Prevalence of autism in children of Somali origin living in Stockholm: brief report of an at-risk population
Abstract
This work was a follow-up study (birth years 1999–2003) of the prevalence of autism in children of Somali background living in the county of Stockholm, Sweden. In a previous study (birth years 1988–98), the prevalence of autism associated with learning disability**
UK usage for mental retardation.
was found to be three to four times higher among Somali children compared with other ethnicities in Stockholm. We examined all records of children of Somali background, born from 1999 to 2003, registered at the centre for schoolchildren with autism and learning disability. The census day was 31 December 2009. The prevalence of autism and PDDNOS (with learning disability) was 0.98% (18/1836) in the Somali group and 0.21% (232/111 555) in the group of children of non-Somali origin (p<0.001). The increased prevalence remained and was now between four and five times higher in children of Somali background. A clinical observation was that more than 80%, in addition to autism and learning disability, had a profound hyperactivity. The findings accord with many other studies reporting higher prevalence rates of autism in children of immigrant mothers. We discuss the need for further research of underlying mechanisms.
Abbreviations
-
- ASD
-
- Autism spectrum disorder
-
- PDDNOS
-
- Pervasive developmental disorder not otherwise specified
In a previous study we reported an increased prevalence of autism in children of Somali origin residing in the county of Stockholm, Sweden.1 The prevalence among these children born from 1988 to 1998 was three to four times higher than that among children of non-Somali origin. The same tendency has been reported (unpublished data) from Minnesota, USA, and from Canada. The reasons for this increase are not known. However, many European studies have reported an increased frequency of autism in children of immigrant mothers. Thirty years ago, Wing2 suggested that autism might be more common in children born to immigrant parents. Findings supporting this observation were also reported from western Sweden.3
In a recent study from the UK, mothers born outside Europe had a significantly higher risk of having a child with an autism spectrum disorder (ASD) than mothers born in the UK. Immigrants from the Caribbean, followed by those from Africa, had the highest risk.4
The increased rate of children with autism in the Somali population living in Stockholm has attracted attention from the National Board of Health and Welfare in Sweden. The Board has declared ASD in the Somali population in Sweden a prioritized area of research. The aim of the present work therefore was to perform a new prevalence study in the same county in a previously unstudied birth year cohort (1999–2003). We wanted to establish that the high rate of ASD in children born to mothers of Somali origin reported by us a few years ago was not a chance finding.
The study was approved by the ethics committee at Karolinska Institutet.
In the county of Stockholm (with a total population of about 2.0 million people and about 22 000 births per year during the studied period), all children from the age of 6 years (school age) with a diagnosis of autism or pervasive developmental disorder not otherwise specified (PDDNOS; Diagnostic and Statistical Manual of Mental Disorders, 4th edition),5 and an associated verified learning disability (with IQ under 70), are referred to a specialized centre for habilitation, the Autism Centre for Schoolchildren in Stockholm.
Records, held at this centre, of children of Somali origin and with birth years 1999 to 2003 were scrutinized for sex, country of birth, diagnosis of ASD, methods of assessment, associated diagnoses, activity level, motor function and, if possible, aetiological diagnosis.
Children of Somali background were those who were born either in Somalia or in Sweden, with both parents born abroad and at least one parent coming from Somalia, as defined by the Swedish Central Bureau of Statistics.6
On the census day (31 December 2009) there were 113 391 children born from 1999 to 2003 living in Stockholm county, and 1836 of these were of Somali origin. A total of 250 children with birth years 1999 to 2003 were registered at the Autism Centre for Schoolchildren on the census day. There were no children with Asperger syndrome registered at this centre. Eighteen children with autism/PDDNOS (13 males, five females) of Somali origin, born between 1999 and 2003 (6–10y of age on the census day), were identified. Of the 18 children, 15 had autistic disorder and three had a PDDNOS/autistic-like condition; all had learning disability. Most (16/18) had been born in Sweden.
The prevalence of autism and PDDNOS (with learning disability) was 0.98% (18/1836) in the Somali group and 0.21% (232/111 555) in the group of children of non-Somali origin (p<0.001). At the centre, children of Somali origin constituted 7.2% (18/250) compared with a rate of 1.6% (1836/113 391) among the total child population with birth years 1999 to 2003 (p<0.001).
At the time of the present study, 15 of the 18 children had notes in their medical records referring to increased activity level and were described as having marked hyperactivity, attention-deficit–hyperactivity disorder, or ‘attention-deficit–hyperactivity disorder-like symptoms’.
Two of the Somali children had siblings with diagnosed autism (and learning disability). Another two of the children had siblings with developmental disorders other than ASD. These are minimum figures for ‘familial autism’ given that we cannot be certain that data for sibling, parent, or other relatives were systematically recorded in all instances.
We could not find evidence in the routine medical records that a definitive aetiological diagnosis had been made in any of the 18 children of Somali origin.
The high prevalence of autism in children of Somali origin in Stockholm county reported in our previous study was confirmed in this new cohort of younger children. The prevalence in the new birth-year cohort was 4.7 times higher than that of the general population, and 4.5 times higher at the specialized autism centre. If anything, there was trend towards an even higher prevalence rate in this study compared with that performed a few years ago. Clinically, the most remarkable feature of the children with autism of Somali origin was hyperactivity, reported in 15 of the 18 children (83%). Attention-deficit–hyperactivity disorder is commonly associated with ASD, and co-occurrence has been reported in 30–80% of children with ASD.7 However, in this Somali population, our clinical impression was that the hyperactivity/attention-deficit–hyperactivity disorder that occurred in most of the children was exceptionally marked.
We have shown8 that mothers of Somali origin have much lower levels of vitamin D than do Swedish-born mothers in Stockholm county. Experimental studies of developmental vitamin D deficiency have been reported to influence dopamine turnover during brain development.9 It has also been found that adult rats exposed to vitamin D deficiency during brain development show novelty-induced hyperlocomotion, which can be ameliorated by pretreatment with the antipsychotic drug haloperidol.10
In conclusion, our findings support the increased prevalence of autism in children of Somali background. A striking clinical observation was that more than 80% had a profound hyperactivity, in addition to autism and learning disability. Further studies of vitamin D are needed, as well as other (including genetic) studies pertaining to possible risk factors in this population.
What this study adds
- •
We examined all records of children of Somali background living in Stockholm, Sweden, born from 1999 to 2003, registered at a centre for schoolchildren with autism and learning disability.
- •
The findings accord with many other studies reporting higher prevalence rates of autism in children of immigrant mothers.
Footnotes
Acknowledgements
We are grateful to the staff at the Autism Centre for Schoolchildren in Stockholm.
