Dyslexia or reading disability is a neurodevelopmental condition with a relatively high prevalence in the population (5 - 10% depending on diagnostic criteria). Typically, reading assessment and diagnosis is focused on children, who are categorized as dyslexic if they have reading difficulties that cannot be explained by other factors such as low IQ or other neurological disorders. Although dyslexia can become milder in adulthood, people often retain lifelong difficulties with reading that may affect training, employment and life choices. Dyslexia usually has a complex and multifactorial background that includes genetic contributions. Some unusual families may have relatively rare forms of the disorder that are caused by single genetic mutations with strong effects on reading ability. Here we have focused on extended families with multiple affected members, which may have these kinds of genetic subforms of the disorder. Word and nonword reading fluency measures have been taken for all family members available. We have evaluated these continuous traits across the generations in order to best discriminate affected from unaffected members. We also propose a genetic strategy focused on sequencing the genomes of key members in order to identify possible risk variants. Genes that are found through this approach may be particularly crucial for the development of normal reading and language skills.