Challenges in Thalassemia Carrier Detection in a Low Resource Setting Area of Eastern Indonesia: the Use of Erythrocyte Indices

Molecular and Haematological Characteristics of alpha-Thalassemia Deletions in Yogyakarta Special Region, Indonesia

Background

alpha-Thalassemia is caused primarily by deletions of one to two alpha-globin genes and is characterized by absent or deficient production of alpha-globin protein. The South-East Asia (SEA) deletion, 3.7-kb and 4.2-kb deletions are the most common causes. The present study aimed to observe the molecular characteristics of this common alpha-Thalassemia deletions and analyse its haematological parameter.

Methods

Blood samples from 173 healthy volunteers from thalassemia carrier screening in Yogyakarta Special Region were used. Haematological parameters were analysed and used to predict the carrier subjects. Genotype of suspected carriers was determined using multiplex gap-polymerase chain reaction and its haematological parameters were compared. The boundary site of each deletion was determined by analysing the DNA sequences.

Results

Seventeen (9.8%) of the volunteers were confirmed to have alpha-Thalassemia trait. Of these, four genotypes were identified namely -α^3.7/αα (58.8%), -α^4.2/αα (5.9%), -α^3.7/-α^4.2 (5.9%) and - -^SEA/αα (29.4%). The 5' and 3' breakpoints of SEA deletion were located at nt165396 and nt184700 of chromosome 16, respectively. The breakpoint regions of 3.7-kb deletion were 176-bp long, whereas for 4.2-kb deletion were 321-bp long. The haematological comparison between normal and those with alpha-Thalassemia trait genotype indicated a significant difference in mean corpuscular volume (MCV) (p< 0.001) and mean corpuscular haemoglobin (MCH) (p< 0.001). As for identifying the number of defective genes, MCH parameter was more reliable (p= 0.003).

Conclusion

The resultant molecular and haematological features provide insight and direction for future thalassemia screening program in the region.

Cell-free fetal DNA as a non-invasive method using pyrosequencing in detecting beta-globin gene mutation: A pilot study from area with limited facilities in Indonesia

BACKGROUND

Thalassemia is a monogenic, autosomal recessive, inherited disorder of the red blood cells caused by mutations or deletions in the globin gene. Approximately 6-10% of the Indonesian population carries the β-globin gene mutation; however, premarital screening is rarely conducted, and antenatal screening is optional. We explored the use of cell-free fetal DNA (cffDNA) as a potential non-invasive method of detecting the fetal β-globin gene mutation prenatally in pregnant women.

MATERIALS AND METHODS

Pregnant mothers (n = 10), who were known carriers of thalassemia and who had a history of having borne a baby with thalassemia major, and their carrier husbands (n = 4) were recruited after providing consent. EDTA blood was drawn, and maternal DNA, including cffDNA, and paternal DNA were isolated. Maternal contamination tests were conducted using the variable number tandem repeat test for ApoB and D1S80 loci. Allele quantification was performed by pyrosequencing. Known mutations from the bio-archived DNA of patients with thalassemia major (n = 16) were run alongside as a control.

RESULTS

In total, 7 out of 10 cffDNA successfully passed the maternal contamination test. The results of the allele quantification showed that six fetuses were predictive carriers of IVS1nt5 and one was predictive normal, in line with the allele quantification for the bio-archived DNA from patients with thalassemia major. The minimum threshold percentage for mutant A allele at cd26 was 32%, mutant T allele at IVS1nt1 was 23%, and mutant C allele at IVS1nt5 was 39%.

CONCLUSION

Taking cffDNA from the mother's blood proved useful as a non-invasive means of detecting the β-globin gene mutation using pyrosequencing allele quantification. This non-invasive method is of great interest for prenatal diagnosis in settings with limited facilities, as it minimizes the risk of abortion. Further study of other mutations of the β-globin gene is needed.