A novel (A)γδß(0)-thalassemia caused by DNA deletion-inversion-insertion of the ß-globin gene cluster and five olfactory receptor genes: Genetic interactions, hematological phenotypes and molecular characterization.

OBJECTIVE: To report the phenotypes and genetic basis of a novel (A)γδß(0)-thalassemia found in Thai individuals with several forms of thalassemia. DESIGNS AND METHODS: An initial study was done in an adult Thai woman who had hypochromic microcytic red cells with unusually 100% Hb F. Extended study was carried out on her parents and another 17 unrelated individuals with elevated Hb F. Hb analysis was performed by capillary electrophoresis and DNA analysis was done using PCR. A novel diagnostic method based on multiplex PCR assays was developed. RESULTS: DNA analysis of the proband revealed the homozygosity for a novel deletion of 118.3 kb, removing the entire (A)γ, ψß, δ-, ß-globin and five olfactory receptor (OR) genes with an insertion of a 179 bp inverted DNA sequence located behind the OR52A5 gene located downstream and an insertion of 7 orphan nucleotides. Her parents were both carriers of this mutation. Further screening in suspected cases in our series unexpectedly led to identification of an additional 17 cases with this mutation in different genotypes including plain heterozygote, homozygote, compound heterozygote with Hb E, and double heterozygote with several forms of α-thalassemia. Hematological features associated with these genetic interactions are presented. CONCLUSIONS: Haplotype analysis indicated a single origin of this novel deletion-inversion-insertion (A)γδß(0)-thalassemia in the Thai population. Differentiation of this mutation and other high Hb F determinants documented previously could be done by using a developed multiplex PCR assay.

Rapid molecular characterization of Hb Queens and Hb Siam: two variants easily misidentified as sickle Hb.

OBJECTIVE: To establish a rapid differential diagnosis of hemoglobin (Hb) Queens and Hb Siam from other clinically relevant variants. DESIGN AND METHODS: Molecular and hematological features associated with two pregnant Thai women who were mistaken for Hb S were investigated. A simultaneous DNA diagnosis based on multiplex allele specific PCR approach was developed and tested with other common variants. RESULTS: Apart from mild anemia, the two subjects were generally healthy. DNA analysis identified that they were respectively carriers of Hb Siam [alpha15(A13)Gly-Arg] and Hb Queens [alpha34(B15)Leu-Arg]. A successful application of the multiplex allele specific PCR for differential diagnosis was demonstrated. CONCLUSION: Diagnosis of these clinically relevant hemoglobinopathies is problematic in the routine setting, and the method developed should prove useful in complementing routine Hb analysis for providing accurate diagnosis.