region and are closely associated with autism .
The gene linked to fragile X syndrome lies on the X chromosome . Its name ,
FMR 1 , is easily forgettable , but the effects of its variants are not . Studies on the causes of fragile X reveal that the protein this gene encodes , FMRP , acts as a cellular shuttle for RNA molecules that are crucial for nerve-cell communication and plasticity of connections in the brain . In people with fragile X , cells don ’ t produce the protein , or make very little of it . The
Like FMR 1
, the genetic changes involved in Rett syndrome also affect brain development . A gene called methyl CpG binding protein 2 , or
MECP 2
, mutations that affect its function can lead to broad effects . Some of the resulting features look so much like autism that Rett syndrome was categorized as an autism spectrum disorder until 2013 .
Other genetic syndromes also include autism as a feature .
Children with fragile X syndrome carry X chromosomes with an abnormality at the tip of one of the chromosome arms , as shown in this illustration ( normal X on the left , abnormal X on the right ). This affects a gene called FMR1 , which carries instructions for a protein important for brain activity , such that little or none of the protein is made . Fragile X is associated with a range of developmental disabilities , often including autism .
CREDIT : MONICA SCHROEDER / SCIENCE SOURCE
Some are caused by variants in a gene called
SHANK 3 which , like most genes implicated in autism , is involved in brain development and function . The protein that it encodes helps to coax nerve extensions to form and take shape so that a nerve cell can communicate with others . The SHANK3 protein also provides a physical scaffold for those cells to link up . In populations of people with mutations that prevent SHANK3 protein production or who are missing the segment of chromosome 22 that contains the gene , most will have autism or
Phelan- McDermid syndrome , which often includes autism .
Despite their clear ties to autism , these syndromes are rare . “ Collectively , they are found in about 5 percent of the total population of patients with autism ,” Gozzi says . That leaves a great deal to explain .
Inheritance on a spectrum So where do the other autistic people come from , genetically speaking ? Robinson says that their genetics don ’ t neatly fall into two types of buckets , of either a few genes with big effects or many genes with small effects . “ It ’ s been well established at this point that it ’ s not either – or ,” she says . In fact , says Gozzi , varying
To Table of Contents
Accessibilty for All 49