The Importance of Family History in Dyslexia

Present research shows that having a biological family member with developmental dyslexia, in particular immediate family members like parents, is a risk factor for dyslexia. Family history of developmental dyslexia is important to consider given its status as an early risk factor, as the presence of family history can be determined before a child begins to learn to read. We briefly summarize findings related to family history in developmental dyslexia and discuss the potential of using family history questionnaires to predict reading outcomes and to supplement assessments. Family history questionnaires have the potential to enhance early screening for dyslexia risk. These questionnaires may be an invaluable tool for teachers, allowing them to engage in proactive monitoring, referral, and early identification of impaired literacy risk in school-aged children.

Developmental dyslexia (a.k.a., word-level reading disorder, specific reading disability, or simply dyslexia) is a specific learning disability that is neurobiological in origin. It is marked by difficulties in accurate and/or fluent word reading despite intact intelligence, which is typically measured by IQ tests. Phonological skills range from basic abilities such as rhyme perception and syllabication to phonemic awareness. Deficits in these skills are one of the most common aspects of dyslexia. However, in recent years it has become clear that phonological deficits are not universal among children with dyslexia and may not always co-occur with word-reading deficits (Catts et al., 2017). Those with dyslexia may also have deficits in other areas, such as letter knowledge, rapid automatized naming (RAN), and oral language skills, with or without accompanying phonological deficits (Melby-Lervåg et al., 2012).

A large portion of these children can improve their reading ability with explicit, systematic, and evidence-based reading interventions (Peck et al., 2018). In order to improve children’s outcomes using these interventions, children must first be identified as having impaired reading ability. They are often required to be officially identified as having dyslexia in order to qualify for services. The process of getting this identification can take a great deal of time and resources for both the school and parents. We therefore subscribe to the view that it is important to consider whether there is a history of dyslexia or reading failure in biological family members as a first step towards early intervention. This type of screening can be done before children have begun reading instruction or are screened for word-level reading or even phonological skills. It may therefore provide important background information that can in turn inform reading instruction and practice very early on. Children who have a parent or sibling with dyslexia are said to have a family history of dyslexia and are considered at-risk students because of this predisposition. In this review, we discuss the effects of family history on the likelihood of later dyslexia identification and on reading-related skills both before and after children become literate. We propose that measures quantifying family history may have practical implications for identifying children who are at risk.

Family History in Predicting the Chances of Developing Dyslexia

Dyslexia tends to run in families, in part due to genes that are inherited, and in part due to shared environments between family members who live in the same home (Lefly & Pennington, 2000). Certainly, environment impacts reading to an extent, as enriched home literacy environments have been shown to have a positive impact on reading outcomes (Hamilton et al., 2016). However, research has also shown that there is a definitive genetic component to dyslexia (Peterson & Pennington, 2015). Studies focused on understanding how genes are related to reading reveal that there are many genes associated with reading, but each gene only contributes to a small fraction of the overall effect (van Bergen et al., 2014).

Children with a family history of dyslexia are more likely to have dyslexia themselves. An estimate derived from a wide range of studies which examined children at familial risk for dyslexia suggests that 34–54% of children with family history eventually show characteristics of dyslexia (Snowling & Melby-Lervåg, 2016). This estimate describes a range for the average prevalence of several populations with risk for developing dyslexia. The range is based on slight differences in how individual researchers classify dyslexia across the studies included, which numbered over a dozen. The same paper found that children without a family history develop symptoms of dyslexia at a rate of 8–16% (Figure 1).

Figure 1.

Blue and red circles show the relative proportion of those with and without RD family history (FH) in the total population (without: blue, FH−; with: red, FH+). Green and orange circles show the rates of RD diagnosis within FH− and FH+, respectively, with FH+ children at greater risk compared to FH− children. Blue stick figures are FH−, and green stick figures are those who are FH− and have RD (8–16%). Red figures are FH+, and orange figures are both FH+ and have RD (34–54%). Rates come from the meta-analysis done by Snowling and Melby-Lervåg (2016).

Beyond just knowing if there is a family history of dyslexia, recent research has suggested that it is useful to know how many family members have a family history. Children of two parents who both have self-reported reading difficulties show poorer reading-related skills than those with only one or no parent with difficulties. The largest differences in these skills, such as letter knowledge and phonemic awareness, are found between children whose parents are both impaired as compared to children whose parents both have typical reading skills (Esmaeeli et al., 2018). In other words, children of two parents who both have a history of dyslexia are likely to be more severely impaired than those who have no or only one affected parent.

In summary, researchers have found that those with biologically closer family members (e.g., identical twins rather than regular siblings) and more family members (e.g., both parents rather than just one) who are diagnosed with dyslexia are themselves more likely to have dyslexia and/or more severe impairment (Astrom et al., 2011; Schumacher et al., 2007). These results demonstrate the importance of gathering family history information to identify which children are more likely to be at risk for later developing dyslexia or impaired reading skills. If detailed family history information can be collected via in-depth self-report measures and is shown to be a reliable predictor of preliterate children’s later reading ability, these measures may be used in schools to assess children’s risk before they start to struggle; however, it is important to mention that family history on its own is not a substitute for clinical assessment or a comprehensive picture of a child’s risk.

Family History May Predict Preliterate and Postliterate Reading-Related Skills

Family history can also be a valuable tool for predicting the full range of reading-related skills rather than simple binary outcomes of dyslexic versus non-dyslexic. Evidence from behavioral and neuroimaging studies show that preliterate children with family history of dyslexia have weaker performance in speech, oral language, RAN and letter knowledge tasks, and in phonological skills related to the knowledge and manipulation of speech sounds. Furthermore, parental literacy predicts and explains much of the individual performance in reading and spelling ability, as well as reading fluency at younger ages (Snowling & Melby-Lervåg, 2016; Carroll et al., 2014). Additionally, in those with family history, there is reduced neural activity during reading-related tasks, as well as structural differences in the brain similar to those found in people with dyslexia (Vandermosten et al., 2016).

In young children, considering family history allows us to predict eventual reading ability later in life beyond what we can predict using only children’s current skills. For example, one study has shown that children’s vocabulary in the first 2 years of life predicted reading accuracy and reading comprehension a few years later. Interestingly, when family history was also taken into account, the researchers were able to better predict the children’s reading accuracy and reading comprehension (Duff et al., 2015, see Figure 2). In another study in 5-year-old children, family history predicted spelling outcomes 6 months later, at age 6, and reading accuracy 3 years later, at age 8, above and beyond predictions made using only baseline reading and language abilities at age 5 (Carroll et al., 2014).

Figure 2.

Illustration of how much more family history (FH) predicts reading abilities at ages 4–9 when added to behavioral measures at ages 1–2 (Duff et al., 2015).

This data suggests that gathering family history information very early on will allow us to identify which children are likely to later struggle in reading even before formal assessments are done in school. The effect of family history for predicting children’s reading seems to be particularly strong during early reading development (Conlon et al., 2006; van Setten et al., 2018). We believe this lends further support to the idea of including family history assessments in preliterate classroom settings to identify a child’s risk of struggling to learn to read. Information regarding family history may also be useful in cases when a child who is flagged as at risk does not later meet formal criteria for dyslexia. This is because these children may still have lower performance in RAN, letter knowledge, word decoding and/or phonological skills conferred to them by their parents with a history of dyslexia. They may therefore benefit from similar interventions.

A recent paper by Ferrer et al. (2021) explicitly discourages the practice of using family history as a screener for dyslexia. The authors state that family history on its own is inaccurate as a screening tool for identifying children as dyslexic. We agree that family history should not be used as a proxy for the identification of dyslexia. Rather, we want to make clear that the value of family history lies in its ability, in conjunction with other information, to help determine which children are at risk for reading difficulties. We also acknowledge that this means some of the children identified as being at risk may not be identified with dyslexia later. Moreover, we acknowledge that family history does not identify all children who will develop dyslexia, since not all children who are eventually identified have family history. Family history is therefore not a replacement for evidence-based early screening measures, especially when preliterate or literate children are old enough to be accurately assessed. Rather it can be used to identify preliterate children who are at-risk due to family history, but who are not yet old enough to be formally assessed.

Assessing Family History

Despite the promising role of family history for the early identification of dyslexia risk and for assessing severity of subsequent reading impairment, determining whether parents and other family members have dyslexia is often a challenge. Relatives may not have had access to high-quality instruction, resided in a location without the appropriate support structure in place, and/or grown up in a family without the knowledge or financial means to receive a formal assessment. Several adult self-report questionnaires have been developed and validated over the past few decades, primarily for research purposes. They are used as screening measures for learning difficulties, including reading difficulties. These questionnaires may be helpful in identifying family history in the absence of a documented history of dyslexia. In the next section, we briefly explain their applications and introduce a shortened version of one of the most well-known questionnaires that can detect dyslexia with high accuracy in parents.

First, it is helpful to understand the way family history data is collected and the kinds of questions which may be asked on family history questionnaires. Some current questionnaires use a self-rating scale for various listed dyslexia symptoms and patterns of behavior, such as how often an individual finds it difficult to read novel words and how often they engage in reading for leisure. A few questions may inquire specifically about a potential dyslexia diagnosis. For details, please see the Adult Reading Questionnaire (ARQ) in Appendix A of Snowling et al. (2012). In summary, the collection of family history data relies on self-reported symptoms, prompted by questions which are designed to elicit information on reading behavior and ability.

The 23(+3)-item Adult Reading History Questionnaire (ARHQ) is perhaps the most used questionnaire to identify the likelihood that an adult was a poor reader or had dyslexia in childhood. For detailed information on the ARHQ, see the Appendix in Lefly and Pennington (2000), or the page “Dyslexia Screener for Adults” on the International Dyslexia Association (IDA) website (https://dyslexiaida.org/screening-for-dyslexia/dyslexia-screener-for-adults/). The ARHQ is sensitive to the range of individual variation in reading ability, allowing the respondent to indicate their degree of difficulty with a particular skill, such as spelling and memory, as well as their general attitudes towards reading. However, while the full ARHQ is successful 75.9% of the time at identifying those with dyslexia, it has been reported as having only a 48.1% success rate for identifying non-dyslexic individuals. This means many who are flagged by the ARHQ as poor readers may actually be good readers, which indicates a high false positive rate. Therefore, while the ARHQ shows promise in identifying those who would benefit from intervention, it may overidentify “poor readers” who are actually good readers. Teachers need a more reliable screener so that schools do not have to provide intensive and unnecessary intervention to those who do not need it.

A recently developed shorter version of the ARHQ, called the ARHQ-Brief, consists of only 6 out of 23 items from the original ARHQ. It has been shown to correctly identify positive cases of dyslexia in adults 72.4% of the time and negative cases 81.5% of the time (Feng et al., 2021). The 6-item questionnaire and instructions for Feng et al. (2021) have been made publicly available on the article’s website and can be found at: https://journals.sagepub.com/doi/suppl/10.1177/00222194211047631/suppl_file/sj-pdf-2-ldx-10.1177_00222194211047631.pdf. Parental scores from both the full ARHQ and the revised ARHQ-Brief show a strong negative relationship with scores from diagnostic reading assessments in both adults and their children, indicating that those with a history of more severely impaired reading (i.e., higher ARHQ scores) indeed demonstrated lower reading performance, as did their children. More work is needed to scientifically test the ARHQ-Brief scale before it should be used in schools, but in the meantime the 6-item ARHQ-Brief shows promise in identifying children’s risk on the basis of family history.

Another advantage of the ARHQ is that it may identify parents who were never properly diagnosed with reading difficulties as children, but who have resolved their reading deficits by adulthood; hence it is difficult to identify whether they ever had dyslexia. In one study, a revised version of the ARHQ was used to investigate differences between three groups. Distinctions in reading and phonological skills were found between college-aged adults who (a) reported having a history of reading difficulties as children using the revised ARHQ but reported no reading impairment as adults (self-report group); (b) those who had no history according to the revised ARHQ and had no reading impairment as adults (control group); and (c) those who were formally diagnosed with dyslexia. The self-report group performed worse than the control group but similarly to the dyslexic group on tests of word identification, reading efficiency, and phonological skills (Deacon et al., 2012). This suggests that the ARHQ used in this study may identify adults who have compensated for their reading deficits but could still pass reading and/or phonological deficits on to their children. One drawback of the parental questionnaires is that they have not traditionally been used as a measure of family history in the empirical studies reviewed here, which tend to use actual parental reading scores rather than relying on self-report information. Therefore, the true relationship between parents’ self-reported reading abilities and their children’s outcomes is less well-studied despite showing promising results as described in Feng et al. (2021), and for this reason requires additional study.

Conclusions and Future Directions

There is a strong research foundation for the conclusion that the presence of family history significantly affects a child’s likelihood of developing reading difficulties. A self-reported family history questionnaire for reading may be useful to get a sense of whether adults have a history of dyslexia and whether a child is therefore at risk. In addition, it may serve as an early screener for dyslexia risk which can qualify children for early intervention in the development of pre-literacy skills when reading assessments are not usable—for instance, when a child is too young to assess their reading, or prior history is suspected in a parent but was never diagnosed. Policymakers are now recognizing the value of utilizing family history measures in early screening, and some states in the U.S. are beginning to include family history as an additional component of universal screening measures for students who are flagged as at risk: for country-wide and individual state policies on early screening and intervention, see the “State of Dyslexia” page on the National Center on Improving Literacy website (https://improvingliteracy.org/state-of-dyslexia). The brief 6-item version of the ARHQ has been shown to be highly accurate for identification of family history and predictive of children’s later reading performance. Introducing these tools in schools and clinical settings to screen for children who are too young to be identified as being at risk for or having dyslexia using standardized assessments is an important next step. This will allow us to determine whether their common use may positively impact outcomes for children with phonological impairment who are not yet eligible for intensive intervention.