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Genetic contributions to neurodevelopmental disorders
Published in Anna L. Barnett, Elisabeth L. Hill, Understanding Motor Behaviour in Developmental Coordination Disorder, 2019
Such clear inheritance patterns are rarely seen in conditions like DCD but are sometimes observed in rare and distinct forms of neurodevelopmental disorder. For example, in the 1990s, scientists described a family in which three generations were affected by severe developmental verbal dyspraxia (difficulty with speech but not with other aspects of motor control and coordination) inherited in a Mendelian dominant fashion (Hurst, Baraitser, Auger, Graham, & Norell, 1990). In such cases, gene mapping typically involves a search for variants that are shared by affected family members but not unaffected individuals. Luckily, the reported family was extensive and this approach led to the identification of a mutation in a gene known as FOXP2 (short for Forkhead-box-protein-P2) (Fisher, Vargha-Khadem, Watkins, Monaco, & Pembrey, 1998; Lai et al., 2000; Lai, Fisher, Hurst, Vargha-Khadem, & Monaco, 2001). The mutation only led to a small change in the protein coded by this gene (a non-synonymous mutation, as in Figure 5.1.iv.c) but this small change occurred in a critical region (Lai et al., 2001). The change obliterated the DNA-binding functionality of the protein. Subsequent studies have identified additional individuals with FOXP2 mutations, all of whom present with a disorder of motor control that restricts their speech production (Estruch, Graham, Chinnappa, Deriziotis, & Fisher, 2016; Morgan et al., 2015).
Speech and language assessment
Published in James Law, Alison Parkinson, Rashmin Tamhne, David Hall, Communication Difficulties in Childhood, 2017
Alison Parkinson, Suzanne Pate
Praxis is about the performance of an action, in this context an oro-motor or a verbal action. Speaking is an action which involves the temporal organisation and sequencing of speech sounds, and as such relies on a hierarchy of planning, execution and monitoring, from an ideational level through phonological, phonetic and motor programming levels to an articulatory level: a system which may break down at one or more levels. As with other groups of speech- and language-impaired children, the process of coming to a consensus about what constitutes verbal dyspraxia in terms of a set of symptoms or clusters of symptoms has been slow. Dyspraxia has variously been described as a motor programming deficit and a linguistic impairment, reflecting researchers’ diverse opinions about the primary level of breakdown. The field has been further complicated by the use of a range of terminology: Developmental Verbal Dyspraxia, Developmental Articulatory Dyspraxia, Developmental Apraxia of Speech and Immature Articulatory Praxis. Focusing on Developmental Verbal Dyspraxia, Ozanne14 describes it as a multideficit disorder with core deficits at the levels of phonological planning, phonetic programming and oro-motor and speech motor programme implementation. From a clinical perspective the key questions are about the level of severity and, related to this, the responsiveness to intervention. In terms of differential diagnosis it is also now becoming clear that the symptoms of dyspraxia merge at the margins with both those of dyslexia and phonological disorder.
Candidate gene variant effects on language disorders in Robinson Crusoe Island
Published in Annals of Human Biology, 2019
Hayley S. Mountford, Pía Villanueva, María Angélica Fernández, Zulema De Barbieri, Jean-Baptiste Cazier, Dianne F. Newbury
Despite the remarkably high prevalence of DLDs, little is understood of the underlying aetiology. It is well established that DLD has a strong familial component, supported by twin and heritability studies (Stromswold 1998; Bishop et al. 2006; Barry et al. 2007). These familial disorders, termed Mendelian disorders, result from inheriting either one (dominant) or two (recessive) copies of extremely rare and damaging variants, which act to disrupt protein function. The most well-known and clear-cut examples of Mendelian inheritance in language disorders can be found in a motor disorder known as childhood apraxia of speech (CAS), also known as developmental verbal dyspraxia. CAS is considered to be a sub-category of DLD that specifically refers to difficulties in the fine motor control required to produce and coordinate sounds into complete words and sentences, characterised by difficulties in producing speech sounds, dysarthric speech and poor oral motor control. The first CAS case to be solved involving a dominant mutation in the gene FOXP2 was found to be shared by all CAS-affected members of a large multigenerational pedigree, known as the KE family (Lai et al. 2001). The p.Arg553His FOXP2 mutation is fully-penetrant in the KE family, meaning that all carriers have CAS and non-carriers do not. A number of subsequent studies have identified additional FOXP2 mutations in other unrelated individuals as the cause of CAS (MacDermot et al. 2005; Tomblin et al. 2009; Turner et al. 2013; Moralli et al. 2015; Liegeois et al. 2016; Reuter et al. 2017), providing further evidence of the gene’s role in language. A small number of other genes have also been implicated in the CAS phenotype. One such gene is the protein transporter ERC1 (Thevenon et al. 2013), which was identified by overlapping 12p13.33 deletions in five unrelated CAS cases.