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Duplications of the MECP2 gene region and severe mental retardation in males All Wales Molecular Genetics Laboratory All Wales Molecular Genetics Laboratory Classical Rett syndrome • X-dominant condition • (Originally thought to be) Lethal in hemizygous males • MECP2 mutations in males – Aneuploidy of X chromosome, mosaics for MECP2 mutations – Lethal neonatal encephalopathy born to asymptomatic or mildly affected carrier mothers with mutations that usually cause the Rett phenotype in females – MECP2 mutations that cause a milder Rett phenotype in females, and classic or atypical Rett in males – Milder male cases with MECP2 mutations that do not result in classical Rett in female carriers (XLMR) All Wales Molecular Genetics Laboratory Gene dossier: Expanding the testing criteria Minimum criteria required for testing to be appropriate as stated in the Gene Dossier: Criteria Tick if this patient meets criteria X-linked or sporadic inheritance Females Normal development for first 6-18 months followed by period of regression Deceleration in head growth Mental retardation Loss of purposeful hand use, repetitive stereotypic hand movements Males Neonatal encephalopathy All Wales Molecular Genetics Laboratory Gene map of duplicated region > 60 duplications (0.2Mb – large dups;Xq28-ter) All Wales Molecular Genetics Laboratory Duplication pathogenicity • Phenotypic severity does not correlate with duplication size (flanking genes could play a role) – LICAM (spastic paraplegia) • Critical region – MECP2 & IRAK1 • Gene dosage influences phenotype (triplication – more severe) – Transgenic mice over-expressing Mecp2: Normal at birth but develop Rett-like progressive neurologic problems and die prematurely • Female carriers are asymptomatic if skewing is favourable • ?Due to LCRs All Wales Molecular Genetics Laboratory Cardiff samples • 25 male samples now tested by MLPA • 12 rearrangements detected in 4 families All Wales Molecular Genetics Laboratory Cardiff case 1: aCGH partial dup RP1-29A6 (unconfirmed) FMR-1 (unconfirmed) MECP2 (confirmed by MLPA, partial dup exon 4 only) All Wales Molecular Genetics Laboratory Cardiff case 2: MLPA dup All Wales Molecular Genetics Laboratory Cardiff case 3: MLPA dup / triplication All Wales Molecular Genetics Laboratory Phenotype – Genotype correlation Case Genotype Phenotype 1 (aCGH, MLPA) Dup MECP2 exon 4 – SLC6A8 +dup FMR-1 (unconfirmed) +dupRP1-29A6 (unconfirmed) Severe MR, delayed motor development, behaviour problems, overeating, micropenis N.B. phenotype may be due to additional duplicated regions on X chromosome and not to partial duplication of MECP2 2 (MLPA) Dup MECP2 – L1CAM Severe XLMR, seizures & flapping hands, recurrent infections 3 (MLPA) Dup MECP2 ex 1-2 Trip MECP2 ex 3-4, IRAK1 Dup L1CAM – SLC6A8 Severe MR, immobile, recurrent infections, seizures, severe hypotonia 4 (MLPA) Trip MECP2 ex1-(5’)4 Dup MECP2 ex(3’)4 – SLC6A8 Severe MR, floppy, recurrent infections All Wales Molecular Genetics Laboratory Phenotype of “duplicated” males • • • • • Severe MR Initial hypotonia (floppiness) Progressive spasticity Recurrent infections (linked to IRAK1?) Absent speech • • • • Dysmorphic appearance Undescended testicles Constipation Seizures • Severity increases with copy number of MECP2 • Need to expand MECP2 testing criteria to include Xq28 MR All Wales Molecular Genetics Laboratory Thanks to Cardiff team: Ruth Lewis, Laz Lazarou, Sian Morgan, Hayley Archer, Angus Clarke, Referring clinicians: Sally Davies, Emma Baple, Ruth NewburyEcob, Frances Elmslie All Wales Molecular Genetics Laboratory
