Understanding Fragile X Syndrome: A Comprehensive Guide

1. Fragile X: A Family of Disorders Dianne M. McBrien, MD Clinical Associate Professor of Pediatrics University of Iowa Hospitals and Clinics

3. Sequence of bases codes for proteins • Proteins then facilitate or inhibit various reactions related to physiology • Change or abnormality in the sequence is called a mutation

4. Triplet repeat expansion mutation • Normal number of CGG repeats at site is less than 50 • Premutation consists of 55 to 200 repeats • The mutation consists of >200 repeats • Number of repeats can increase with generations

5. What is fragile X? • Family of genetic conditions • Mutations in what is now known as FMR1 gene, discovered 1991 • Xq27.3 • Involves unstable series of trinucleotide repeats

6. FMR1 status can be: • Normal (<45 repeats) • Grey zone allele (45-54 repeats) • Premutation (55-200 repeats) • Full mutation (>200 repeats) • When we talk about a patient with fragile X syndrome, we are generally referring to an individual with the full mutation. When we talk about a patient who is a carrier, we are referring to an individual with the premutation.

7. What makes the premutation expand to a full mutation in the next generation? • Female carrier • Number of repeats (more repeats, more unstable) • Association with AT base pairs

8. What makes the premutation expand to a full mutation in the next generation? • Female carrier • Number of repeats (more repeats, more unstable) • Association with AT base pairs

9. Full expansion of the gene induces methylation, which silences FMRP production • The cognitive and behavioral phenotype is attributed to the complete or partial loss of FMRP

10. What does FMRP do? • Binds mRNAs • Helps to transport them along the neuron to where they are needed • Inhibits translation of these templates until the right signal arrives • Helps in synaptic plasticity

11. What does FMRP do?

14. FXS: Problems associated with the full mutation • Cognitive deficits • Autistic-like features • Severe social anxiety • AD/HD • Behavioral problems • Sleep disruption

15. Other medical issues • Hypotonia • Seizures in at least 17% of males • Ear and sinus infections • Joint hypermobility • Flat feet • Mitral valve prolapse • PWS-like phenotype in some patients

16. Connective tissue dysplasia cont’d. • Hernias • Recurrent ear infections • Frequent sinusitis • Mitral valve prolapse • Unusually soft skin

17. Cognitive function • Range is quite wide • 50-60% within moderate to severe range of MR • Function of how methylated (silenced) FMR1 gene is as well as possible mosaicism • Characteristic neuropsychological profile

18. Strengths and weaknesses • Strong verbal labeling and comprehension—may understand more than rest of abilities would suggest • Strong at long-term memory and simultaneous processing • Weak at several measures of short-term memory and arithmetic • Executive function poor

19. Strengths and weaknesses • Strong verbal labeling and comprehension—may understand more than rest of abilities would suggest • Strong at long-term memory and simultaneous processing • Weak at several measures of short-term memory and arithmetic • Executive function poor

20. Autism in FXS • More problems with eye contact than children with autism and no FXS dx • More social relatedness • Extremely high degree of social anxiety

21. Speech and language • Poor articulation consistent with cognitive age • Rapid, dysrhythmic rate—”cluttering” • Self-repetitions (palilalia) c/w autistic individuals without FXS

22. Girls and women with FXS • Physical features are milder than in males, more common in patients with full mutation • Borderline or mild MR IQ, LD, attentional problems, impulsive behavior, poor eye contact in girls with FM

23. Characteristic appearance • May not be present in infants and young children • May develop over time • Absence of which cannot be used to rule out FXS

24. Premutation carriers • Mutation is between 55 and 200 repeats • Premutation carriers once thought to be asymptomatic

25. Fragile X tremor-ataxia syndrome (FXTAS) • Seen in 25-30% men > 50 years old who have the premutation • Limb and truncal ataxia, tremor, cognitive symptoms • Misdiagnosed as Parkinson’s disease

26. Premature ovarian insufficiency (POI) • 25% of women with premutation • Infertility • Reduced bone density • Irregular menses • Menopause prior to 40 years

27. Other problems associated with the premutation • ADHD, autism spectrum d/o, learning issues • Social anxiety, phobias, and depression • SLE, other autoimmune disease • Thyroid dysfunction • Hypertension • Chronic muscle pain syndrome

29. What’s going on? • FMRP mRNA in WBCs 2 to 8 times normal • High levels of FMRP mRNA in FXTAS inclusions • Not toxic in itself • Thought to induce a state of oxidative stress”heat shock” proteins

30. Targeted treatments: Promise, uncertainty

31. Animal models for fragile X

32. The mGlur5 theory • Activation of mGlur5LTD of synaptic responses • LTD much more pronounced in the KO mouse than in wild mouse (Huber et al, 2002) • Neuropsychiatric phenotype response to exaggerated mGlur5 response

33. Knockout mouse Wild type mouse

34. In the knockout mouse, mGlur5 blockers have shown: • correction of dendritic spinal abnormalities • correction of seizure threshold • improvement in several measures of learning

35. mGlur5 blockade: Human trials • Fenobam (Berry-Kravis et al, 2009): Improved communication, eye contact, PPI deficit • AFQ056: Response on ABC, CGI, as well as a measure of repetitive behaviors

36. mGlur5 antagonist clinical trials • R04917523 (FX trial in adults, now closed) • Same compound in children—the Foxtail study, still enrolling

37. Phase II study • Double blinded, randomized placebo trial • Three arms: 0.5 mg, 1 mg, and placebo • WISC-IV, ADOS, Vineland, Social Responsiveness Scale, ADOS, ABC, CGI-S and CGI-I, VAS, Vineland, RBANS, Caregiver Burden Inventory

38. The role of GABA • Lower levels of GABA-A receptors • Abnormally low GABA activity in amygdala • GABA-B agonists block glutamine release • Arbaclofen

39. Arbaclofen • Potent GABA-B agonist • Improvements in ABC social withdrawal score, Vineland Play and Leisure Scale, and Visual Analog Scale, as well as improvement on CGI • Well tolerated, with minimal side effects • Trial was discontinued abruptly

40. Lithium • Inhibits GSK3B, which is a kinase • Overactive in the KO mouse • Li normalizes its levels • Reverses a number of behavioral abnormalities in the KO mouse, along with dendritic spinal abnormality and seizure threshold

41. Human trials of lithium in FXS • 15 patients with FXS • Improvements in Total ABC score, Hyperactivity, Inappropriate Speech and Lethargy (Social Withdrawal) subscales • The Maladaptive Behavior subscore from the VABS • A parent visual analog scale for target behaviors • CGI scale • RBANS list learning task • Subgroup continued on Li for a year with persistent improvement on ABC-C and VABS • (Berry-Kravis et al. 2008)

42. Minocycline • Treatment of KO hippocampal cell culture improves dendritic spine maturity • Treatment of nursing KO dams improves hippocampal dendritic spine anatomy in pups • Reduced anxiety in exposed pups

43. Human trials of minocycline • Paribello et al: Positive effects in a group of boys 13 years and older • Currently a controlled trial going on at UC-Davis for children from 3.5 to 16 years

44. Center for Disabilities and Development University of Iowa Fragile X Clinic