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November 2007, Volume 57, Issue 11

Original Article

Prenatal diagnosis of ß-Thalassaemia by Chorionic Villous Sampling

Samina Tasleem  ( Rawalpindi General Hospital, Rawalpindi. )
Huma Tasleem  ( Shifa College of Medicine, Islamabad )
Mehfooz Ahmed Siddiqui  ( Rawalpindi General Hospital, Rawalpindi )
Malik Muhammad Adil  ( Shifa College of Medicine, Islamabad )
Yasmin Rashid  ( Ganga Ram Hospital Lahore )

Abstract

Objective: To establish intrauterine diagnosis of thalassaemia major in couples with thalassaemia trait by chorionic villous sampling.
Methods: A total of 60 couples with children suffering from transfusion dependent ß-thalassaemia or couples who were known carriers of ß-thalassaemia were included in this study. The standard procedure was followed for the collection of samples which was finally transferred in appropriate medium to Armed Forces Institute of Pathology Rawalpindi for detection of thalassaemia mutation.
Results: After DNA analysis of the submitted samples, no thalassaemia mutation was detected in the foetus in 24 cases. In 8 cases foetus were heterozygote for thalassaemia having a single mutation. In 28 cases, foetus were homozygous for beta-thalassaemia.
Conclusion: Appropriate and extensive screening, accurate detection and counseling of at risk couples, along with antenatal diagnosis is a promising strategy for the reduction of mortality and morbidity from thalassaemia in countries where it is prevalent. Based on these results, it can be concluded that prenatal diagnosis of ß-thalassaemia for prevention can be done using chorionic villous sampling (JPMA 57:528:2007).

Introduction

Thalassaemia was first identified as a clinical entity in 1925 by Thomas Cooley and Pearl Lee.1 They examined four children from Greece and Italy who were having anaemia along with characteristic facies, splenomegaly, bone deformities with profound erythroblastosis in blood and familial incidence.2 More than a decade later Wintrobe and colleagues described milder forms of Cooley's anaemia. They noticed that milder manifestations of this disorder were present in both parents of children with classic Cooley's anaemia.3
Thalassaemias are a heterogeneous group of disorders in which the production of normal haemoglobin is partly or completely suppressed because of diminished synthesis of one or more globin chains.4 According to the chain, which is deficient, several types of thalassaemia have been described. The common types of clinical importance are a, ß and g thalassaemias.5
ß-Thalassaemia is one of the most common single gene disorders worldwide.6,7 Most of the children affected with this lethal disorder are born in developing countries.7

The report of DNA diagnosis was received after four days. In case the foetus was homozygous for ß-thalassaemia mutation, facility for termination of pregnancy soon after the diagnosis was provided.
A record was maintained in all cases to document the possible complications in later months of gestation and also the outcome at birth.

Results

The mean age of the study population was 30.5 ± 5.82 years ranging from 22 to 45 years.
The women included in this study, were married for a period of 10 months to 24 years with the mean of 9.0 ± 5.7 years and median was 8 years. Most of the women included in the study had conceived more than once in the past.
The couples included in the study came from different ethnic groups, 24 were Punjabi, 20 Pathans and 16 were Kashmiris. Partners were first cousins in 32 cases, distant relatives in 16 cases and were unrelated in 12 cases.
Eight couples had two previous affected children, 48 had one previous affected child and 4 couples had conceived for the first time. In the single couple who had not had an affected child in the past, partners were first cousins, had one affected cousin with transfusion dependent thalassaemia major and on screening were found to be carriers for beta-thalassaemia mutation before marriage, therefore opting for prenatal diagnosis and chorionic villous sampling after they conceived.
All women had singleton pregnancy with gestational age ranging from 10-12 weeks. No congenital abnormality was detected. Four women had a spontaneous foetal loss on 3rd day after the chorionic villous sampling. Twelve complained of mild pain in abdomen - especially at the site of abdominal insertion of the CVS needle. Pain was transient and self limiting which did not require medication and settled once the patient was reassured.
Four women had slight PV bleeding following the procedure on first and second day.
After DNA analysis of the submitted samples, no thalassaemia mutation was detected in the foetus in 24 cases. In 8 cases, foetus were heterozygote for thalassaemia having a single mutation. In 28 cases, foetus were homozygous for beta-thalassaemia, which were subjected to termination.

Discussion

ß-thalassaemia is one of the commonest inherited disorders in Pakistan.17 One out of every twenty individuals carries a gene for ß-thalassaemia. Since population is rapidly increasing in Pakistan, therefore birth of large number of new cases is expected every year. High prevalence among Punjabis are inconsistent with the study done in Department of Genetics, Sanjay Gandhi Post Gratuate Institute of Medical Sciences,India, where high prevalence was found among Sindhi, Punjabis, Gujratis and Bengalis.18 It is estimated that in our country with a population of 150 millions, five thousand children have the likelihood to be born with homozygous ß -thalassaemia. A large number of these affected children die before diagnosis in the absence of a national program for diagnosis, treatment and prevention of ß -thalassaemia. Among those who are diagnosed, vast majority of children are not treated adequately and have a very poor quality of life and limited survival.7 Haemoglobin (beta) thalassaemia is an important cause of childhood disease in south Asia.19
Standard treatment of ß -thalassaemia includes blood transfusion according to internationally accepted standards to maintain a mean haemoglobin level of 12 gm/dl, and iron chelating therapy with desferrioxamine to control the deleterious effects of progressive iron overload. Such treatment has significantly improved not only the survival but also the quality of life for thalassaemic children. Now more than 90% survival beyond 30 years of age is reported from the European centers.20 To achieve this target, huge amount of material resources, state of the art expertise of doctors and other health workers looking after thalassaemic children and reliable health delivery system are primary requirements.
Like all other developing countries, the Pakistani, population is growing rapidly, health delivery system is in shambles, poverty is escalating (independent indicators showing absolute poverty rate of over 35%) and resources are limited. This will practically become impossible to provide standard treatment to all the affected children. Therefore the burden of the illness should be reduced and strategies implemented to control birth of new affected children.21 Dramatic decline in the incidence of ß-thalassaemia in countries with highest incidences in Europe i.e. Cyprus, Greece, Italy and Sardinia, can serve as a sound foundation to develop a reliable and effective strategy for prevention. WHO guidelines on control of haemoglobinopathies provide useful guidelines to develop a national programme to control ß-thalassaemia in our country.22
Such programmes involve identification of all individuals carrying a gene for ß -thalassaemia, counseling of these carriers and prenatal diagnosis by chorionic villous sampling in situations where both parents are carriers.23
Individuals at risk to be carriers can be identified by simple but specific blood tests. Once identified, they need to be counseled by experienced persons about the options and risks in future.24
Prenatal diagnosis was previously done by multiple methods but now the preferred method is detection of ß-thalassaemia mutation by amplification of foetal DNA - obtained by chorionic villous biopsy.21  Prenatal diagnosis of ß-thalassaemia by the Reverse Dot Blot (RDB) and Amplification refractory mutation system (ARMS) technique can prevent the birth of an affected child in developing countries in which ß-thalassaemia is quite prevalent.18  . Since initial reports of prenatal diagnosis in 1994, now this facility is provided to at risk couples at number of centers in the country.17
Results of this study show that chorionic villous sampling done at 10-12 weeks of gestation by transabdominal approach is a simple and safe technique. Though, like all other medical and surgical procedures, it requires training and performance of initial procedures under supervision, once learnt, it is an easy, simple to apply and useful technique.
When compared to the cumulated cost of the long-term treatment of ß -thalassaemia, cost incurred on chorionic villous sampling and laboratory diagnosis of ß -thalassaemia mutation is negligible.
In cases where foetus was detected to be homozygous for ß -thalassaemia mutation, termination was done soon after the diagnosis, usually from 13-16th weeks of gestation. Termination of pregnancy was event free in all cases and no unusual complication was observed.
The babies detected to be heterozygous or normal, were all delivered normally, and remained well throughout infancy, pointing towards reliability of the diagnosis. Work has done to develop advanced and accessible protocols for non invasive prenatal diagnosis of genetic disease.25
Prenatal diagnosis of ß-thalassaemia in first trimester by chorionic villous sampling is a good tool for early detection of disease. Genetic counseling and prenatal diagnosis can prevent   ß -thalassaemia.26

Conclusion

Appropriate and extensive screening, accurate detection and counseling of at risk couples, along with antenatal diagnosis is a promising strategy for the reduction of mortality and morbidity from thalassaemia in countries where it is prevalent.  However, accomplishment of this goal necessitates detection of all couples at risk.  It is important to realize that prevention will be effective only if it is carried out uniformly for the entire population. Based on these results, it can be concluded that prenatal diagnosis of ß-thalassaemia for prevention can be done using chorionic villous sampling.

References

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