Invasive & non-invasive approaches for prenatal diagnosis of haemoglobinopathies: Experiences from India.

The thalassaemias and sickle cell disease are the commonest monogenic disorders in India. There are an estimated 7500 - 12,000 babies with β-thalassaemia major born every year in the country. While the overall prevalence of carriers in different States varies from 1.5 to 4 per cent, recent work has shown considerable variations in frequencies even within States. Thus, micromapping would help to determine the true burden of the disease. Although screening in antenatal clinics is being done at many centres, only 15-20 per cent of pregnant women register in antenatal clinics in public hospitals in the first trimester of pregnancy. There are only a handful of centres in major cities in this vast country where prenatal diagnosis is done. There is considerable molecular heterogeneity with 64 mutations identified, of which 6 to 7 common mutations account for 80-90 per cent of mutant alleles. First trimester foetal diagnosis is done by chorionic villus sampling (CVS) and DNA analysis using reverse dot blot hybridization, amplification refractory mutation system (ARMS) and DNA sequencing. Second trimester diagnosis is done by cordocentesis and foetal blood analysis on HPLC at a few centres. Our experience on prenatal diagnosis of haemoglobinopathies in 2221 pregnancies has shown that >90 per cent of couples were referred for prenatal diagnosis of β-thalassaemia after having one or more affected children while about 35 per cent of couples were referred for prenatal diagnosis of sickle cell disorders prospectively. There is a clear need for more data from India on non-invasive approaches for prenatal diagnosis.

HPLC studies in hemoglobinopathies.

An accurate diagnosis of beta -thalassemia carriers, homozygous patients and identification of different structural hemoglobin variants is important for epidemiological studies as well as for management and prevention of the major hemoglobin disorders. There are many electrophoretic and chromatographic approaches for estimation of HbA2 and Hb F but cation exchange HPLC (CE-HPLC)using automated dedicated machines like the Variant Hb testing system have become the method of choice for these investigations. CE-HPLC also helps in the presumptive identification of many abnormal hemoglobin variants and has been useful for both neonatal screening of sickle cell disease as well as second trimester prenatal diagnosis of thalassemia by fetal blood analysis. Other applications of HPLC in hemoglobinopathies include separation of globin chains, measuring the ratio of gamma globin chains (Ggamma/Agamma) and the recently described denaturing HPLC for detecting mutations in both alpha and beta globin genes.

Detection of two rare β -thalassemia mutations [-90 (C → T) and CD 26 (C → T)] among Indians.

BACKGROUND : β -Thalassemia (β -thal) is present in practically every caste group in Indians. Molecular characterization of β -thal in these groups has revealed an extremely heterogeneous picture. AIM : To identify all the mutations and to detect the novel mutations using a versatile mutation detection technique. MATERIALS AND METHODS : Denaturing gradient gel electrophoresis (DGGE) has been established to scan the entire β -globin gene to localize the mutation followed by DNA sequencing for characterization. The DNA samples from two families referred to us either for prenatal diagnosis or for DNA studies were studied. RESULTS : Atypical DGGE patterns in fragments B & A indicating the presence of the mutation, have been detected in both the families. DNA sequencing revealed two rare patterns fragments with patterns in fragments β -thal mutations [CD 26 (C→T) and -90 (C→T)]. CONCLUSION : DGGE is a useful mutation detection technique to identify β -thal mutations among the heterogeneous Indian population.

Variable clinical severity of Hb E beta-thalassemia among Indians.

OBJECTIVE: The aim of this preliminary report was to look at the effect of genetic variations in the alpha, beta and gamma globin genes in 7 cases of hemoglobin E/beta-thalassemia with diverse clinical expression of the disease. METHODS: beta-thalassemia mutations were characterized by PCR and dot blot hybridization. G gamma gene polymorphism (Xmnl) was determined by PCR followed by restriction enzyme digestion and polyacrylamide gel electrophoresis. alpha genotyping was done by Southern blot hybridization. RESULTS: Six cases had a severe beta+ mutation [IVS 1 nt 5 (G-->C)] and one case had a beta zero mutation [F/S 41/42 (-CTTT)]. Hence, the beta-thalassemia mutation does not seem to contribute towards the clinical diversity. alpha-genotyping showed a single alpha-gene deletion of the rightward type in three of the five milder cases. The -158 G gamma (C-->T) substitution was present at least in heterozygous state (+/-) in all the milder cases. CONCLUSIONS: Deletional alpha thalassemia and presence of the -158 G gamma (C->T) substitution are the two factors which appear to be more important in decreasing the severity of the disease rather than the nature of the beta thalassemia mutation.

Prenatal diagnosis of haemophilia: a preliminary report.

BACKGROUND: Haemophilia A is the most common congenital bleeding disorder seen in man, affecting one in 5000 to 10,000 males. Because of the large size and heterogeneity of mutations in the factor VIII gene, direct detection of mutations is not practically feasible, except the recently detected intron 22 inversions. Hence, the indirect method of gene tracking using various polymorphic markers is the method of choice. Using this approach, we have performed antenatal diagnosis in four haemophilia A families. METHODS: The four families included 21 subjects who were used for gene-tracking analysis. Two families had a positive history with more than one member affected, while the remaining two families had a negative history with only one affected son. In all four families, the propositi and their affected relatives had severe haemophilia A with factor VIII:C less than 1%. All were negative for inhibitors. The polymorphic markers used were IVS 18 Bcl I, IVS 19 Hind III and the extragenic DXS 52 St 14 of the factor VIII gene. Prior to polymorphism analysis, the sex of the foetus was determined using Y chromosome-specific primers. All the analyses were carried out by polymerase chain reaction. RESULTS: Antenatal diagnosis in the four families showed three normal male foetuses and one normal female foetus. Two families provided evidence with only IVS 18 Bcl I and St 14 markers. One family provided information with only intron 19 Hind III marker. The fourth family provided information with all three markers. The coagulation parameters were almost in agreement with the results of DNA analysis. CONCLUSION: All three polymorphic markers yielded information. This suggests that these three markers can be effectively used in the antenatal diagnosis of haemophilia A in Indian families.

Prevalence of HBsAg carriers among some tribes of Madhya Pradesh.

Prevalence of HBsAg was determined in 1314 sera obtained from 11 different tribal populations of five districts of Madhya Pradesh. Reversed passive haemagglutination assay was used for screening showed a HBsAg carrier rate of 2.99 to 21.54 per cent among the various tribes. Significant regional variation was also observed.