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This paper reviews the molecular pathology of a heterogeneous group of beta-thalassemia heterozygotes which may be referred to as atypical beta-thalassemia. This group includes four different categories of heterozygous beta-thalassemia, which are characterized, respectively, by (1) normal MCV and MCH; (2) normal Hb A2; (3) normal MCV, MCH, and Hb A2 and imbalanced globin chain synthesis only or, (4) the presence of clinical manifestations. The first group is represented by a limited proportion of double heterozygotes for alpha- and beta-thalassemia. The second group includes two categories. One category is double heterozygotes for delta- and beta-thalassemia with the delta-thalassemia mutation in cis or in trans to beta-thalassemia. A number of delta-thalassemia mutations which produce this phenotype by interacting with beta-thalassemia have been described. The other category within the second group is heterozygotes for some mild beta(+)-thalassemia mutations. Within the third group, conclusive evidence for a mutation within the beta-globin gene cluster producing the silent beta-thalassemia phenotype has been obtained solely for a C----T substitution at -101 within the CACCC box of the beta-globin gene. Possible candidates are the complex rearrangements (-T, +ATA; -T, +ATATA) found at position -530 from the cap site. In the group of thalassemic hemoglobinopathies, a series of mutations mostly located in the third exon and producing elongated or truncated molecules have been recently reported. Most of the mutations are silent at the protein level, produce inclusion bodies in peripheral erythrocytes, and show a dominant transmission pattern or occur sporadically.

Nomifensine, an antidepressant agent which activates dopamine (D) neurotransmission mainly by inhibiting DA reuptake in the central nervous system, was administered either to puerperal lactating women or to subjects with nonpuerperal hyperprolactinemia. In 10 postpartum women and in 7 women with no evidence of PRL-secreting tumor, oral administration of nomifensine (100 or 200 mg, respectively) induced in the following 5 h a clear-cut inhibition of plasma PRL levels; in 10 patients with PRL-secreting tumors, the drug did not lower plasma PRL levels. In 2 of these patients nonsupressibility of plasma PRL levels to nomifensine was the only indication of the existence of a pituitary microadenoma. It is proposed that acute nomifensine testing may be a valid neuropharmacological tool for discriminating between individuals with and without pituitary adenoma.

In women with physiological puerperal hyperprolactinaemia, acute administration of Piribedil (100 mg po), a drug which stimulates dopamine receptor sites, was as effective as that of 2-Br-alpha-ergocryptine (CB 154, 5 mg po) in suppressing the elevated baseline plasma prolactin (PRL) levels. In two hyperprolactinaemic women with radiological evidence of an intrasellar pituitary tumour, Piribedil (100 mg po), in contrast to CB 154 (5 mg po), failed to modify plasma PRL levels, whereas in 3 other hyperprolactinaemic women with no radiological evidence of pituitary tumour, its effect was not clear-cut, even though it could not be differentiated from that of CB 154. These results indicate that Piribedil is an effective suppressor of plasma PRL levels in the human and suggest that its action is more evident in puerperal than in pathological hyperprolactinaemia.

Electroretinography, a simple, bloodless technique commonly used in ophthalmological diagnostic practice, seems to give important informations on the level of activity of the retinal and/or other central dopaminergic systems. The Authors have employed this technique in a group of 30 normal pregnant women in the ninth month of gestation, in order to evaluate the dopaminergic activity in a condition of physiological hyperprolactinemia, such as pregnancy, and in a group of 25 normal nonpregnant control women. The b wave amplitude of the electroretinographic traces was significantly higher in pregnant women than in controls, suggesting an over-activity of dopaminergic systems in late pregnancy. The possible interpretations of these data are discussed.

The Authors studied the behaviour of anticomplement and heparin-like activities in human term placentas in relation to intrauterine fetal growth retardation. These two biological activities might be involved in regulatory mechanisms of great importance for the fetal growth. The anticomplement activity was significantly lower in IUGR placentas than in controls, while no change was found in heparin-like activity. The decrease of anticomplement activity might be associated to immunological mechanisms, possibly related to a placental microcirculation damage, with consequent fetal growth retardation. For what concerns HCS and E3 plasma levels during pregnancy, a significant reduction of HCS in IUGR subjects was observed, confirming a decreased functional activity of placenta. The E3 levels, on the contrary, were slightly, but not significantly lower in IUGR patients.

In this review, we have described the molecular bases accounting for beta, delta beta and gamma delta beta-thalassemias, discussed the molecular mechanisms responsible for the production of mild forms of thalassemia and presented a strategy for detecting beta-thalassemia mutations in each at risk population. The molecular bases of beta-thalassemia are very heterogeneous. The great majority of beta-thalassemias are caused by point mutations affecting the coding region or critical areas of the beta-globin gene and are only rarely produced by gross gene rearrangements. By contrast delta beta and gamma delta beta-thalassemias most commonly result from gross gene deletion. Determinants recognized to date as able to produce mild forms of beta-thalassemias, are beta-thalassemia mutations with a high residual output of beta-globin chain production, coinheritance of alpha-thalassemia or nondeletion HPFH linked or not linked to the beta-globin gene cluster, delta beta thalassemias and specific beta-globin haplotype. Because in each population a restricted number of molecular defect occurs, strategies have been developed to detect the beta-thalassemia mutations in prospective parents in each at risk population. These strategies are based on the direct detection of the mutation by dot blot analysis on enzymatically amplified DNA using a limited number of oligonucleotide probes complementary to the most common mutations in each population.