Learning difficulties and academic achievement

It is estimated that 20% to 75% of children with NF1 experience some sort of learning disability (LD) (Vogel et al., 2017); making it one of the most frequently reported complications of the disorder (Lehtonen et al., 2013). The current definition of a LD or specific learning disorder (SLD), according to the DSM-5 (American Psychiatric Association, 2013), is that; a) there are significant difficulties in academic abilities (e.g. reading, written expression, mathematics) which have been present for at least six months despite targeted intervention; b) the affected academic abilities are significantly below age expectations and impact on academic, occupational or everyday functioning; c) the onset of difficulties occurs during school-age years and d) the difficulties are not better explained by other disorders (e.g. intellectual

disability, auditory/visual disturbance, neurological conditions) or adverse conditions (e.g. psychosocial adversity, inadequate instruction). In contrast, the previous

definition of a LD according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revised (DSM-IV-TR; American Psychiatric Association, 2000) was performance falling significantly below that expected according to an individual’s age, schooling and intellectual functioning on a

standardised measure of academic abilities (i.e. reading, spelling, written expression, mathematics). In line with this DSM-IV-TR (American Psychiatric Association, 2000) definition, several NF1 studies defined LD as a significant discrepancy between intellectual functioning (IQ) and academic achievement (Dilts et al., 1996; Hofman et al., 1994; Hyman et al., 2005; Mazzocco et al., 1995; Watt et al., 2008). Although there are often differences between studies around the interpretation of what a significant discrepancy is (Hyman et al., 2006; Krab, Femke, et al., 2008; Orraca- Castillo et al., 2014). In contrast, some studies simply defined LD according to

absolute performance scores (North et al., 1995). As a result of this wide range of definitions, there is great variability in the reported incidence of LD/SLD in children with NF1 (Lehtonen et al., 2013).

In a study conducted by North et al. (1995), 65% of 40 school-age children with NF1 had an impairment in reading, spelling or mathematics. Impairment in reading and spelling was defined as performing at least two years below chronological age norms. Impairment in mathematics was defined as performance less than 1.96 standard deviations below the mean (North et al., 1995). In a later study, Hyman and

colleagues (2006) defined SLD as academic difficulties (performance score falling at least 1 SD below the mean) being present in an individual with normal IQ. This is in contrast to a general learning disability (GLD) which they defined as a low IQ (≤80) and poor academic achievement without a significant IQ-achievement discrepancy (Hyman et al., 2006). Using these criteria, their results indicated that of a sample of 81 children with NF1, 20% met the criteria for a SLD, 32% could be classified as having a GLD and the remainder were functioning normally academically.

Interestingly there was a significant gender effect with almost all of those diagnosed with an SLD being males (15 out of 16) (Hyman et al., 2006). Thus Hyman et al. (2006) concluded that males with NF1 are at a much greater risk of SLD, while females with NF1 are at no greater risk than those in the general population.

Learning difficulties have also been reported in children with NF1 where their first language is not English. In a Dutch study, teacher questionnaires were used to examine the academic performance of Dutch children aged between seven and 17 years (Krab, Femke, et al., 2008). They reported that 75% of children were displaying significant difficulty (performance 1 SD below normative mean) in at least one

academic area. In addition, children with NF1 had a four-fold greater risk for

attending special education (Krab, Femke, et al., 2008). Another study examined the incidence of reading (developmental dyslexia) and maths (developmental dyscalculia) LD in 32 Spanish-speaking children with NF1 (Orraca-Castillo et al., 2014). Using criteria of at least two SD below the normative mean and normal intellectual functioning they reported that 18.8% had dyscalculia and 50% had dyslexia. A

significant gender difference was found for the incidence of dyscalculia with the male to female ratio reported as 5:1. There was no gender difference in the incidence of dyslexia (Orraca-Castillo et al., 2014).

2.2.3.1 Mathematics

As described previously, school-age children with NF1 are at greater risk of a range of learning difficulties including specific academic impairments in reading, spelling and writing. These literacy difficulties are described in more detail in section 2.4. In addition to literacy difficulties, children with NF1 are also at increased risk for difficulties related to mathematics (Levine et al., 2006). Study findings indicate that children with NF1 perform more poorly on general mathematics measures compared to age/grade norms (De Winter, Moore, Slopis, Ater, & Copeland, 1999; Hofman et al., 1994; Krab, Femke, et al., 2008; Lehtonen et al., 2015) and unaffected siblings (Dilts et al., 1996; Hyman et al., 2005). They also display difficulties on specific measures of calculations and applied problems (Cutting et al., 2000; Mazzocco et al., 1995). Levels of impairment and SLD in mathematics are often reported at similar rates or occasionally higher than those for reading and spelling. Hyman and colleagues (2006) reported the incidence of SLD (discrepancy definition) in mathematics to be 9.9%. Whereas De Winter at al. (1999) reported that 21.2% of

children scored in the severely impaired range (2 SD below the normative mean) on a measure of arithmetic, compared to 16.8% and 16.3% for spelling and reading

respectively. Krab et al (2008) reported similar rates (23%) using a slightly different criteria for LD in mathematics (normal IQ and performance 1 SD below mean). As previously mentioned Orraca-Castillo et al. (2014) reported that 18.8% of children assessed had dyscalculia, or a LD in mathematics. Finally there is some evidence to suggest that children with a LD in mathematics are at greater risk of LD in reading (Mazzocco, 2001; Orraca-Castillo et al., 2014), although this is an area that needs further exploration.

In summary, despite the variance in reported rates of LD/SLD it is clear that impairment in academic performance is one of the most common complications of NF1 in childhood (Lehtonen et al., 2013). Study findings indicate that children with NF1 are at increased risk of difficulties in all academic domains. In line with findings in the general population (Landerl & Moll, 2010; Rutter, Caspi, Fergusson, & et al., 2004), there is some evidence to suggest that males with NF1 are at increased risk of LD and also that children with a LD in one domain, are at greater risk of LD in other academic areas. To date, little is known about early signs of LD in young children with NF1. While Lorenzo et al (2010) reported that signs of language and cognitive impairments can be detected as early as 21 months in children with NF1 further research is needed to identify specific early markers of those children at risk for later learning difficulties.