The Importance of Prenatal Diagnosis By Chorionic Villous Sampling in Detecting and Preventing Beta Haemoglobinopathies in a Resource Poor Setting: A Report from Eastern Part of India

Introduction: β Haemoglobinopathy, is one of the commonest inherited disorders, with a higher prevalence in the eastern part of India. In view of the lack of facilities for allogeneic stem cell transplantation, including financial constraints, this disease is considered to be incurable in this part of India. So, preventing the birth of a symptomatic Thalassemic child is the best way to prevent the disease, considering the immense medical, social & financial implications in the community. Therefore, prenatal diagnosis is the most important tool for detecting & preventing symptomatic haemoglobinopathies.

Objectives: To detect the status of haemoglobinopathies in the foetus of carrier or affected parents, so as to prevent the birth of symptomatic patients with Thalassemia & other haemoglobinopathies.

Material & Methods: This is a retrospective analysis of an ongoing registry data of routine prenatal diagnosis of haemoglobinopathy, conducted at NRS Medical College, Kolkata, over a period of approximately 4 ½ years (September,2013-April,2018). The process involves, collection of Ultrasound guided chorionic villous samples (CVS) by an Obstetrician between 12-16 weeks of gestation (maximum up to 19 weeks). Considering the prevalence of specific mutations in this part of India, a total of 25 β mutations are analysed by ARMS-PCR, using specific probes. Some of the common mutations tested are: IVS1-5(G→C), 619bp del, IVS 1-1(G→T), CD 30(G→C), CD 26(G→A) & CD6 (A→T).

Results: Total number of CVS were 407(407 mothers were tested), of which 329 samples (80.8%) showed presence of β haemoglobinopathy mutations, & 78(19.2%) did not have any mutations. Among the mutated genotype, heterozygous carrier state was detected in 232(57%), & homozygous/ compound heterozygous state(affected) was detected in 92 foetuses (22.6%). Among the carriers, β Thalassaemia trait was most common(n=185,45.45%), followed by HbE Trait(n=41,10.07%). HbS trait(n=3), HbD trait(n=1) & δβ Thalassemia trait (n=2) were rarely detected. Among the affected foetuses, 44 had compound heterozygous genotype (10.8%), majority being HbEβ thalassemia (n=42,10.3%), followed by δβ-β Thalassemia(n=1) & HbSβ Thalassemia(n=1). The remaining 48 affected cases were homozygous β Thalassemia Major (11.7%). Of the 92 affected pregnancies, 91(22.35%) had been counselled for medical termination of pregnancy (MTP). One case of δβ-β Thalassemia, a milder phenotype, was excluded from MTP counselling. Total number of β mutations detected (both homozygous & heterozygous states) were n=373, and the commonest was IVS1-5(G→C) (n=244,65.4%), followed by CD 26(G→A) (n=85,22.78%), CD 30(G→C) (n=9,2.4%), CD 41/42(-CTTT) (n=8,2.1%), CD 15(G→A) (n=8,2.1%) & CD8/9 (+G) (n=4,1.1%). Rarer β mutations detected were CD15(-T) (n=4,1.1%), CD16(-C) (n=1), CD6 (A→T) (n=4,1.1%), βD-PunjabCD121 (G→C) (n=3) & Asian Indian inversion deletion Gγ (Aγδβ)0(n=2).

We know that sometimes maternal cell contamination may occur during villous sampling. So, at the time of childbirth, cord blood was collected & β mutation studies were re-performed. If this could not be done, an HPLC was conducted when the child was >1year old. We have data of 26 children & each time the results have corroborated with the primary CVS sampling data.

Among both male and female parents(n=814), the commonest genotype was β Thalassemia Trait (n=621, 76.3%). Among the female parents(n=407), some of the other genotypes were HbE Trait (n=94,23.09%) & HbS trait(n=4,0.98%). Among the male parents(n=407), HbE Trait(n=70,17.19%) was the 2^nd most common abnormality, few of the other genotypes being: HbS Trait (5,1.2%), β Thalassemia major (n=3,0.73%) & HbE homozygous disease (n=3, 0.73%).

Conclusions: From this cohort, total affected (homozygous/compound heterozygous) foetuses are 92(22.6%). β Thalassemia Major (11.7%) is the most common affliction, followed by HbEβ thalassemia (10.3%) & δβ - β Thalassemia. An attempt at prevention of birth of at least 91(22.35%) future thalassemia patients has been done by means of MTP.

Ours is an ongoing registry data and we are following up the children by conducting cord blood mutation studies or HPLC (>1year old child), to study the precision and accuracy of our CVS sampling results. So far there has been 100% concordance. One of the limitations of our study is lesser number of reconfirmation of the born children, in view of social and financial constraints.