Rather than being separate and distinct, learning disabilities are often comorbid in children, suggesting that there may be overlaps in deficits and etiologies. Through the identification of genes influencing processes that are important to learning, new developments in genetic analysis may help define alternate ways of conceptualizing different types of learning disabilities based on the genes and endophenotypes that are involved in each one. There has been evidence since the turn of the last century that reading disability (RD) occurs in families, and twin studies have shown heritabilities around 0.56. Although the definitions of RD and language impairment (LI) are based on measures that are very different, the disorders share some similarities; the heritabilities for deficits are similar, males are affected more often than females, and young children with LI are at greater risk for RD. Molecular genetic studies support common genetic influences on RD and speech sound disorder (SSD).