researchers used a technique called nuclear magnetic resonance spectroscopy.
What were the basic results?
Initial analysis of the chemicals in the urine samples showed that the major source of variation between them was not related to autism, but variation between individuals. However, further statistical analysis indicated that the chemical pattern was different in the autistic children compared with non-autistic children and was partially different between the siblings and the non-autistic children.
The researchers then assessed whether the types of chemical found in the urine samples differed between each group. This analysis involved a statistical test that compared all of the chemicals in the children’s samples at the same time rather than assessing each chemical separately. This showed there were higher levels of some chemicals in autistic than non-autistic children, and vice versa.
For example, autistic children had higher levels of the breakdown products of nicotinic acid, N-methyl nicotinic acid (NMNA), and N-methyl nicotinamide (NMND), but lower levels of chemicals that are suggested to be associated with gut bacteria such as hippurate and phenylacetylglutamine (PAG).
The urine samples of the siblings of the autistic children were not significantly different to those of either of the other groups.
Statistical analysis of individual chemicals showed that autistic children had higher levels of NMNA and NMND compared with non-autistic children. NMNA and NMND, and succinate were also higher in the autistic children’s samples compared with those of their non-autistic siblings. Chemicals typically associated with gut bacteria, such as hippurate and phenylacetylglutamine (PAG), were no longer significantly different between autistic and non-autistic children.
How did the researchers interpret the results?
The researchers suggest that there are significant differences in the metabolic composition of urine between children with autism and unrelated non-autistic children. They say that the breakdown products of nicotinic acid (NMNA and NMND) were the group of chemicals that had the greatest power to indicate differences between autistic and non-autistic children.
However, they say that larger scale, longitudinal studies are needed to determine “whether the metabolic differences are related to the cause or the progression of the disease”.
Conclusion
This small study showed that there were differences between the chemicals in urine samples from autistic children compared with non-autistic children, however there was a degree of variation between all of the children’s samples regardless of whether they had autism or not. Further work is required to see whether the observed differences are consistent in a larger sample. Although the researchers suggest that some chemicals found in urine may be associated with bacteria in the gut, measuring chemicals in urine samples is an indirect way of assessing whether gut bacteria are associated with autism.
The research has several limitations:
- The researchers point out that, as it is not possible to tell whether these differences indicate a cause or consequence of the disease, further research is needed in a larger group of children over time.
- Different statistical analyses had different results, some showing differences in certain chemical levels in autistic children, while others did not.
- The researchers did not assess the medications the children with autism were taking for their condition or the diet they were following. Both would affect the chemicals they found in the children’s urine samples.
Finally, these children had already been diagnosed with autism, and the study design was cross-sectional, looking at their urine samples from only one point in time. It is not possible to say whether there would be any differences in the chemicals found in the urine in younger children prior to standard diagnosis, and whether it could be used as a diagnostic tool.
This is encouraging research, but it is too early to say whether this research would be of benefit in terms of providing an additional diagnostic tool for autism in children.
