What is SLI?
This is a term used to describe language difficulties that are not caused by any known neurological, sensory, intellectual, or emotional deficit. It can affect the development of any aspect of language: e.g. vocabulary, grammar and discourse skills. Children with SLI may be intelligent and healthy in all regards except in the difficulty they have with language, hence the term ‘specific’, difficulties are specific to language. They may in fact be extraordinarily bright and have high nonverbal IQs – but not always! SLI is often referred to as heterogeneous – children with SLI are all very individual, making it harder to identify a ‘typical’ child with SLI. SLI is a disorder with long-term impact, it's not just a matter of late language acquisition or something that children can grow out of. Diagnosis – official The most well know diagnostic manual – DSM-1V does not use the term SLI but refers to the categories of mixed receptive-expressive language disorder or expressive language disorder – it states that scores on IQ tests should be ‘substantially below those obtained from standardized measures of nonverbal intellectual capacity’. The other main classification system ICD-10 refers to Specific developmental disorders of speech and language, describing them as ‘disorders in which normal patterns of language acquisition are disturbed from the early stages of development. The conditions are not directly attributable to neurological or speech mechanism abnormalities, sensory impairments, mental retardation, or environmental factors.’ The conventional definition, used in research studies includes an IQ of 85 or above. How the term is used now Over the years, a range of terms has been used to describe this group of children –specific developmental language disorder, SLI, developmental language disorder. This latter term has been used by the group editing the book arising out of the last Afasic Symposium where many of the keynote speeches discussed the nature and cause of SLI. They felt this term would ‘largely encompass the variety of terms used’ and stated that it described a group of children who ‘fail to acquire their native language at a typical rate, for no obvious reason…..not associated with any other developmental disorder, sensory impairment or cognitive delay’. They purposely avoided the term ‘specific’ as they felt that many of the children who took part in research studies were likely to have subtle differences outside the language system. They felt the boundaries between SLI and other disorders which involved language were frequently difficult to distinguish. Different types SLI is a very broad category, with some children having mild and transient expressive problems and others having severe and persistent difficulties with both receptive and expressive language.
How is it different to other types of Speech, Language and Communication Needs (SLCN)?
There are children with SLCN who are not considered to have SLI. Some children have poor or limited speech and language skills, lower than those of other children of the same age. Whilst they may have speech and language skills which are inadequate for the start of formal learning, with the right support they may catch up with their peers and therefore are not considered to have SLI. The number of children with this type of SLCN varies with location. In some areas, particularly areas of social disadvantage, this group may be upwards of 50% of children at school entry. Some children have speech, language or communication needs resulting from or co-occuring with other underlying impairments, for example, children with general learning difficulties, or other conditions, such as cerebral palsy, hearing impairment or autistic spectrum disorders. These children are not considered to have SLI; rather their needs arise as part of another condition.
How many children have SLI?
This depends upon which definition you use. The incidence of SLI was recently estimated in a study funded by the National Institutes of Health to be 7.6% among 5-year-old children.1
What causes SLI?
We know a lot more than we did even 30 years ago about the nature and cause of SLI, but there is still considerable uncertainty. We now know more about what are NOT causes of SLI: quantity and quality of language input, mild hearing loss, early brain injury. Most recent thinking is that people with SLI have a different genetic make-up. However this is not simple! We now know that genes play an important part in causing SLI but there is no biological diagnostic test. “The growing consensus is that in most cases of language impairment we will not be able to point the finger at a single causal factor; rather SLI is regarded as a complex multifactorial disorder, in which a collection of risk factors conspires to disrupt language development”.2 It is not a single gene disorder but likely to be patterns of variations in genes – or genetic mutations. There has been a lot of research around one family – a mutation has been found in approximately half the members of three generations (FOXP2) – however this has also been found to be entirely normal in other people with SLI. It is not a simple picture. SLI does run in families but it does not normally show clear cut patterns of inheritance – we look for the influence of many genes, combined with environmental factors. Some researchers are focusing on looking at genetic influences on different types of SLI.
See the entry for SLI on Talking Point website. |