FOXP2 presentation

Identification of FOXP2 Truncation as a Novel Cause of Developmental Speech and Language Deficits: 

Identification of FOXP2 Truncation as a Novel Cause of Development al Speech and Language Deficits Brett Gellman Melissa Yeung November 6, 2007

What is the FOXP2 gene?: 

What is the FOXP2 gene? The first gene to be connected to a developmental communication disorder Encodes a transcription factor Contains polyglutamine tracts, a zinc finger, a leucine zipper motif, and a forkhead-box DNA-binding domain Likely to regulate gene expression in defined areas of developing lung, cardiovascular, intestinal, and neural tissue Red segment represents the location of the mutation

Developmental verbal dyspraxia: 

Developmental verbal dyspraxia Difficulties controlling the speech organs. Difficulties making speech sounds Difficulty sequencing sounds Within a word Forming words into sentences Difficulty controlling breathing and phonation. Slow language development. Difficulty with feeding Infected individuals express linguistic or phonological impairment. Key aspects include:

Developmental verbal dyspraxia: 

Developmental verbal dyspraxia The problem occurs when the brain tries to tell the muscles what to do -- somehow that message gets scrambled. It's like trying to watch cable t.v. stations without the right descrambler. There is nothing wrong with the t.v. station, and nothing wrong with your set. It's just that your set can't read the signal that the station is sending out. The child's language-learning task is to figure out how to somehow unscramble the mixed message their brain is sending to their muscles.

Previous Research: 

Previous Research The KE Family Studied to try to find the gene responsible for language production Out of 37 family members distributed across 3 generations, 15 suffered from some form of specific language impairment High amount of affected individuals within the same family indicates: The disorder might be attributed to a single gene transmitted by either parent The gene follows a dominant/recessive pattern and is not sex-linked.

Hypothesis: 

Hypothesis “… we might maximize the possibility of detecting further etiological variants by screening, for the first time, a panel of patients with a primary diagnosis of verbal dyspraxia.” No previous study has preformed this mutation screening. Previous screening studies of FOXP2 have focused on individuals with typical specific language impairment (SLI), autism, or dyslexia. “…the most overt symptom of their disorder is a severe developmental verbal dyspraxia… the most reliable indicator of affection status…”

The Experiment: 

The Experiment Wanted to choose patients that most matched the phenotype of the KE family Patients were selected for FOXP2 screening if they had: Presence of clinically diagnosed speech articulations problems Normal karyotype Absence of mental retardation and congenial abnormalities Normal hearing No other medical/genetic diagnosis DNA samples collected from 49 probands (the first affected family member with a genetic disorder) of whom 10 had at least one affected sibling All individuals were white, aged 4-12 (except for siblings 30 and 33) and lived in Europe, Australia, or the US

The Experiment: 

The Experiment Conducted mutation screening across all FOXP2 exons identified by Lai et. al. (2001) Used protocols and primers outlined by Newbury et. al. (2002)

Slide9: 

5’ UTR regions Alt. spliced Predicted to be non-coding Alt. spliced Coding yields aa insertion Polyglutamate tracts Zinc finger Leucine zipper Forkhead domain

R328X Mutation: 

R328X Mutation C  T transition in exon 7 Heterozygous nonsense mutation that leads to a stop codon Leads to truncated product yielding FOXP2 protein lacking: Zinc finger Leucine zipper Forkhead DNA binding domain

R553H Mutation: 

R553H Mutation Heterozygous missense mutation Arginine-to-histidine substitution Highly conserved Causes deficits in orofacial movements required for speech (verbal dyspraxia) and a wide range of linguistic and grammatical problems

More Mutations: 

More Mutations Two coding changes: A T transversion in exon 2 Insertion of CAGCAGCAACAA into polyglutamine-encoding region of exon 5 Changes yield Glutamine-to-leucine change Polyglutamine-tract expansion from 40-44 consecutive glutamines In each case, the proband had a sibling who was diagnosed but did not carry the relevant coding change.

de novo balanced Translocation: 

de novo balanced Translocation Chromosomes break and do not join back together where they originally broke People with balanced translocation are “carriers” and no pheneotype is expressed until their offspring Involves chromosomes 7 and 5 on the FOXP2 locus Normal Balanced translocation

Griffiths Mental Development Scale (1970): 

Griffiths Mental Development Scale (1970) Assesses the development of a child from birth to 8 years of age Evaluates 6 domains: Locomotor Personal and social Hearing and speech Eye-hand coordination Performance Practical reasoning

Preschool Language Scale (1992): 

Preschool Language Scale (1992) Formally measures receptive and expressive language skills Assessments indicate developmental delays in the domains of speech and language, and social skills

Case Study: 

Case Study Individual is 4 years old Communicated mainly using single words Unable to repeat multisyllabic words Had difficulties with practical reasoning activities Language skills were almost 3 standard deviations below the normal mean Younger sister At 1 yr 8 mo, showed poorest performance in hearing and speech Did not speak any words and could not identify objects General motor skills appeared normal Mother Carried R328X mutation Poor speech clarity and very simple grammatical constructions

Conclusion 1: R328X: 

Conclusion 1: R328X Nonsense mutation the yields a truncated FOXP2 protein lacking key functional domains This is the first report of a point mutation in FOXP2 since the identification of the KE mutation

Conclusion 2: Verbal Dyspraxia: 

Conclusion 2: Verbal Dyspraxia Developmental verbal dyspraxia yields a high frequency of protein mutations Limited sample pool to individuals that did not express SLI or autism It is appropriate to re-evaluate FOXP2’s role in neurodevelopmental disorders

Conclusion 3: Screening Small Coding Regions: 

Conclusion 3: Screening Small Coding Regions Data cautions against only looking at limited coding regions of FOXP2 Can affect areas which lie further from functional domains but still can have major consequences for protein function

Conclusion 4: Truncation: 

Conclusion 4: Truncation Heterozygous nonsense mutation causes truncation of FOXP2 Leads to hypothesis that FOXP2-related disorders may result from this truncation mechanism

Final Conclusion: 

Final Conclusion Presence of verbal dyspraxia is a key clinical aspect linked to children likely to have mutations in FOXP2 Individuals with R328X can now be assessed using neuropsychological tests like those used on the KE family This research “opens the door for the future integration of behavorial and neurological data from patients with different allelic variants of FOXP2”

Discussion: 

Discussion Do you think that this study is significant to the results from the KE family? Why do you think no other previous study has performed this mutation screening on children with a primary diagnosis of verbal dyspraxia? Instead of just looking at individuals with no other learning disabilities (i.e. autism, SLI) , should they have looked at FOXP2’s affect on these? Do you think the conclusions were effective? Should the researchers have done more?