All FOXP2-related speech and language disorders, regardless of the underlying genetic alteration, have a core phenotype: childhood apraxia of speech (CAS), a disorder of speech motor programming or planning that affects the production, sequencing, timing, and stress of sounds, syllables, and words. All individuals with CAS – whether caused by an alteration of FOXP2 or of an unknown cause – have difficulties in automatically and accurately sequencing speech sounds into syllables, syllables into words, and words into sentences with the correct prosody. Additional findings in FOXP2-related speech and language disorders can include oral motor dyspraxia (difficulty planning or programming oral movements on command); dysarthria (a neuromuscular-based speech disorder that may affect nasal resonance, voice quality, prosody, and breath support for speech); moderate to severe receptive and expressive language disorder; and reading and spelling impairments. The underlying genetic cause of FOXP2-related speech and language disorders is either disruption of FOXP2 only (referred to in this GeneReview as FOXP2-only-related speech and language disorder) or large copy number variants (i.e., contiguous gene deletions), structural variants (i.e., chromosome translocation or inversion), or maternal uniparental disomy of chromosome 7 (UPD7) involving FOXP2 (here referred to as FOXP2-plus-related speech and language disorders). The genetic alteration determines if only speech and language problems are present (FOXP2-only-related speech and language disorder) or if more global developmental and behavioral issues are likely to be present as well (FOXP2-plus-related speech and language disorder). In FOXP2-only-related disorders, nonverbal (performance) IQ is typically more preserved compared to verbal IQ. Fine motor skills may be impaired (e.g., buttoning clothes, tying shoelaces), yet gross motor skills are normal. Autistic features and dysmorphic findings have been reported in a few affected individuals. In FOXP2-plus-related disorders oral motor deficits, global developmental delay, and autism spectrum disorder are common.

Any autosomal recessive non-syndromic intellectual disability in which the cause of the disease is a mutation in the CC2D1A gene.

Optic atrophy-11 (OPA11) is an autosomal recessive disorder characterized by delayed psychomotor development, intellectual disability, ataxia, optic atrophy, and leukoencephalopathy on brain imaging. Laboratory studies are consistent with mitochondrial dysfunction (summary by Hartmann et al., 2016). For a discussion of genetic heterogeneity of optic atrophy, see OPA1 (165500).