The exact number of children with autism is unknown. However, when I was born, autism affected 1 in 5000 children in the U.S. In 2014, that number surged to 1 in 68, a 7253% increase in one generation and a 30% rise from the estimate just two years earlier.62, 63 Newer estimates in 2018 show that autism affects 1 in 59 children. This marks a 15 percent increase from two years prior, and the highest prevalence since the CDC began tracking ASD in 2000.
What is autism? What is autism spectrum disorder (ASD)?
Autism and Autism Spectrum Disorder (ASD) are general terms for a complex developmental disorder that affects the brain’s social, behavioral, and communication skills. It is a physical condition linked to abnormal biology and brain chemistry, and it typically appears during the first three years of life. The characteristic traits of autism are repetitive behaviors and impaired social-emotional interaction. Each ASD case is different: 25% of people with ASD are nonverbal (learning to communicate in other ways), while roughly 40% have average to above-average intellectual abilities. Many people on the spectrum take pride in their “atypical” view of the world and some exhibit exceptional abilities in music, math, or academics.
How common is autism?
In 2014, about 1 in 68 children were identified with autism spectrum disorder (1 in 42 boys and 1 in 189 girls). In 2012, 1 in 88 children were identified as on the spectrum—a tenfold increase over the last 40 years with boys nearly five times more likely to be diagnosed with ASD than girls. ASD is reported across all racial, ethnic, and socioeconomic groups.
Tracking autism over time has shown distinct challenges:
- The nature of the disorder is extremely complex.
- There are no specific biological markers for autism.
- Reporting and diagnostic tools for ASDs have changed over time.62
Signs of autism
Autism spectrum disorders (ASDs) can range in intensity from very mild to severe, affecting individuals in different ways. Some children with an ASD may show hints of future developmental delay within the first few months of life; however, the most obvious signs of autism tend to appear between 18 months and three years old. Most pediatricians will use a formal screening tool or checklist for autism when your child is 18 and 24 months old.63, 64
A child with an ASD might…
- Not respond to their name by 12 months
- Not point at objects to show interest (point at an airplane flying over) by 14 months
- Not play “pretend” games (pretend to feed a doll) by 18 months
- Avoid eye contact and want to be alone
- Not look at objects when another person points at them
- Have trouble understanding other people’s feelings or talking about their own feelings
- Have delayed speech and language skills
- Prefer not to be held or cuddled or might cuddle only when they want to
- Repeat words or phrases over and over (echolalia)
- Give unrelated answers to questions
- Get upset by minor changes
- Have trouble adapting when a routine changes
- Have obsessive interests in single subjects (like cars or trains)
- Flap their hands, rock their body, or spin in circles
- Have unusual reactions to the way things sound, smell, taste, look, or feel
- Lose skills they once had (for instance, stop saying words they were using previously)
- Have chronic bowel or gastrointestinal issues, such as diarrhea or chronic constipation. Up to 80% of children with ASDs have gastrointestinal (GI) abnormalities.
What if I think my child has an ASD?
- If you suspect a problem, talk with your child’s doctor and ask for a developmental screening. Early detection is linked to better outcomes for children with an ASD. Your doctor may refer you to a multidisciplinary team for further evaluations. The following professionals can give a diagnosis of autism: developmental pediatrician, child psychiatrist, child psychologist, or pediatric neurologist.
- Contact your local Early Intervention (EI) agency for children under three years old, or public school system for children three years and older. Currently the main research-based treatment for an ASD is intensive structured teaching of skills, often called behavioral intervention or behavior analysis. It is important to begin this intervention as early as possible in order to help a child reach his or her full potential.
What causes autism?
Autism has no single cause. However, it is likely that both genetics and environmental factors play a role. Within the last five years, scientists have identified a number of gene mutations or irregular segments of genetic code linked to autism. Research indicates that the majority of genetic risk for autism comes from common gene variants rather than from spontaneous gene mutations (which make up a very small number of cases). Further understanding the genetic risk for autism can lead to a better understanding of the molecular roots of the disorder.65
Other studies of autism show abnormalities in the brain that likely occurred as a disruption during early fetal brain development, possibly due to environmental influences. The study of epigenetics describes how environmental factors affect certain genes, altering gene expression without changing the underlying DNA. Several studies on identical twins have supported that gene-environment mechanisms are likely at play, since identical twins sharing exact DNA show varying levels of ASD severity. To note, the term “environmental factors linked to autism” covers a multitude of influences outside of a child’s inherited genes, ranging from chemical exposure to other factors, such as premature birth and low birth weight. Finally, while scientists do see commonalities among ASD cases, they do not yet fully understand how all of the pieces – genetic, immunologic, nutritional, and environmental – fit together in the autism puzzle.66, 67
Genetic vulnerability
No one gene causes autism, and many people with ASD have no reported family history of autism. However, twin and family studies suggest that most individuals have a genetic predisposition to autism.
- Identical twin studies show that if one twin is affected by autism, there is a 60 to 90% chance that the other twin will be affected.63
- Parents from families with autistic members are more likely to have autistic children, and families with one autistic child have a 3 to 14% greater chance of having another autistic child, a greater percentage chance than the population at large.
- The California Autism Twins Study (CATS), the largest study of twins with ASDs, found that when one identical twin develops autism, the chance of the other twin developing the disorder is 70%, while fraternal twins overlapped by a surprising 35% (significantly higher than the 3 to 14% for different age siblings). This provides evidence to support the claim that genes and certain environmental influences, especially those shared in the womb or shortly after birth, are likely at play.68
- Autism also tends to occur more frequently than expected among individuals who have certain medical conditions, including Fragile X syndrome, tuberous sclerosis, congenital rubella syndrome, and untreated phenylketonuria (PKU).
Environmental factors
The rapid rise in autism over the last twenty years cannot be linked solely to genetics. The human genome does not change that rapidly. Gene-environment interactions are likely happening:
- Some risk factors more closely associated with autism are:
- Toxins ingested during early pregnancy
- Infection during pregnancy
- Maternal diabetes
- Birth complications, especially those involving oxygen deprivation to the brain
- Other factors under investigation include:
- Advanced parental age 69, 70
- Premature birth and low birth weight 71, 72
- Pesticide exposure during pregnancy 73
- Pharmaceuticals taken during pregnancy 74
- Proximity to a freeway 75
- Limited prenatal vitamin intake 76
- Radio waves from cell phones (low frequency cell phone signals are harmful to cell function allowing heavy metal toxins to build up)77
- Increased surveillance and broadening of the ASD definition 78, 79
- Scientists are looking closely at environmental exposures during pregnancy and shortly after birth. Children with autism may have particular vulnerabilities and metabolic impairment at this time that reduces the ability to process and rid the body of toxins.
- Some of the most powerful evidence for environmental factors causing autism is derived from studies of specific prenatal exposures: thalidomide, misoprostol, and valproic acid; maternal rubella infection; and the organophosphate insecticide chlorpyrifos.74
- In another study, analysis of brain tissue from ten out of eleven children, who died and also happened to have autism, found that ASD was likely to have originated before birth. This conclusion was based on a disruption of tissues in the cortex areas that likely occurred during early brain formation (from three to five weeks after conception to the second trimester) when brain cells specialize and move into their correct positions in the cerebral cortex.80 These types of studies, including those with small sample sets, are particularly illuminating since scientists can look at the autistic brain on a cellular level.
- Finally, it is possible there are undiscovered environmental causes of autism.
Sources
62. Centers for Disease Control and Prevention. Autism Spectrum Disorder (ASD): Data & Statistics. April 17, 2014; Available from: http://www.cdc.gov/ncbddd/autism/data.html.
63. National Institute of Neurological Disorders and Stroke. Autism Fact Sheet. April 14, 2014; Available from: http://www.ninds.nih.gov/disorders/autism/detail_autism.htm.
64. Lemcke, S., et al., Early signs of autism in toddlers: a follow-up study in the Danish National Birth Cohort. J Autism Dev Disord, 2013. 43(10): p. 2366-75.
65. Gaugler, T., et al., Most genetic risk for autism resides with common variation. Nat Genet, 2014. 46(8): p. 881-5.
66. Wong, C.C., et al., Methylomic analysis of monozygotic twins discordant for autism spectrum disorder and related behavioural traits. Mol Psychiatry, 2014. 19(4): p. 495-503.
67. LaSalle, J.M., A genomic point-of-view on environmental factors influencing the human brain methylome. Epigenetics, 2011. 6(7): p. 862-9.
68. Hallmayer, J., et al., Genetic heritability and shared environmental factors among twin pairs with autism. Arch Gen Psychiatry, 2011. 68(11): p. 1095-102.
69. Reichenberg, A., et al., Advancing paternal age and autism. Arch Gen Psychiatry, 2006. 63(9): p. 1026-32.
70. Idring, S., et al., Parental age and the risk of autism spectrum disorders: findings from a Swedish population-based cohort. Int J Epidemiol, 2014. 43(1): p. 107-15.
71. Schieve, L.A., et al., Population attributable fractions for three perinatal risk factors for autism spectrum disorders, 2002 and 2008 autism and developmental disabilities monitoring network. Ann Epidemiol, 2014. 24(4): p. 260-6.
72. Schendel, D. and T.K. Bhasin, Birth weight and gestational age characteristics of children with autism, including a comparison with other developmental disabilities. Pediatrics, 2008. 121(6): p. 1155-64.
73. Shelton, J.F., et al., Neurodevelopmental Disorders and Prenatal Residential Proximity to Agricultural Pesticides: The CHARGE Study. Environ Health Perspect, 2014. 122(10): p. 1103-9.
74. Landrigan, P.J., What causes autism? Exploring the environmental contribution. Curr Opin Pediatr, 2010. 22(2): p. 219-25.
75. Volk, H.E., et al., Residential proximity to freeways and autism in the CHARGE study. Environ Health Perspect, 2011. 119(6): p. 873-7.
76. Schmidt, R.J., et al., Maternal Intake of Supplemental Iron and Risk of Autism Spectrum Disorder. Am J Epidemiol, 2014. 180(9): p. 890-900.
77. Carlo, G.L. and R.S. Jenrow, Scientific progress – wireless phones and brain cancer: current state of the science. MedGenMed, 2000. 2(3): p. 40.
78. Rutter, M., Incidence of autism spectrum disorders: changes over time and their meaning. Acta Paediatr, 2005. 94(1): p. 2-15.
79. Taylor, B., Vaccines and the changing epidemiology of autism. Child Care Health Dev, 2006. 32(5): p. 511-9.
80. Stoner, R., et al., Patches of disorganization in the neocortex of children with autism. N Engl J Med, 2014. 370(13): p. 1209-19.