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Rett Syndrome. Presentation by: PHM142: Nov. 16, 2012 Brian Talan Chia Hui Chung Hardit Khuman Priya Patel . PHM142 Fall 2012 Coordinator: Dr. Jeffrey Henderson Instructor: Dr. David Hampson. Overview:.

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rett syndrome

Rett Syndrome

Presentation by: PHM142: Nov. 16, 2012

Brian Talan

Chia Hui Chung

Hardit Khuman

Priya Patel

PHM142 Fall 2012

Coordinator: Dr. Jeffrey Henderson

Instructor: Dr. David Hampson

overview
Overview:
  • What is Rett syndrome?
  • Symptoms & associated effects
  • Biochemical mechanism
  • Diagnosis & available treatments
what is rett syndrome
What is Rett Syndrome?
  • A neurodevelopment disorder: autism spectrum disorder
  • Associated with mitochondrial abnormalities in muscles and the brain
  • Predominantly affects females
  • Prevalence: 10 000 to 15 000 live female births
  • Characterized by normal growth and development followed by a slowing of development
  • Main effect: loss of motor and intellectual abilities
what causes rett syndrome
What causes Rett Syndrome?
  • Caused by a mutation of the MECP2 gene on the X chromosome
  • Severity of the syndrome is partly a function of how many cells express the normal MECP2 gene
  • Males with MECP2 defect have no protection from the harmful effects of Rett’s syndrome
symptoms
Symptoms:
  • Slowed brain growth resulting in microcephaly
  • Abnormal hand movements
  • Loss of speech
  • Difficulty breathing due to intermittent hyperventilation
  • Seizures
  • Autism
four stages of rett sydrome

Stage I

    • 6-18 months
    • Subtle symptoms, including lack of eye contact
  • Stage II
    • 1-4 years
    • Loss of speech and hand movements, difficulty breathing
  • Stage III
    • 2-10 years
    • Problems with move movement continue, but see improvements in behaviour
  • Stage IV
    • 10-50 years
    • Reduced mobility
Four stages of Rett Sydrome:
the nuts and bolts mechanism
The nuts and bolts: mechanism
  • Epigenetics:
  • Genetic control by factors other than the DNA sequence of the gene being controlled (via silencing mechanisms – DNA methylation, histone modification, RNA-associated silencing, X inactivation– or activating mechanisms)
  • Turning on and off sets of genes vital in cell differentiation and therefore human development and normal function
  • Here, we will see the epigenetic effects of one such factor, MeCP2, a protein whose gene mutation is heavily associated with Rett Syndrome

(Simmons, 2008 adapted from Egger, 2004)

mecp2 gene
MECP2 Gene:
  • Methyl-CpG binding protein 2 gene (MECP2)
  • 1999: MECP2 Mutation female patients with Rett Syndrome discovered
  • 90 - 95% of girls with RS have this mutation; diagnosis remains a clinical matter
  • Located on q28 on the human X chromosome
  • MeCP2 protein expressed highest in neurons, specifically postmitotic neurons
    • deficiency in neurons has been shown to be sufficient in causing Rett Syndrome like phenotypes in mouse; other studies imply that the various Rett Syndrome phenotypes are a result of MeCP2 deficiency in specific neuron populations as well as with glia, though exact mechanisms that lead to Rett Syndrome unknown
  • XCI (X Inactivation) has been demonstrated for the MECP2 gene in mice and humans
    • leads to variability in severity of syndrome features exhibited by those with the mutation
slide10

(Weaving et al, 2005)

Figure A. MECP2 gene structure, showing the alternative splicing patterns that yield the A and B isoform of the MeCP2 protein

The A splicing variant includes part of exon 2 but not exon 1, and translates to the MeCP2A (or β) isoform, of 486 amino acids

The B splicing variant includes exon 1 but not exon 2, and translates to the MeCP2B (or α) isoform, of 498 amino acids

MeCP2B is the predominant isoform in the brain, whose amino acid sequence structure is shown in Figure B.

MBD: Methyl-CpG binding domain, NLS: Nuclear Localization Signal, TRD: Transcription Repression Domain, WW domain binding region: group II WW binding domain ( specific binding to WW domains of splicing factors (e.g. formin binding protein II, and HYPC (Huntington yeast protein C)

slide11

(Zachariah and Rastegar, 2012)

MECP2B is now called MECP2E1; MECP2A is now called MECP2E2

slide12

Exact effects of MECP2 mutation to cause Rett Syndrome unknown

  • Studies continue to elucidate the targets of MeCP2
  • MECP2’s high expression in normal, mature neurons (continues to adulthood) implies importance in function

(Zachariah and Rastegar, 2012)

slide13

MeCP2 originally thought to act globally in the repression of transcription

  • studies suggest that it has roles in regulating expression of genes in active neurons as suggested here for Bdnf in mouse and rat, and Hairy2a in Xenophus

(Weaving et al, 2005)

slide14

mSin3 and

Histone Deacetylase co-repressors

Dlx5 and Dlx6 exhibited 2x expression in MeCP2-null mice brains

(Zachariah and Rastegar, 2012)

other possible causes of rett syndrome and avenues of research
Other possible causes of Rett Syndrome and avenues of research:
  • CDKL5 (Cyclin Dependent Kinase-like 5) - mutations identified in patients with atypical Rett Syndrome, the early-onset seizure variant; exact mechanisms and relation with MECP2 unknown
  • Mutations in FOXG1 suggested to cause the congenital variant
  • Studies are looking into Klinefelter Syndrome (XXY) in males with Rett Syndrome as well as mosaicism and it’s impacts on the features of the syndrome exhibited
treatments
Treatments:
  • No cure
  • L-carnitine (lipid peroxidation/oxidative stress)
  • Dietary: red meat, milk, eggs
  • Bromocriptine and L-dopa
  • Induced pluripotent stem cells
  • Carbamazepine used to treat seizures
diagnosis support
Diagnosis & Support:
  • Genetic testing to look for the gene defect
  • Mostly diagnosed by proliferation of associated symptoms

Support:

  • Ontario Rett Syndrome Association
  • Many on-line support groups for parents
summary

Rett Syndrome caused by a mutation of MECP2 gene on the X chromosome

  • Symptoms include neurological and motor deficits such as abnormal hand movements, loss of speech, seizures, and autism
  • Symptoms can be divide into four general stages which outline the life span of an individual with Rett Syndrome
  • Mutation in the MECP2 is found 90-95% of Rett syndrome patients
  • MECP2 to E1 isoform shows importance in neuron function
  • Exact mechanism still unknown and currently being studied
  • Common treatments include: L-carnitine, bromocriptine, L-dopa, carbamazepine and pluripotent stem cells
Summary:
references

"Rett Syndrome Fact Sheet." Ninds.nih.gov. Office of Communications and Public Liaison National Institute of Neurological Disorders and Stroke, Nov. 2009. Web. 15 Nov. 2012. <http://www.ninds.nih.gov/disorders/rett/detail_rett.htm>.

"Rett Syndrome." Nichd.nih.gov. Eunice Kennedy Shriver National Institute of Child Health and Human Development, 8 Feb. 2010. Web. 15 Nov. 2012. <http://www.nichd.nih.gov/health/topics/rett_syndrome.cfm>.

Amir, R.E., et. al. “Rett syndrome is caused by mutations in X-linked MECP2, encoding methyl-CpG-binding protein 2”. Nature Genetics 23.1 (1999): 185-188.

Glaze, D. G. "Neurophysiology of Rett Syndrome." Journal of Child Neurology 20.8 (2005): 740-46.

Hagberg, Bengt. "Clinical Manifestations and Stages of Rett Syndrome." Mental Retardation and Developmental Disabilities Research Reviews 8.2 (2002): 61-65.

Plioplys, Audrius V., and Irene Kasnicka. "L-Carnitine as a Treatment for Rett Syndrome."Southern Medical Journal 86.12 (1993): 1411-413.

Michele, Zappella, Genazzani Andrea, Facchinetti Fabio, and Hayek Giuseppe. "Bromocriptine in the rett syndrome."Brain and Development 12.2 (1990): 221-25.

Kliegman, Robert. Nelson Textbook of Pediatrics. Philadelphia (Pa.): Elsevier Saunders, 2007.

References:
slide20

Simmons, Danielle. “Epigenetic Influences and Disease”. Nature Education 1.1 (2008).

Zachariah, Robby Mathew and Rastegar, Mojgan. “Linking Epigenetics to Human Disease and Rett Syndrome: The Emerging Novel and Challenging Concepts in MeCP2 Research.” Neural Plasticity 2012. 415825 (2012): 1-10.

Weaving, L S, Ellaway ,C J, Gécz, J, and Christodoulou, J. “ Rett Syndrome: clinical review and genetic update”. Journal of Medical Genetics 42.1 (2005): 1-7.

“Rett Syndrome”. Genetics Home Reference. US National Library of Medicine, 12 November 2012.

“Rett Syndrome”. Eunice Kennedy Shriver National Institute of Child Health and Human Development 06-5590 (April 2006).