From OMIM
Speech-language disorder-1 is an autosomal dominant disorder characterized by severe orofacial dyspraxia resulting in largely incomprehensible speech. Affected individuals were originally thought to have specific defects in the use of grammatical suffixation rules (Gopnik, 1990; Gopnik and Crago, 1991). The phenotype, however, is broader in nature, with virtually every aspect of grammar and language affected (Fisher et al., 1998). Vargha-Khadem et al. (1998) concluded that the disorder is characterized by abnormal development of several brain areas critical for both orofacial movements and sequential articulation, resulting in marked disruption of speech and expressive language. Relation to Specific Language Impairment Children who fail to develop expressive and/or receptive language normally, in the absence of explanatory factors such as neurologic disorders, hearing impairment, or lack of adequate opportunity, are clinically described as having specific language impairment (SLI; see 606711) (Bartlett et al., 2002). See also familial developmental dysphasia (600117).  http://www.omim.org/entry/602081

From MedlinePlus Genetics
FOXP2-related speech and language disorder is a condition that affects the development of speech and language starting in early childhood. Affected individuals have a speech problem known as apraxia, which makes it difficult to produce sequences of sounds, syllables, and words. This condition results from abnormalities involving parts of the brain that plan and coordinate movements of the lips, mouth, and tongue. Children with apraxia typically say their first words later than other children. Their speech is often difficult to understand, although the clarity of speech improves somewhat over time. Some affected individuals also cannot cough, sneeze, or clear their throats.

In addition to having problems with producing speech (expressive language), people with FOXP2-related speech and language disorder may have difficulty with understanding speech (receptive language). Some also have trouble with other language-related skills, such as reading, writing, spelling, and grammar. In some affected individuals, problems with speech and language are the only features of the condition. Others also have delayed development in other areas, including motor skills such as walking and tying shoelaces, and autism spectrum disorders, which are conditions characterized by impaired communication and social interaction.  https://medlineplus.gov/genetics/condition/foxp2-related-speech-and-language-disorder