Vivian Chan

Genetic and clinical features of hemoglobin H disease in Chinese patients

BACKGROUND Normally, one pair of each of the two alpha-globin genes, alpha1 and alpha2, resides on each copy of chromosome 16. In hemoglobin H disease, three of these four alpha-globin genes are affected by a deletion, a mutation, or both. We studied the alpha1-globin gene abnormalities and the clinical and hematologic features of Chinese patients with hemoglobin H disease in Hong Kong. METHODS We assessed the clinical features, hematologic values, serum ferritin levels, and liver function of 114 patients with hemoglobin H disease. We also performed echocardiography and magnetic resonance imaging of the liver and examined the two pairs of alpha-globin genes. RESULTS Hemoglobin H disease in 87 of the 114 patients (76 percent) was due to the deletion of three of the four alpha-globin genes (--/-alpha), a combination termed the deletional type of hemoglobin H. The remaining 27 patients (24 percent) had the nondeletional type of hemoglobin H disease, in which two alpha-globin genes are deleted and a third is mutated (--/alphaalphaT). All 87 patients with the deletional type of hemoglobin H were double heterozygotes in whom there was a deletion of both alpha-globin genes from one chromosome, plus a deletion of the alpha1 or alpha2 gene from the other chromosome (--/alpha- or --/-alpha). A variety of mutated alpha-globin genes was found in the patients with nondeletional type of hemoglobin H disease. Patients with the nondeletional type of the H disease had more symptoms at a younger age, more severe hemolytic anemia, and larger spleens and were more likely to require transfusions than patients with deletional hemoglobin H disease. The severity of iron overload was not related to the genotype. CONCLUSIONS Chinese patients in Hong Kong with the nondeletional type of hemoglobin H disease have more severe disease than those with the deletional type of the disease. Iron overload is a major cause of disability in both forms of the disease.

EFFECT OF SURGICAL STRESS ON PITUITARY‐TESTICULAR FUNCTION

The effect of surgical stress on the secretions of LH, FSH, testosterone (T) and oestradiol (E2) were studied in twelve male patients. During surgery LH rose significantly; post‐operatively, LH fell but remained persistently elevated a week after operation. However, T and E2 fell progressively to a nadir on the second and fifth post‐operative day respectively and remained suppressed. Serum FSH showed no significant change. Despite a post‐operative decrease in sex hormone binding globulin (SHBG) binding capacity, non‐SHBG bound T showed a decrease parallel to T. Multiple sampling studies showed that the secretions of LH were increased and that of T were decreased post‐operatively. Following surgery, LH responses to LHRH were magnified, FSH and T responses showed no significant change when compared with the pre‐operative responses. These data suggest that secretions of LH were increased during surgery. Following surgical stress, T and E2 concentrations were suppressed resulting in a compensatory elevation of LH concentrations.

Consistent Patterns of Allelic Loss in Natural Killer Cell Lymphoma

Natural killer (NK) cell lymphomas are a group of rare but highly aggressive malignancies. Clinically, they can be divided into nasal NK cell lymphomas, nonnasal NK cell lymphomas, and aggressive NK cell lymphoma/leukemia. To determine the patterns of genetic deletions in these tumors, we performed loss of heterozygosity (LOH) analysis on 15 cases (11 nasal and four nonnasal), and fluorescence in situ hybridization on three cases of aggressive lymphoma/leukemia. A panel of 41 microsatellite loci on chromosomes 6q, 11q, 13q, and 17p were investigated. LOH at chromosomes 6q and 13q was frequently detected in NK cell lymphomas, being found in 80 and 66.7% of cases, respectively. LOH at chromosomes 11q and 17p was less common, being found in 28.6 and 30.8% of cases, respectively. Most tumors showed multiple loci deletions at different chromosomal regions, but several patterns of LOH could be defined. LOH at chromosome 6q was found in 90.9% of nasal NK cell lymphomas, but only in 50% of nonnasal NK cell lymphomas. LOH at chromosome 13q was found in 63.6% of nasal NK cell lymphomas and 75% of nonnasal NK cell lymphomas. For nasal NK cell lymphomas, LOH at 13q was found in 33.3% of cases at presentation, but 100% of cases at relapse. Five tumors showed LOH in only one chromosomal region, involving 6q in three cases (two nasal and one nonnasal), and 13q in two cases (both nonnasal). For the three cases of aggressive NK cell lymphoma/leukemia studied by fluorescence in situ hybridization, DNA loss at 13q14 and 17p13 regions were demonstrated. 17p13 seemed to be more commonly involved in aggressive than nasal and nonnasal NK cell lymphomas. Our results suggested that consistent patterns of LOH could be defined in NK cell malignancies. These deleted loci may contain genes important in the initiation and progression of this lymphoma.

EFFECT OF ACUTE MYOCARDIAL INFARCTION ON PITUITARY‐TESTICULAR FUNCTION

The effect of acute myocardial infarction on the secretions of LH, FSH and testosterone was studied in thirteen male patients. Plasma testosterone fell transiently on the fourth day after acute myocardial infarction. This was accompanied by a rise in LH on the same day which persisted for a week after infarction. Serum FSH showed no significant change. The data suggest that following the medical stress of myocardial infarction, testosterone concentration was suppressed resulting in a compensatory rise in LH.

Molecular defects in Hb H hydrops fetalis

The molecular defect in two unique cases of Hb H hydrops fetalis has been characterized. Both cases are due to co‐inheritance of a ‘non‐deletion’ defect affecting the α2 gene: at codon 30 (ΔGAG, Glu) and codon 59 (G  →  A, Gly →  Asp) respectively, and a ζ‐α thalassaemia (thal) 1 or α thal 1 genotype. These two non‐deletion defects, unlike previously described cases, resulted in severe anaemia of the fetuses and emphasize the importance of performing prenatal diagnosis for these families.

A reverse dot-blot method for rapid detection of non-deletion α thalassaemia

A reverse dot blot method based on membrane‐bound allele‐specific oligonucleotides as hybridization targets for amplified α‐gene fragments has been developed for the rapid detection of four non‐deletion α thalassaemia defects found in the Chinese. Since these non‐deletion defects account for 22.8% of haemoglobin H disease, a sensitive, specific and rapid screening method should be of value.

Deep Vein Thrombosis and Changes in Coagulation and Fibrinolysis after Gynaecological Operations in Chinese: the Effect of Oral Contraceptives and Malignant Disease

Of 154 Chinese patients who underwent gynaecological operations, four showed a positive 125I fibrinogen leg scan for venous thrombosis, an overall incidence of 2.6%. In those who were on oral contraceptives and had major pelvic surgery for benign conditions, the incidence was 10.5%; in those who had Wertheim hysterectomy for carcinoma of cervix, it was 6.7%. This confirms the rarity of post‐operative thromboembolism in the Chinese. Fragment E showed a biphasic rise after major operation due to tissue injury and venous thrombosis. In patients with malignancy, the postoperative ‘fibrinolytic shutdown’, represented by decreased plasminogen activator together with increased α1, antitrypsin and C inhibitor levels, was more marked. In addition, α2 macroglobulin level was lower and fell significantly after operation. In patients on oral contraceptives, fragment E levels were higher after surgery and there was no decrease in plasminogen activator levels. Antithrombin III levels did not fall except in three of the four patients with venous thrombosis. A marked increase in fragment E level and a decrease in antithrombin III level might be useful diagnostic markers for postoperative venous thrombosis.

TRANSFER OF DIGOXIN ACROSS THE PLACENTA AND INTO BREAST MILK

Eleven mothers given digoxin throughout pregnancy because of rheumatic heart disease were studied. Digoxin was identified in the placenta and, for the first time, in milk. Paired cord and maternal blood samples obtained at parturition showed lower digoxin levels in cord blood than in maternal blood. The total tissue‐bound digoxin level in the placenta correlated closely with maternal digoxin levels. These findings suggest strongly the presence of a placental barrier for digoxin. Similar digoxin concentrations (0·825±0·015 nmol/l) were found in milk samples obtained daily between the third and seventh days postpartum. The half‐life of digoxin in the newborn was 36·2±5·43 hours (Mean±SEM); thus all the digoxin present at birth would be excreted within 10 to 11 days.

Use of the polymerase chain reaction in the detection of AML1/ETO fusion transcript in t(8;21)

Background. t(8;21)(q22;q22), found in acute myeloid leukemia (AML) and occasionally in myelodysplasia (MDS), results in the fusion of the AML1 gene on 22q22 to the ETO gene on 8q22, generating a chimeric AML1/ETO transcript, which is a molecular marker of the translocation.

A thalassaemia array for Southeast Asia

The α and β thalassaemias are the commonest genetic disorders worldwide. The homozygous state is associated with high morbidity and mortality, thus screening of at‐risk pregnancies and prenatal testing are strongly advocated. A thalassaemia (thal) array has been designed using allele‐specific arrayed primer extension (AS‐APEX) for the simultaneous analysis of 15 non‐deletion α‐gene defects and 23 β‐gene mutations commonly found in southeast Asian countries, where thalassaemias are highly prevalent. This overcomes the problem of using multiple reverse dot blot analysis. The array showed 100% sensitivity and specificity in the detection of 120 β‐thal mutants and 35 non‐deletion α‐thal mutants. It is robust enough to be produced in a single place and shipped to other laboratories for use. The production cost of the array is low, each slide can be used for three different test samples and is therefore amenable to large scale antenatal screening in southeast Asian countries.