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Haemoglobinopathies constitute the commonest recessive monogenic disorders worldwide, and the treatment of affected individuals presents a substantial global disease burden. Carrier identification and prenatal diagnosis represent valuable procedures that identify couples at risk for having affected children, so that they can be offered options to have healthy offspring. Molecular diagnosis facilitates prenatal diagnosis and definitive diagnosis of carriers and patients (especially ‘atypical' cases who often have complex genotype interactions). However, the haemoglobin disorders are unique among all genetic diseases in that identification of carriers is preferable by haematological (biochemical) tests rather than DNA analysis. These Best Practice guidelines offer an overview of recommended strategies and methods for carrier identification and prenatal diagnosis of haemoglobinopathies, and emphasize the importance of appropriately applying and interpreting haematological tests in supporting the optimum application and evaluation of globin gene DNA analysis.

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A service for prenatal diagnosis of beta-thalassaemia was introduced in Pakistan in May 1994. Two renowned Islamic scholars, consulted before the service was introduced, ruled that a pregnancy can be terminated if the fetus is affected by a serious genetic disorder, and if termination is before 120 days (17 weeks) of gestation. During the first 3(1/2) years of the service 300 couples requested the test. Almost all the couples had been informed by their treating doctors. Most diagnoses were made between 10 and 16 weeks of gestation, and only 15 (5%) were reached after the 16th week. DNA analysis was by the amplification refractory mutation system (ARMS). A multiplex ARMS was developed in which three primer combinations identified the mutations in 91.5% of the couples. In 13 couples (4. 3%) linkage analysis was required for the fetal diagnosis. In 47/53 (88.7%) women carrying an affected fetus the pregnancy was terminated. In six cases it was declined principally on religious grounds. Postnatal confirmation of the prenatal diagnosis was possible in 117 unaffected children. One year after the start of the service, interviews with 141 couples with an affected child showed that 72% knew of the availability of prenatal diagnosis. Thirty-two of the informed couples had had a pregnancy, but only 18 (56%) used prenatal diagnosis. The main reasons for non-utilization of prenatal diagnosis were the cost of the test and fear of undergoing the test, though some gave no clear explanation. This study demonstrates that prenatal diagnosis is feasible and acceptable in a Muslim country such as Pakistan.

We have refined polymerase chain reaction (PCR) assays for the detection of sickle cell anaemia, the delta F 508 deletion causing cystic fibrosis, and the IVS1-110 mutation leading to beta thalassaemia, allowing them to be successfully performed upon single cells using fluorescent primers. We have also assessed the possibility of detecting aneuploidies of chromosomes 13, 18 and 21 using a quantitative fluorescent polymerase chain reaction (QF-PCR) with primers flanking polymorphic short tandem repeat (STR) markers. Trisomies were readily diagnosed by the detection of tri-allelic patterns. However some heterozygote normal and trisomic diallelic patterns did not produce the expected ratios of amplified PCR products due to preferential DNA sequence amplification. Total allelic drop out (ADO) did not occur with any of the cells tested. Multiplex QF-PCR assays can be performed on a single cell in under 6 h and simultaneously provide diagnosis of single gene defects, sex determination and an indication of selected chromosome aneuploidy.

We have refined polymerase chain reaction (PCR) assays for the detection of sickle cell anaemia, the delta F 508 deletion causing cystic fibrosis, and the IVS1-110 mutation leading to beta thalassaemia, allowing them to be successfully performed upon single cells using fluorescent primers. We have also assessed the possibility of detecting aneuploidies of chromosomes 13, 18 and 21 using a quantitative fluorescent polymerase chain reaction (QF-PCR) with primers flanking polymorphic short tandem repeat (STR) markers. Trisomies were readily diagnosed by the detection of tri-allelic patterns. However some heterozygote normal and trisomic diallelic patterns did not produce the expected ratios of amplified PCR products due to preferential DNA sequence amplification. Total allelic drop out (ADO) did not occur with any of the cells tested. Multiplex QF-PCR assays can be performed on a single cell in under 6 h and simultaneously provide diagnosis of single gene defects, sex determination and an indication of selected chromosome aneuploidy.

Samples of chorionic villi were obtained in the first trimester by aspiration using a cannula passed transcervically under the guidance of real time ultrasound. In initial studies in 47 anaesthetised patients immediately before therapeutic abortion a method was developed giving a success rate of 89%. In 10 patients successful sampling was performed as an outpatient procedure without anaesthesia. In all, seven diagnostic procedures were undertaken and four of the five unaffected pregnancies continued. The technique of chorionic villous sampling using real time ultrasound is simple to learn and yields material for biochemical analysis and chromosomal study without the need for tissue culture. The exact obstetric risk, however, remains to be defined.

Between 1979 and 1990, 170 couples at risk of having children with sickle cell disease, resident in the UK and with a continuing pregnancy, were referred for counselling at the University College Hospital Perinatal Centre. Approximately 50% of the couples, including those where one partner actually had sickle cell disease, requested prenatal diagnosis. This was requested in 82% of pregnancies when the mother was seen in the first trimester of pregnancy and in 49% when she was seen in the second trimester. More than 90% of referred couples who already had an affected child requested prenatal diagnosis. The type of sickle cell disease involved and ethnic group also influenced choice. These results show the importance of detecting and counselling couples at risk before pregnancy whenever possible. (J Med Genet 1992;29:820-3) rently, countrywide, 35 trained counsellors are working in 23 Health Authorities, 12 of them in six Health Authorities in North London (E Anionwu, personal communication). In England and the United States, about a third to a half of at risk couples counselled by a trained person request prenatal diagnosis.78 This suggests that a review of a series of cases may cast light on factors that influence the choices informed couples make. Here we report the results of a review of the records of pregnant women at risk for having children with sickle cell disease counselled at the UCH Perinatal Centre, which offers a regional and national service for prenatal diagnosis of haemoglobin disorders. The results show that choice is influenced by the nature of the genetic risk, ethnic group, experience of an affected family member, and the possibility of diagnosis in the first trimester of pregnancy. Clearly, couples at risk for having children with inherited diseases should be identified and provided with expert counselling either before or at the earliest possible stage of pregnancy.