Language Disorders 245Causation
Twin studies show that SLI is highly heritable. Studies of one large
family with a dominantly inherited form of language disorder identified
a mutation of the FOXP2 gene that affects the development of the brain
(and other organs). However, mutations at this site have not turned out
to be a common cause of SLI more broadly. Perhaps there are many rare
mutants of strong effect, or perhaps there are common genetic variations
that have small or moderate effects. It remains to be seen whether shared
genes account for the co-occurrence of SLI with reading difficulties and
autistic traits.
What about environmental risk factors for SLI? These have been harder
to identify. At one stage, it was thought that otitis media with effusion
(‘glue ear’) was a significant risk factor, but more recent studies sug-
gest that any effect is relatively slight. Likewise, theories suggesting that
growing up in a bilingual environment increases the risk of SLI, are not
supported by the limited evidence.
Varieties of language disorders
Several different aspects of language can be affected by developmental
language disorders (see Box 30.1). Language disorders include:
1 Phonologic-syntactic language disordersinvolve problems in the form but
not the content of language. The child wants to communicate and says
appropriate things, but there are problems with articulation or syntax,
or both. Some children havepure articulation problems without any
other language problems. Delay or deviance in speech-sound production
makes these children harder to understand, and may lead to teasing.
In cases ofexpressive language disorder, speech develops late and syntac-
tic structures are several years behind age level. Articulation is often
faulty too, but comprehension is within normal limits.Receptive language
Box 30.1Different aspects of language
Phonology/articulationrefers to the production of speech sounds.
Prosodyrefers to the expression and comprehension of those aspects of
communication that are mediated by tone of voice and by variation in the
way different syllables are stressed.
Syntaxrefers to the production and comprehension of grammatically correct
sentences.
Semanticsrefers to the ability to encode meaning into words and decode
meaning from words.
Pragmaticsrefers to the ability to use and decipher language in a way that is
appropriate to the wider social-interpersonal context, for example, drawing
on knowledge of the context to grasp a message that is implicit but not
explicit in the words themselves.