An Evaluation for the Causes of Reduced Hb A2 and the Molecular Characterization of HBD Variants in Hong Kong.

Prenatal screening of ß-thalassemia (ß-thal) carriers is based on the hallmark phenotype of microcytosis and raised Hb A2. The unanticipated birth of ß-thal major (ß-TM) offspring to ß-thal carriers who were misdiagnosed during prenatal screening have been reported. A subset of these resulted from the masked phenotype due to the coinheritance of HBD variants. In a broader sense, the causes of reduced Hb A2 in thalassemia screening, the prevalence and spectrum of HBD variants in Hong Kong remain to be characterized. Over a 13-month period, a total of 2982 samples were referred for thalassemia screening. Surplus samples with reduced Hb A2 levels (2.0%) were evaluated. HBD variations were assessed by direct sequencing. Sixty-six samples were tested. Hb H disease, HBD variants, α-thalassemia (α-thal) trait and iron deficiency were detected in 40 (60.6%), 12 (18.2%), eight (12.1%) and seven (10.6%) samples, respectively. Seven samples carried more than one of the mentioned conditions. The cause remained elusive in seven samples. Thirteen HBD variants were detected and two were recurrent, including HBD: c.-127T>C [-77 (T>C)] and HBD: c.314G>A (Hb Chori-Burnaby). A novel nonsense variant HBD: c.262C>T [codon 87 (C>T)] was detected in cis with HBD: c.-127T>C. Overall, the prevalence of HBD variants was 0.4%. This study advanced our understanding of the causes of reduced Hb A2 in clinical practice and identified hereditary disorders of α- and δ-globin genes as the prevailing causes. It established the landscape of HBD variations in our locality and highlighted the pitfall of phenotypic screening of ß-thal carriers.

Distinct mutation spectrum, clinical outcome and therapeutic responses of typical complex/monosomy karyotype acute myeloid leukemia carrying TP53 mutations.

The present study aimed to define a subtype of complex/monosomal karyotype (CK/MK) acute myeloid leukemia (AML) by its distinct clinical features, p53 signaling and responses to p53 targeting agents. Ninety-eight young adults (range: 21-60 years; median: 49 years) with CK/MK AML were studied. They received standard induction, consolidation and allogeneic hematopoietic stem cell transplantation from siblings or matched unrelated donors if available. Chromosomal abnormalities most commonly affected chromosome 5 (30%), 7 (22%) and 17 (21%). Next generation sequencing of a 54-myeloid gene panel were available in 76 patients. Tumor protein 53 (TP53) mutations were most common (49%) and associated with the presence of -5/5q- (P < .001) and -17/17p- (P < .001), but not -7/7q- (P = .370). This "typical" CK/MK AML subtype was associated with significantly lower presenting white cell counts, higher number of karyotypic abnormalities, and inferior leukemia-free and overall survivals, compared with CK/MK AML without the typical features. Blood or bone marrow samples from typical CK/MK AML patients showed defective p53 signaling upon induction by etoposide. In vitro drug sensitivity analysis showed that they were sensitive to APR-246 that targeted mutant p53, but resistant to MDM2 antagonist MI-77301. Novel therapeutic strategies targeting TP53 mutations in CK/MK AML should be developed and tested in clinical trials.

First Report of Hb Kent [ß37(C3)Trp→Cys (TGG>TGC) HBB: c.114G>C] in a Chinese Family.

We report a novel HBB: c.114G>C mutation in a Chinese family. This mutation resulted in a ß37(C3)Trp→Cys amino acid substitution and was synonymous with Hb Kent, a hemoglobin (Hb) variant that was reported exclusively in patients of European descent. Though Hb Kent has a normal oxygen affinity and molecular stability, it has a characteristic dual variant appearance on cellulose acetate electrophoresis (CAE) and high performance liquid chromatography (HPLC) caused by the posttranslational modification of cysteine. We also report the phenotypic expression of this variant when coinherited with the Southeast Asian (- -SEA) double α-globin gene deletion.

A Multi-locus Approach to Characterization of Major Quantitative Trait Loci Influencing Hb F Regulation in Chinese ß-thalassemia Carriers.

Genetic association studies showed that Hb F is under the influence of major quantitative trait loci (QTL) in ß-thalassemia (ß-thal) carriers. Single nucleotide polymorphisms (SNPs) at three major QTLs, BCL11A, HBS1L-MYB intergenic region and XmnI-HBG2 were individually validated in univariate models. However, their relative effect sizes on Hb F regulation are unknown. We genotyped 99 Chinese ß-thal carriers for the three major QTLs and performed genetic association studies using three different statistical models, including mass univariate analysis, multivariate linear regression and partial least square regression structural equation modeling (PLS-SEM). Performances of the three models were compared and effect sizes of the three QTLs in a multivariate model were assessed. Traditional mass univariate analysis and multivariate linear regression showed limited statistical power in our small cohort and the latter was constrained by multicollinearity. Partial least structural equation modeling showed significant positive associations of each QTL (p <0.05) with Hb F regulation, together explained 34.4% of variance. The HBS1L-MYB intergenic region polymorphism (HMIP) demonstrated the highest effect on Hb F prediction with effect size f2 0.294. PLS-SEM offered a statistically powerful multivariate model for multi-locus genetic association studies. We reproduced findings of previous studies with a much smaller cohort and demonstrated HMIP as the strongest regulator of Hb F in Chinese ß-thal carriers.