Background:
Rett syndrome (RTT) is a severe progressive neurodevelopmental disorder that presents early in childhood and affects primarily females (OMIM #312750). This X-linked dominant disorder affects 1:10,000-1:15,000 girls. In classic RTT, normal growth and development occurs during approximately the first 6-18 months of life. This is followed by an arrest in development and subsequent progressive loss of acquired motor skills and language and the onset of stereotypical hand movements. Other variants of RTT include congenital Rett syndrome, “forme fruste” and preserved speech variant. RTT has generally been considered to be lethal in males, but recent studies have identified males with RTT with varying degrees of severity. Rett syndrome is caused by mutations in the methyl CpG binding protein 2 (MECP2) located at chromosome Xq28. This comprehensive analysis includes Sequencing and Deletion/ Duplication Analysis.
Reasons for Referral:
- Confirmation of clinical diagnosis in patients with classical Rett syndrome.
- Diagnostic testing in patients with variants of Rett syndrome.
- Testing of family members of Rett syndrome patients or those who have non-syndromic mental retardation or autistic spectrum disorder.
- Prenatal diagnosis.
Methodology:
Sequencing can be performed by either method below:
Sanger Sequencing: Sequencing of MECP2 is carried out by amplification of all exons and intron/exon boundaries followed by bi-directional Sanger sequencing. The sensitivity of full gene sequencing is estimated to be approximately 99% for single nucleotide substitutions and small insertions/deletions. All nucleotide changes are analyzed within the context of current databases and literature to predict pathogenicity.
NGS Sequencing: Next generation sequencing will analyze the exons or coding regions of MECP2 using Illumina NextSeq 500 technology. Samples are prepared using hybridization probes to enrich exonic regions. Promoter, intronic, etc. regions are not assessed on our assay, but may contain variants that impact gene function.
80% detection rate in females with classical Rett syndrome.
Deletion/Duplication: Gross deletion and duplication analysis is done by MLPA (multiplex ligation-dependent probe amplification).
Specimen Requirements:
Blood: EDTA or ACD (Solution Aor B):
- Adult: 5mL
- Child: 5mL
- Infant: 2-3mL
Saliva: 2 ORAgene Saliva Kit(s) (OGR-500)
Skin Fibroblast: Punch Biopsy, or 2 T-25 confluent flasks
Prenatal:
- Direct Amniotic Fluid (10-20mL)
- Direct CVS
- Cultured Amnio or CVS (2-T25 flasks)
DNA: 1-2µg at a minimum of 50-100ng/µL (DNA must be extracted in a CLIA-certified laboratory or a laboratory meeting equivalent requirements as determined by the CAP and/or CMS)
Notice Regarding Molecular Genetic Testing on CVS or Amniotic Fluid Specimens:
- Maternal cell rule-out testing will be performed on all prenatal specimens received.Please provide maternal blood in addition to the fetal specimen.Additional charges apply for the maternal cell rule-out test.
- All genetic testing performed on Direct CVS or Direct Amniotic Fluid specimens will be confirmed on cell cultures prepared by Knight Diagnostic Laboratories.Cell cultures will be prepared from the specimen received.Additional charges apply for confirmatory testing.
For routine testing of blood, saliva and buccal swabs, KDL does NOT accept samples from patients within two (2) weeks of a packed cell/platelet transfusion or within four (4) weeks of a whole blood transfusion. For extraordinary circumstances, where testing must be performed outside of the above windows, please contact our lab.
A REQUISITION FORM MUST ACCOMPANY ALL SAMPLES. Please include detailed clinical information, including ethnicity, clinical history, and family history.
Test Performed (Days):
Weekly
Turn Around Time:
14 – 21 days
Shipment Sensitivity Requirements:
- Package and ship specimen to remain cool, but not frozen.
- Please use the cold pack provided in the kit.
- Ship via overnight express, using the FedEx priority overnight label provided.
- Contact Client Services for shipping kits and instructions at (855) 535-1522.
References:
Additional Info:
Prior to any genetic testing we recommend genetic counseling. Please contact Client Services at (855) 535-1522 for forms and information about prenatal diagnostic testing.