BACKGROUND: Noninvasive trisomy 21 detection performed by use of massively parallel sequencing is achievable with high diagnostic sensitivity and low false-positive rates. Detection of fetal... Show moreBACKGROUND: Noninvasive trisomy 21 detection performed by use of massively parallel sequencing is achievable with high diagnostic sensitivity and low false-positive rates. Detection of fetal trisomy 18 and 13 has been reported as well but seems to be less accurate with the use of this approach. The reduced accuracy can be explained by PCR-introduced guanine-cytosine (GC) bias influencing sequencing data. Previously, we demonstrated that sequence data generated by single molecule sequencing show virtually no GC bias and result in a more pronounced noninvasive detection of fetal trisomy 21. In this study, single molecule sequencing was used for noninvasive detection of trisomy 18 and 13.METHODS: Single molecule sequencing was performed on the Helicos platform with free DNA isolated from maternal plasma from 11 weeks of gestation onward (n = 17). Relative sequence tag density ratios were calculated against male control plasma samples and results were compared to those of previous karyotyping.RESULTS: All trisomy 18 fetuses were identified correctly with a diagnostic sensitivity and specificity of 100%. However, low diagnostic sensitivity and specificity were observed for fetal trisomy 13 detection.CONCLUSIONS: We successfully applied single molecule sequencing in combination with relative sequence tag density calculations for noninvasive trisomy 18 detection using free DNA from maternal plasma. However, noninvasive trisomy 13 detection was not accurate and seemed to be influenced by more than just GC content. Show less
Genomic DNA of three patients, born as healthy carriers and developing a late-onset severe transfusion-dependent beta-thalassemia major was studied by high density genome wide SNP array analysis. A... Show moreGenomic DNA of three patients, born as healthy carriers and developing a late-onset severe transfusion-dependent beta-thalassemia major was studied by high density genome wide SNP array analysis. A mosaic loss of heterozygosity for almost the entire 11p was found not attributable to deletions, but involving mosaicism for segmental paternal isodisomy of 11p. Mitotic recombination leading to mosaic segmental uniparental isodisomy on chromosome 11p in multiple tissues has been described as a molecular disease mechanism for a subset of sporadic Beckwith-Wiedemann syndrome cases. A similar mechanism also seems to be involved in causing late-onset disease in carriers of recessive mutations in other genes located in 11p, such as late-onset beta-thalassemia major and sickle cell disease. We suggest that the the loss of maternally imprinted IGF-2 and H19 genes may account for the selective advantage of hematopoietic cells containing this segmental paternal isodisomy of 11p carrying the beta-thalassemia mutation. Show less
Context: During meiosis I, the recombination frequency in the pseudoautosomal region on Xp and Yp (PAR1) in males is very high. As a result, mutated genes located within the PAR1 region can be... Show moreContext: During meiosis I, the recombination frequency in the pseudoautosomal region on Xp and Yp (PAR1) in males is very high. As a result, mutated genes located within the PAR1 region can be transferred from the Y-chromosome to the X-chromosome and vice versa. Patients: Here we describe three families with SHOX abnormalities resulting in Leri-Weill dyschondrosteosis or Langer mesomelic dysplasia. Results: In about half of the segregations investigated, a transfer of the SHOX abnormality to the alternate sex chromosome was demonstrated. Conclusions: Patients with an abnormality of the SHOX gene should receive genetic counseling as to the likelihood that they may transmit the mutation or deletion to a son as well as to a daughter. Show less
