Kathryn discusses developmental language disorder with speech and language therapist Christian Wright. He says in every primary school classroom there will be around two children affected by the condition.

Developmental language disorder (DLD) is a brain-based condition that affects around two children in every primary school.

Diagnosis is important because if untreated this condition can lead to severe difficulties later in life, says speech and language therapist Christian Wright.

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Kids with DLD have difficulty both expressing themselves and understanding others, Wright tells Nine to Noon.

They may make speech sounds that are unclear, but this isn't necessary for a diagnosis.

"Certainly it's a language-based issue. It's not associated with other known conditions like autism, hearing loss, cerebral palsy, Down syndrome. Children who have language issues with those conditions, we would just say that they have a concomitant language issue, but it's very much a condition that stands alone.

"So your hearing is fine. Typically, their cognition is quite good. But they have these language difficulties and it's a lifelong condition. It's often discovered in childhood and that's often where we'd like to start treating it. But it persists for many into the adult years and these are the children who have these language difficulties as pre-schoolers."

If a child's self-expression and understanding is impaired when they start school, they begin with language levels significantly lower than their peers, Wright says.

"It's often characterised by spoken language difficulties like limited vocabulary, poor grammatical development. Like a boy I was working with the other day who's almost five. Instead of saying 'that boy is riding his bike really fast' he said to me, 'him doing bike'. completely truncate the sentence and oversimplify the language."

Difficulties with understanding seem to go along with poor working memory, he says.

If we imagine working memory as a series of slots that we can put information into temporarily, these children have a significantly restricted number of slots.

"So, if it were like a window, it's a tiny window through which you have to push information because they keep losing a lot of what they're understanding."

Wright says it is not known why some children have this condition and some don't, but there is a suggestion that it may run in families.

"It looks like there's some kind of combined impact of inherited genes, rather than a specific mutation…

Go to this episode on rnz.co.nz for more details