α-thalassemia is an inherited globin gene disorder commonly found among the Chinese population. It is composed of both non-deletional and deletional α-globin gene mutations. Classical α-thalassemia presents with red cell microcytosis but silent cases with a normal mean corpuscular volume (MCV) are also seen. Routine laboratory testing methods for large-scale detection of silent α-thalassemia mutations are onerous and time-consuming. Furthermore, methods such as denaturing high performance liquid chromatography (HPLC) or denaturing gradient gel electrophoresis (DGGE) for scanning of point mutations are costly and they require post-PCR separation. High resolution melting (HRM) analysis is an economical, sensitive, and fast method for large scale point mutation scanning. Contamination is significantly reduced with HRM because the process is performed in a closed-tube environment and does not require post-PCR manipulation. We used HRM and multiplex gap-PCR analysis to determine the prevalence of silent α-thalassemia carriers in Hong Kong. Of the 223 hematologically normal blood samples scanned by Roche LightCycler 480®, HRM did not show any sample with a non-deletional α-globin gene mutation of clinical significance. α-multiplex gap-PCR analysis revealed 36 samples (16.1%) with single α-globin gene deletions. The detection of single α-globin gene deletions in samples with a MCV greater than 80 fL indicates that the previously reported prevalence of α-thalassemia mutations in our Chinese population based on MCV screening is under-estimated. The data also suggest that non-deletional α-thalassemia mutations presenting with a normal MCV are very rare, and they most likely present with microcytosis. The fact that most silent α-thalassemia mutations are due to large deletions supports the use of traditional molecular techniques such as gap-PCR for their detection. HRM can be used as an adjunct tool for large-scale population screening of non-deletional mutations. This study provides more accurate data on the prevalence of silent α-thalassemia carriers in the Hong Kong Chinese population. The information will facilitate genetic counseling and risk assessment in families carrying α-thalassemia mutations. / published_or_final_version / Pathology / Master / Master of Medical Sciences

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Obstetrics and Gynaecology / Master / Master of Philosophy

Homozygous α0-thalassemia is a serious autosomal recessive disorder with poor fetal outcome and severe maternal complications. Conventionally, prenatal diagnosis is performed by an invasive test. A non-invasive approach using serial ultrasonography can effectively reduce the need for invasive tests in unaffected pregnancies. For two-dimensional ultrasound prediction, a total of 777 at-risk fetuses were studied from 12 to 20 weeks between 1995 and 2006. At 12–15 weeks’ gestation, the highest sensitivity (98.3%) was achieved by the combination of fetal cardiothoracic ratio (CTR) and/or middle cerebral artery peak systolic velocity (MCA-PSV) at a false-positive rate of 15.8%. At 16–20 weeks’ gestation, the sensitivity of CTR was 100.0%, but the false-positive rate was 5.2%. In contrast, the false-positive rate of MCA-PSV alone was 1.4% and that of the combination of CTR and MCA-PSV was 0%, although their sensitivities were less than 65%. In a cross-sectional retrospective study of 546 samples at-risk and control (268 fetal and 278 neonatal cord blood), the degree of anemia was only mild in 27.5% of the affected fetuses (see chapter 3 for definition of mild anemia). Because MCA-PSV is not very predictive of mild anemia, this may be one of the reasons why MCA-PSV is not very sensitive in predicting an affected pregnancy. A total of 832 at-risk pregnancies were studied using same noninvasive approach at Maternal and Neonatal Hospital of Guangzhou (MNH) and Tsan Yuk Hospital (TYH). The overall sensitivity and specificity of the noninvasive approach was 100% and 95.6% respectively. At MNH, the need for an invasive test was reduced by 78.6%, and all the affected pregnancies were diagnosed before 24 weeks’ gestation. After adequate training and monitoring the quality of the subsequent ultrasound examinations, the results achieved at MNH were comparable to TYH, with at-risk pregnancies including the affected ones being seen at a more advanced gestation at MNH. In a retrospective review of 361 women at risk of carrying an affected fetus, 311 (86.2%) opted for the non-invasive approach using CTR and/or placenta. The cost saving of this non-invasive approach was relatively small (HK$ 2,651) in comparison to the cost of the whole prenatal screening program. On the other hand, the non-invasive approach was more expensive than the direct invasive approach for low MCV couples, as well as couples discordant for α-thalassemia and β-thalassemia. ages. These results support the adoption of non-invasive approach in which routine invasive test or karyotyping is no longer performed. A total of 106 at-risk pregnancies and normal controls were prospectively studied using three-dimensional ultrasonography. Placental volume (PV) at 11-14 weeks, and PV/CRL quotient at 9-14 weeks’ gestation of affected pregnancies were significantly greater than unaffected pregnancies (P<0.05). Using a cut-off point of 1.2ml/mm for PV/CRL quotient to predict an affected pregnancy, the sensitivity, and specificity was 96.2%, and 100.0% respectively. / published_or_final_version / Obstetrics and Gynaecology / Master / Doctor of Medicine