Does my child have dyslexia?
If you have a child with a speech or language disorder, you have probably heard that they are “at risk” for future learning disabilities. What are the prevalency rates though, and what does the actual research tell us?
A study by Catts (1993) is a frequently cited study and found that,
The literacy outcomes of children with SSD (speech sound disorder) have provided convincing evidence that children with SSD and concomitant LI (language impairment) (SSD+LI) have higher rates of literacy difficulties than children with isolated SSD.
So what does this mean? How high are the higher rates and what exactly are “literacy difficulties?”
In 2004, Lewis et.al followed 10 children diagnosed with CAS (Childhood Apraxia of Speech) and compared literacy outcomes for them into the school aged years along side kids who were diagnosed with SSD (speech sound disorder) and another group who had SSD + LI (language impairment). At follow up, all 10 children with CAS demonstrated co-morbid disorders of reading and spelling. This was a small sample size, but let me reiterate, ALL TEN children with CAS had future problems with reading and spelling. Co-morbid rates though can’t be 100% right?
A study in 2011 by Anthony et.al found that,
Children with SSDs are at increased risk of having difficulties learning to read (Bird, Bishop, & Freeman, 1995; Bishop & Adams, 1990; Carroll & Snowling, 2004; Catts, 2001; Larivee & Catts, 1999; Raitano et al., 2004; Roberts, 2005; Snowling, Bishop, & Sothard, 2000). In fact, between 30% and 77% of children with SSDs struggle with reading (Bird et al., 1995; Larrivee & Catts, 1999; Lewis, 1996; Nathan, Stackhouse, Goulandris, & Snowling, 2004). Children with SSDs have as high a risk of developing a reading disability (RD) as children with a family history of RD (Carroll & Snowling, 2004), which is remarkable in light of heritability estimates for RD that range from 40% to 70% (e.g., Friend, Defries, & Olson, 2008; Pennington, 1989). The risk of children with SSDs having literacy problems increases with comorbid language disorders (Nathan et al., 2004; Raitano et al., 2004), severity of the SSD (Nathan et al., 2004), persistence of the SSD (Nathan et al., 2004; Raitano et al., 2004), and patterns of articulation errors that do not follow developmental trajectories (Leitão & Fletcher, 2004; Leitão, Hogben, & Fletcher, 1997; Mann & Foy, 2007; Rvachew, Chiang, & Evans, 2007).
A study by McNeill (2009) found:
The results indicated that the CAS group had inferior phonological awareness than the ISD and typical development groups. The CAS group had a greater proportion of participants performing below their expected age level than the comparison groups on phonological awareness, letter–sound knowledge and decoding tasks. There was no difference in the performance of the CAS and ISD groups on the phonological representation task.
In this study, speech sound disorders are all lumped together. Speech sound disorders include: phonological disorder, articulation disorder, and apraxia. Depending on the study, anywhere between 30% to as high as 77% of children with a “Speech Sound Disorder” have difficulty learning to read. That’s the quite the gap right? There is almost a 50% discrepancy between studies. So what gives? Who is more at risk?
We know every co-morbidity(which is a fancy word for additional diagnoses) increases the risk. This especially includes children who have a language disorder. This includes kids diagnosed with “mixed receptive/expressive language disorder,” SLI (specific language impairment), language disorder, or language processing disorder
I also bolded the phrase “patterns of articulation errors that do not follow developmental trajectories,” because up until 2007, apraxia was not officially recognized as a distinct childhood speech disorder by the American Speech Language Hearing Association. This is only relevant because the studies this data is taken from all are around 2007 and before; and if you know what apraxia is, it is a speech sound disorder, but also a motor planning disorder that does not present with patterns of errors and may or may not follow developmental norms for articulation. In the above information, that EXACT description increases the risk for a reading disorder.
The most recent research is now indicating dyslexia is a phonological processing disorder that parallels the core phonological deficit in speech sound disorders (Anthony et al., 2011). This research is groundbreaking because before we knew the risk for reading disability was higher in kids with SSD’s, but we didn’t have research telling us why.
The bottom line though is this.
Any childhood speech and language disorder increases the risk for a future reading disability.
It would appear that children with CAS are at an increased risk, and those with CAS plus a language impairment or comorbid phonological disorder, are even more at risk.
Are all reading disabilities then dyslexia? The short answer is no, but dyslexia is by far the most common reading disability and can manifest in varying severities. If you read research articles, reading disorder and dyslexia are almost synonymous. For example in the 2004 article by Vellutino et al., this is the opening statement.
We summarize some of the most important findings from research evaluating the hypothesized causes of specific reading disability (‘dyslexia’) over the past four decades.
According to the National Institute of Child Health and Human Development, “reading and language based learning disabilities are commonly called dyslexia,” and according to the International Dyslexia Association,
15-20% of the population has a language-based learning disability. Of the students with specific learning disabilities receiving special education services, 70-80% have deficits in reading. Dyslexia is the most common cause of reading, writing and spelling difficulties. Dyslexia affects males and females nearly equally as well as, people from different ethnic and socio-economic backgrounds nearly equally.
The schools do not diagnose dyslexia, although they give all the same tests that learning centers give to diagnose it. Schools are an educational entity, and thereby give “educational” diagnoses. The educational diagnosis for dyslexia is specific learning disability. Knowing prevalency data and co-morbidities better equips special education teachers, parents, and other professionals to implement treatment strategies that can include pre-cursory and preventative measures to address potential and additional difficulties later in the child’s academic career.