Combined Gap-Polymerase Chain Reaction and Targeted Next-Generation Sequencing Improve α- and β-Thalassemia Carrier Screening in Pregnant Women in Vietnam

Vietnam has a high thalassemia burden. We collected blood samples from 5880 pregnant Vietnamese women during prenatal health checks to assess thalassemia carrier frequency using combined gap-polymerase chain reaction (gap-PCR) and targeted next-generation sequencing (NGS). Thalassemia carriers were identified with prevalence of 13.13% (772), including 7.82% (460) carriers of α-thalassemia (α-thal), 5.31% (312) carriers of β-thalassemia (β-thal), and 0.63% (37) concurrent α-/β-thal carriers. Deletional mutations (368) accounted for 80.0% of α-thal carriers, of which, --^SEA (Southeast Asian) (n = 254; 55.0%) was most prevalent, followed by the -α^3.7 (rightward) (n = 66; 14.0%) and -α^4.2 (leftward) (n = 45; 9.8%) deletions. Hb Westmead (HBA2: c.369C>G) (n = 53) and Hb Constant Spring (Hb CS or HBA2: c.427T>C) (in 28) are the two most common nondeletional α-globin variants, accounting for 11.5 and 6.0% of α-thal carriers. We detected 11 different β-thal genotypes. Hb E (HBB: c.79G>A) (in 211) accounted for 67.6% of β-thal carriers. The most common β-thal genotypes were associated with mutations at codon 17 (A>T) (HBB: c.52A>T), codons 41/42 (-TTCT) (HBB: c.126_129delCTTT), and codon 71/72 (+A) (HBB: c.217_218insA) (prevalence 0.70%, 0.68%, and 0.2%, respectively). Based on mutation frequencies calculated in this study, estimates of 5021 babies in Vietnam are affected with clinically severe thalassemia annually. Our data suggest a higher thalassemia carrier frequency in Vietnam than previously reported. We established that combining NGS with gap-PCR creates an effective large-scale thalassemia screening method that can detect a broad range of mutations.

Hb Bart's Hydrops Fetalis Syndrome and Hb H Disease Caused by Deletional Chiang Rai (- -CR) α0-Thalassemia in Two Unrelated Thai Families

α⁰-Thalassemia (α⁰-thal) Chiang Rai (- -^CR; NC_000016.10: g.144215_188843del) was identified as a novel 44.6 kb deletional type of α-thalassemia (α-thal), removing all α-like globin genes. However, little is known about the deleterious effects of this genetic disorder, particularly when it is combined with other types of thalassemia. We performed molecular analysis of the - -^CR deletion using gap-polymerase chain reaction (gap-PCR) in two independent families residing in Phayao and Chiang Mai, Thailand, with an unknown causative mutation for Hb Bart's hydrops fetalis syndrome and Hb H disease. Five out of seven individuals were diagnosed to be heterozygous for the - -^CR deletion. Of these, two also carried Hb H disease with compound heterozygosities for - -^CR and -α^3.7 (rightward) deletions. However, hematological parameters of the - -^CR carriers displayed microcytic hypochromic anemia that is comparable to other α⁰-thal traits. Although the prevalence of - -^CR has never been elucidated in a specific population, our study demonstrated that genotyping for - -^CR might be considered as an additional investigation for unexplained Hb Bart's hydrops fetal syndrome and Hb H disease.

Umbilical Cord Blood Screening for the Detection of Common Deletional Mutations of α-Thalassemia in Bangladesh

α-Thalassemia (α-thal) is assumed to be very prevalent in Bangladesh. We aimed to assess the prevalence of the disease in the country and provide a model for α-thal newborn screening in Bangladesh. We collected umbilical cord blood (UCB) samples from 413 unrelated newborns in Bangladesh. Demographic information, blood indices, osmotic fragility, serum iron (Fe), and zinc (Zn) levels were evaluated for all the subjects. All subjects underwent a polymerase chain reaction (PCR)-based diagnosis for α-thal status, followed by a multiplex gap-PCR-based identification of the deletion type present. Sixty-seven subjects had at least one α-thal deletion (16.22%). We observed that -α^3.7 (rightward), - -^SEA (Southeast Asian), -α^4.2 (leftward), - -^MED (Mediterranean) and - -^THAI (Thailand) deletions were the most common α-globin deletions present in the country, with the -α^3.7 (n = 37) and - -^SEA (n = 18) being most prevalent. The osmotic fragility test (OFT) could predict the presence of α-thal deletions with over 98.0% sensitivity. Complete UCB count analysis revealed significant differences between healthy subjects and subjects with α-thal deletions. Although the iron level was almost the same (108.0 vs. 105.7 µg/dL), a reduced level of Zn (98.6 vs. 71.8 µg/dL, p < 0.01) was observed in the cord blood-derived serum of the subjects with α-thal deletions. Moreover, parental age at the time of delivery, gestational period, and birth weight was lower in the subjects with α-thal deletions. This study provides partial information on the epidemiology of α-thal in Bangladesh and describes a model for α-thal newborn screening in the country.

β-Thalassemia Intermedia Caused by Compound Heterozygosity for Hb Lepore-Hollandia and β-Thalassemia is Rare in the Indian Population

Compound heterozygosity for one of the Hb Lepore mutations and β-thalassemia (β-thal) is a rare cause of non transfusion-dependent thalassemia. We report a 4-year-old boy who presented clinically as homozygous/compound heterozygous β-thal intermedia (β-TI), an impression that was corroborated by the initial hemoglobin (Hb) high performance liquid chromatography (HPLC). However, the correct diagnosis of a rare compound heterozygous Hb Lepore-Hollandia/β-thal was revealed after parental studies and molecular analyses including β-globin gene sequencing. Our patient highlights the importance of a logical stepwise multi modality approach and the vital importance of parental screening and molecular studies in accurate characterization of complex hemoglobinopathies. Correct diagnosis is especially crucial if pre natal detection is anticipated for future pregnancies. Molecular analyses alone may not compensate for the unavailability of parental testing. This is because the molecular results may be misinterpreted, especially if limited tests are conducted. The infrequent prior reports of this combination from distant parts of the Indian subcontinent suggests that the origin of Hb Lepore-Hollandia from sporadic mutations occurs in isolated families.