Research Awards
Bruria Ben Zeev, M.D.
Eva Gak, Ph.D.
Sheba Medical Center, Israel
"Molecular diagnosis of Rett Syndrome: an alternative scheme"
1-Year Award: $50,000
Research Sponsor: Israel Rett Syndrome Center
Final Report (November 2005)
During the past five years, more than 100 patients have been admitted to the Israeli RTT cohort including patients with classical and atypical RTT, PSV, EEF and FF variants, patients with Angelman-like features and with other clinical indications reminiscent of RTT. Most of the cohort members have been diagnosed using standardized clinical criteria by the same pediatric neurologist at the Neuropediatric Clinic at the Sheba Medical Center, where they continue to attend for clinical follow-up. Our molecular backing of RTT includes analyses of MECP2 coding region, MLPA, XCI. Within this framework, we identified 55 patients with MECP2 sequence variations, including mutations at the known CpG hot-spots, 3'-end microdeletions and large rearrangements encompassing MECP2 gene region, as well as novel sequence variations. The latter include two maternally inherited variations that were present in conjunction with imbalanced XCI, wherein the variant X was preferentially activated in the patients and inactivated in the asymptomatic mothers, thus suggesting that these variations could be related to RTT phenotype. In addition, we detected a rare TG deletion of exon 1 slice-donor in two other classical patients. These efforts however did not provide diagnosis for the remainder of our cohort, including at least 10 patients with classical RTT and several atypical cases with strong indication of RTT.
In attempt to resolve the remainder of the cases, we developed a quantitative assay providing estimates of MECP2_e1 and _e2 expression levels in peripheral blood, which has been implemented in patients with known MECP2 mutations as well as patients with no mutation findings, the latter including few classical patients who have been referred to us by RSRF and Berge Minassian from the Hospital for Sick Children, Toronto. We observed that various mutations had distinct effects on MECP2 expression levels in the peripheral blood. Patients with the splice-donor mutation had significantly lower levels of both MECP2 isoforms, patients with deletions and nonsense mutations had slightly lower levels of MECP2_e1 or _e2, while patients with missense mutations and in-frame deletions had normal MECP2 expression levels. Preferential XCI additionally contributed to the inter-individual differences in MECP2 expression levels. Several classical and atypical patients with no previous mutation findings were found with lower MECP2 expression levels, which prompt to persist and search the regulatory regions of this gene for yet unknown mutations. For the meantime, these findings suggest that blood MECP2 expression levels reflect the patients' genetic and epigenetic status and may be used as an additional index of RTT diagnosis.
Bruria Ben Zeev, M.D.Eva Gak, Ph.D.
Sheba Medical Center, Israel
"Molecular diagnosis of Rett Syndrome: an alternative scheme"
1-Year Award: $50,000
Research Sponsor: Israel Rett Syndrome Center
Final Report (November 2005)
During the past five years, more than 100 patients have been admitted to the Israeli RTT cohort including patients with classical and atypical RTT, PSV, EEF and FF variants, patients with Angelman-like features and with other clinical indications reminiscent of RTT. Most of the cohort members have been diagnosed using standardized clinical criteria by the same pediatric neurologist at the Neuropediatric Clinic at the Sheba Medical Center, where they continue to attend for clinical follow-up. Our molecular backing of RTT includes analyses of MECP2 coding region, MLPA, XCI. Within this framework, we identified 55 patients with MECP2 sequence variations, including mutations at the known CpG hot-spots, 3'-end microdeletions and large rearrangements encompassing MECP2 gene region, as well as novel sequence variations. The latter include two maternally inherited variations that were present in conjunction with imbalanced XCI, wherein the variant X was preferentially activated in the patients and inactivated in the asymptomatic mothers, thus suggesting that these variations could be related to RTT phenotype. In addition, we detected a rare TG deletion of exon 1 slice-donor in two other classical patients. These efforts however did not provide diagnosis for the remainder of our cohort, including at least 10 patients with classical RTT and several atypical cases with strong indication of RTT.
In attempt to resolve the remainder of the cases, we developed a quantitative assay providing estimates of MECP2_e1 and _e2 expression levels in peripheral blood, which has been implemented in patients with known MECP2 mutations as well as patients with no mutation findings, the latter including few classical patients who have been referred to us by RSRF and Berge Minassian from the Hospital for Sick Children, Toronto. We observed that various mutations had distinct effects on MECP2 expression levels in the peripheral blood. Patients with the splice-donor mutation had significantly lower levels of both MECP2 isoforms, patients with deletions and nonsense mutations had slightly lower levels of MECP2_e1 or _e2, while patients with missense mutations and in-frame deletions had normal MECP2 expression levels. Preferential XCI additionally contributed to the inter-individual differences in MECP2 expression levels. Several classical and atypical patients with no previous mutation findings were found with lower MECP2 expression levels, which prompt to persist and search the regulatory regions of this gene for yet unknown mutations. For the meantime, these findings suggest that blood MECP2 expression levels reflect the patients' genetic and epigenetic status and may be used as an additional index of RTT diagnosis.