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

Revisiting and updating molecular epidemiology of α-thalassemia mutations in Thailand using MLPA and new multiplex gap-PCR for nine α-thalassemia deletion

“…Moreover, we report for the first time, genotypes such as Hb H disease (-- CR /-α 4.2 ) and Hb H CS disease (-- CR /α CS α). The clinical phenotype of deletional Hb H disease (-- CR /-α 3.7 and -- CR /-α 4.2 ) was similar to previously reported 20 deletional Hb H genotypes and involved moderate anemia without requiring transfusion (Table 2 ). Non-deletional Hb H disease patients had compound heterozygous α 0 -thalassemia (-- CR ) with Hb CS, and presented with moderate to severe anemia and required regular blood transfusions (1–2 units) every 4–5 months.…”

“…In Thailand, the -- CR deletion has been reported in several studies involving northern populations. Notably, co-inheritance of the -- CR deletion with other α 0 -thalassemia or α + -thalassemia alleles results in Hb Bart’s hydrops fetalis (-- SEA /-- CR ) and Hb H disease (-- CR /-α 3.7 ), respectively 12 , 20 . Our study is the first report of southern Thailand patients with the same genotype, both Hb Bart’s hydrops fetalis (-- SEA /-- CR ), and Hb H disease (-- CR /-α 3.7 ).…”

“…A rare α 0 -thalassemia mutation (-- CR and -- SA ) was identified in the Thai population a few years ago 11 , 12 , 20 . However, information concerning the frequency of this mutation among the Thai population spanning all parts of the country remains limited.…”

Development of molecular diagnostic platform for α0‐thalassemia 44.6 kb (Chiang Rai, ‐‐CR) deletion in individuals with microcytic red blood cells across Thailand

“…In Thailand, this variant was called α 0 ‐thalassemia Chiang Rai deletion (‐‐ CR ). To the best of our knowledge, ‐‐ 44.6 or ‐‐ CR was currently noticed only in southern China and frequently identified in northern Thailand with a remarkable allelic spectrum (Ruengdit et al., 2020, 2022, 2021). This may be due to the migration and common ancestors in which northern Thai is genetically close to southern Chinese (Kutanan et al., 2021; Vichinsky, 2005).…”

“…Recently, α 0 -thalassemia 44.6 kb deletion (-- 44.6 ; NC_000016.10:g.144,215_188,841) was first described in southern China (Wang et al, 2017) and has been identified in northern Thailand as Chiang Rai deletion (--CR ) with 1.71% frequency (Ruengdit et al, 2020;Ruengdit et al, 2022). Similar to other α 0 -thalassemia carriers, the --CR carriers displayed asymptomatic with apparent microcytic red blood cells; however, compound heterozygosity of this variant and --SEA or -α 3.7 likewise can cause Hb Bart's hydrops fetalis and HbH disease, respectively (Ruengdit et al, 2020(Ruengdit et al, , 2021. The --CR frequency fell between 1% and 5% in this population.…”