Potential Causes of Developmental Language Disorder
Rather than a single cause, developmental language disorder (DLD) is caused by multiple risk factors working together. Parents should not feel a sense of guilt for their child’s DLD since these risk factors are, with few exceptions, beyond our control.
Genetic Factors Contributing to DLD
DLD often runs in families. Each person has many thousands of genetic variations that can interact to influence how the brain develops. If parents have enough of these DNA changes affecting parts of the brain that are important for language, the child may have DLD. Scientists call this polygenic risk because it’s the combined effect of many genes.
Less commonly, a child with DLD may be born to parents who don’t have this polygenic risk related to language. In these cases, it's possible that the child may have a very severe DNA mutation in a gene that is critical for brain and language development. Scientists call this a de novo mutation because it is a new mutation in the child that is not shared with the parents. In these cases, the child is likely to be quite different from his or her siblings in terms of language ability.
Environmental Factors Associated with DLD
Genes alone do not determine outcomes. The environment also plays a role. We know, for example, that children who lack certain nutrients in their diet can be at higher risk for DLD than other children. Things that happen during pregnancy or birth may also influence a child’s brain and eventually his or her ability to use language effectively. For example, if a child is born prematurely, or on time but at a low birth weight, or experiences a lack of oxygen to the brain, they may have increased risk for language difficulties later on. It’s important to note that some of these sorts of complications might also have a genetic component.
Other Developmental Conditions Associated with DLD
Other well-characterized developmental conditions, like autism or intellectual disability, have an influence on a child’s language ability. The preferred name for this kind of language disorder is Language Disorder associated with X, where X is the name of the developmental condition. These conditions are largely genetic and, like DLD, often result from some combination of polygenic risk and de novo mutations (see above).
As with DLD, the environment also plays a role in Language Disorders associated with other developmental conditions. For example, a language problem caused by alcohol exposure in the womb is Language Disorder associated with Fetal Alcohol Syndrome.
Parents should know that although genes are very important for language ability, our current knowledge is no more useful for family planning purposes than a careful look at both partners' family history. Even in autism, where genetic research is much farther along than for DLD, only about 10% of families participating in research received a genetic result that was considered clinically relevant. As scientists learn more about how genes influence the brain's development, these numbers will grow for both autism and DLD.
For scientists, understanding genetic and environmental risks can lead to new insights into the biology of language. These new insights could improve treatment options. For parents, a better understanding of the risk factors and their biological roots can help to demystify the experience of raising a child with language difficulties.
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