Flexibility of helix 2 in the human glutathione transferase P1-1. time-resolved fluorescence spectroscopy

Time-resolved fluorescence spectroscopy and site-directed mutagenesis have been used to probe the flexibility of alpha-helix 2 (residues 35-46) in the apo structure of the human glutathione transferase P1-1 (EC 2.5.1.18) as well as in the binary complex with the natural substrate glutathione. Trp-38, which resides on helix 2, has been exploited as an intrinsic fluorescent probe of the dynamics of this region. A Trp-28 mutant enzyme was studied in which the second tryptophan of glutathione transferase P1-1 is replaced by histidine. Time-resolved fluorescence data indicate that, in the absence of glutathione, the apoenzyme exists in at least two different families of conformational states. The first one (38% of the total population) corresponds to a number of slightly different conformations of helix 2, in which Trp-38 resides in a polar environment showing an average emission wavelength of 350 nm. The second one (62% of the total population) displays an emission centered at 320 nm, thus suggesting a quite apolar environment near Trp-38. The interconversion between these two conformations is much slower than 1 ns. In the presence of saturating glutathione concentrations, the equilibrium is shifted toward the apolar component, which is now 83% of the total population. The polar conformers, on the other hand, do not change their average decay lifetime, but the distribution becomes wider, indicating a slightly increased rigidity. These data suggest a central role of conformational transitions in the binding mechanism, and are consistent with NMR data (Nicotra, M., Paci, M., Sette, M., Oakley, A. J., Parker, M. W., Lo Bello, M., Caccuri, A. M., Federici, G., and Ricci, G. (1998) Biochemistry 37, 3020-3027) and pre-steady state kinetic experiments (Caccuri, A. M., Lo Bello, M., Nuccetelli, M., Nicotra, M., Rossi, P., Antonini, G., Federici, G., and Ricci, G. (1998) Biochemistry 37, 3028-3034) indicating the existence of a pre-complex in which GSH is not firmly bound to the active site.

HLA and complement factors alleles sharing in Italian couples with recurrent spontaneous abortions

Recurrent Spontaneous Abortion (RSA) is postulated to be due to several factors including immunogenetic mechanisms. Many studies have been conducted on the effect of the MHC region in the reproductive phenomena suggesting an immunological or genetic involvement in RSA. We studied couples with 3 or more abortions among a larger group of couples in which female partners were anti-cardiolipin antibodies negative, resulting in a population of 43 couples typed for HLA-A, B, C, DR, DQ. In 16 of these 43 couples, complement factors C4A, C4B, and Bf were typed. The data shows a statistically significant increase of C4B*Q0 in RSA patients (N = 32) compared with the control population (N = 44) (pc = .00147) and also a statistically significant increase of C4B*Q0 sharing in aborting couples (43.75%) against the expected sharing rate in the control population (1.86%) (p < .001). Frequency increase of C4B*Q0 allele in aborting population leads to the hypothesis that an imbalance of complement factors expression and activity can have detrimental effects on implantation and embryo survival. Additionally, the significant sharing rate of C4B*Q0 in couples with RSA could indicate the existence of a gene in linked to this allele predisposing to RSA and acting in a recessive manner if present in double copies in the fetus.

Adenosine deaminase and human reproduction: a comparative study of fertile women and women with recurrent spontaneous abortion

PROBLEM

We have investigated the possible role of adenosine deaminase (ADA) genetic polymorphism in human fertility through a comparative study of couples with recurrent spontaneous abortion (RSA) and healthy puerperae.

METHOD OF STUDY

Adenosine deaminase phenotype has been determined in 209 women with repeated episodes of unexplained spontaneous abortion (RSA) and their husbands, as well as in 115 healthy pregnant women from the population of Rome. An independent sample of 286 puerperae along with their newborn infants in the population of Penne was also studied.

RESULTS

The proportion of carriers of ADA*2 allele, which is associated with the lowest enzymatic activity, is lower among women with RSA than among healthy pregnant women from the same population of Rome. Preliminary observations suggest a protective effect of ADA*2 against the development of autoantibodies in RSA. Such an effect seems to be mediated by an interaction with AB0 blood groups. In the population of Penne the proportion of women carrying ADA*2 allele is higher among those who have had two or more previously born children than among women with only one or no children.

CONCLUSIONS

The data suggest that women carrying the ADA*2 allele are better protected against the spontaneous loss of embryos and have a higher fertility rate.

Solution structure of glutathione bound to human glutathione transferase P1-1: comparison of NMR measurements with the crystal structure

The conformation of the bound glutathione (GSH) in the active site of the human glutathione transferase P1-1 (EC 2.5.1.18) has been studied by transferred NOE measurements and compared with those obtained by X-ray diffraction data. Two-dimensional TRNOESY and TRROESY experiments have been performed under fast-exchange conditions. The family of GSH conformers, compatible with TRNOE distance constraints, shows a backbone structure very similar to the crystal model. Interesting differences have been found in the side chain regions. After restrained energy minimization of a representative NMR conformer in the active site, the sulfur atom is not found in hydrogen-bonding distance of the hydroxyl group of Tyr 7. This situation is similar to the one observed in an "atypical" crystal complex grown at low pH and low temperature. The NMR conformers display also a poorly defined structure of the glutamyl moiety, and the presence of an unexpected intermolecular NOE could indicate a different interaction of this substrate portion with the G-site. The NMR data seem to provide a snapshot of GSH in a precomplex where the GSH glutamyl end is bound in a different fashion. The existence of this precomplex is supported by pre-steady-state kinetic experiments [Caccuri, A. M., Lo Bello, M., Nuccetelli, M., Nicotra, M., Rossi, P., Antonini, G., Federici, G., and Ricci, G. (1998) Biochemistry 37, 3028-3034] and preliminary time-resolved fluorescence data.

Proton release upon glutathione binding to glutathione transferase P1-1: kinetic analysis of a multistep glutathione binding process

The fate of the thiol proton coming from the ionization of the sulfhydryl group of GSH in the active site of glutathione transferase P1-1 has been studied. pH changes caused by the binding of GSH to the enzyme in the absence of any inorganic buffer indicate that the thiol proton leaves the active site when the binary complex is formed. The amount of protons released is stoichiometric to the amount of GSH thiolate formed in the G-site. The apparent pKa value for the bound GSH, calculated with this potentiometric approach, is 6.18 +/- 0.09; very similar values are found by spectrophotometric (6.20 +/- 0.12) and by kinetic (6.00 +/- 0.08) experiments. Binding of S-hexylglutathione does not cause any proton release. Stopped-flow data obtained by means of an acid-base indicator show that the proton extrusion process (apparent t1/2 = 1.1 +/- 0.1 ms at 15 degrees C) is not rate limiting in turnover (apparent t1/2 = 34 +/- 4 ms at 15 degrees C). By comparing the kinetic behavior of three distinct events occurring during the binding of GSH to the enzyme, i. e., proton release, ionization of bound GSH and quenching of intrinsic fluorescence, it appears that the binding process follows a multistep mechanism possibly involving the conformational transition of a weak precomplex into the final Michaelis complex. This step is modulated by helix 2 motions and may be rate limiting at physiological GSH concentrations. These findings, coming from kinetic studies, are consistent with NMR data [Nicotra, M., Paci, M., Sette, M., Oakley, A. J., Parker, M. W., Lo Bello, M., Caccuri, A. M., Federici, G., and Ricci, G. (1998) Biochemistry 37, 3020-3027] and time-resolved fluorescence experiments [Stella, L., Caccuri, A. M., Rosato, N., Nicotra, M., Lo Bello, M., De Matteis, F., Mazzetti, A. P., Federici, G., and Ricci, G., manuscript in preparation].

The genetics of signal transduction and the feto-maternal relationship. A study of cytosolic low molecular weight phosphotyrosine phosphatase

Intracellular kinases mediate positive signalling from surface receptors by phosphorylating critical target proteins whereas phosphatases inhibit this process. Differential phosphatase activity at the feto-maternal interface could determine the appropriate relative growth and development on each side of the placenta. The highly polymorphic cytosolic low molecular weight phosphotyrosine-phosphatase (ACP1-cLMWPTPase) has been studied in 170 women who had at least two consecutive spontaneous abortions along with their husbands and in 352 normal puerperae along with their newborn babies. Symmetry analysis of joint wife/husband and mother/infant distribution suggests that when ACP1 activity is lower in the mother than in either her aborted fetus or her child, the probability of abortion is higher and the survival to term is lower as compared to pairs in which the ACP1 activity is higher in the mother than in her fetus. Further analysis has shown that the effect is due to S isoform: i.e. a high mother/fetus S isoform ratio favours intrauterine survival. Analysis of gestational duration and birth weight suggests that a high ACP1 maternal activity coupled with a low or moderate fetal activity favour fetal growth and developmental maturation. The present data indicate that maternal-fetal genetic differences in signal transduction could contribute significantly to variability of intrauterine developmental parameters and to pathological manifestation of pregnancy.

Catalytic mechanism and role of hydroxyl residues in the active site of theta class glutathione S-transferases. Investigation of Ser-9 and Tyr-113 in a glutathione S-transferase from the Australian sheep blowfly, Lucilia cuprina

Spectroscopic and kinetic studies have been performed on the Australian sheep blowfly Lucilia cuprina glutathione S-transferase (Lucilia GST; EC 2.5.1.18) to clarify its catalytic mechanism. Steady state kinetics of Lucilia GST are non-Michaelian, but the quite hyperbolic isothermic binding of GSH suggests that a steady state random sequential Bi Bi mechanism is consistent with the anomalous kinetics observed. The rate-limiting step of the reaction is a viscosity-dependent physical event, and stopped-flow experiments indicate that product release is rate-limiting. Spectroscopic and kinetic data demonstrate that Lucilia GST is able to lower the pKa of the bound GSH from 9.0 to about 6.5. Based on crystallographic suggestions, the role of two hydroxyl residues, Ser-9 and Tyr-113, has been investigated. Removal of the hydroxyl group of Ser-9 by site-directed mutagenesis raises the pKa of bound GSH to about 7.6, and a very low turnover number (about 0.5% of that of wild type) is observed. This inactivation may be explained by a strong contribution of the Ser-9 hydroxyl group to the productive binding of GSH and by an involvement in the stabilization of the ionized GSH. This serine residue is highly conserved in the Theta class GSTs, so the present findings may be applicable to all of the family members. Tyr-113 appears not to be essential for the GSH activation. Stopped-flow data indicate that removal of the hydroxyl group of Tyr-113 does not change the rate-limiting step of reaction but causes an increase of the rate constants of both the formation and release of the GSH conjugate. Tyr-113 resides on alpha-helix 4, and its hydroxyl group hydrogen bonds directly to the hydroxyl of Tyr-105. This would reduce the flexibility of a protein region that contributes to the electrophilic substrate binding site; segmental motion of alpha-helix 4 possibly modulates different aspects of the catalytic mechanism of the Lucilia GST.

Structural flexibility modulates the activity of human glutathione transferase P1-1. Role of helix 2 flexibility in the catalytic mechanism

Presteady-state and steady-state kinetic studies performed on human glutathione transferase P1-1 (EC 2.5.1.18) with 1-chloro-2, 4-dinitrobenzene as co-substrate indicate that the rate-determining step is a physical event that occurs after binding of the two substrates and before the final sigma-complex formation. It may be a structural transition involving the ternary complex. This event can be related to diffusion-controlled motions of protein portions as kcat degrees /kcat linearly increases by raising the relative viscosity of the solution. Similar viscosity dependence has been observed for Km GSH, while Km CDNB is independent. No change of the enzyme structure by viscosogen has been found by circular dichroism analysis. Thus, kcat and Km GSH seem to be related to the frequency and extent of enzyme structural motions modulated by viscosity. Interestingly, the reactivity of Cys-47 which can act as a probe for the flexibility of helix 2 is also modulated by viscosity. Its viscosity dependence parallels that observed for kcat and Km GSH, thereby suggesting a possible correlation between kcat, Km GSH, and diffusion-controlled motion of helix 2. The viscosity effect on the kinetic parameters of C47S and C47S/C101S mutants confirms the involvement of helix 2 motions in the modulation of Km GSH, whereas a similar role on kcat cannot be ascertained unequivocally. The flexibility of helix 2 modulates also the homotropic behavior of GSH in these mutants. Furthermore, fluorescence experiments support a structural motion of about 4 A occurring between helix 2 and helix 4 when GSH binds to the G-site.

Phosphotyrosine-protein-phosphatases and human reproduction: an association between low molecular weight acid phosphatase (ACP1) and spontaneous abortion

ACP1 (low molecular weight acid phosphatase) genetic polymorphism has been studied in 173 women with a history of two or more consecutive spontaneous abortions and in 1508 control subjects, including 482 normal pregnant women. The proportion of carriers of ACP1*C allele (*A/ *C, *B/*C) in women with a history of repeated spontaneous abortion is lower than in normal pregnant women and other control groups. Women with repeated spontaneous abortion show a specific decrease of ACP1 S isoform concentration as compared to normal pregnant women. The other component of ACP1 activity, the F isoform, does not show a significant difference between the two groups. The data suggest that women with ACP1 genotypes showing a high concentration of S isoform are relatively 'protected' against spontaneous abortion. Preliminary analysis of a sample of 352 normal puerperae along with their newborn babies supports this hypothesis.

Transvaginal sonography of the yolk sac in normal and abnormal pregnancy

A cross-sectional study comprising 117 consecutive first trimester singleton pregnancies was performed using transvaginal sonography (TVS) to evaluate size abnormalities of the secondary yolk sac (YS) vis-à-vis pregnancy outcome. In normal pregnancy outcome (NPO) the YS diameter showed an increase from the 5th to the 11th week, menstrual age, followed by a decrease and its disappearance after 12 weeks. A YS of abnormal size was statistically significant (p < 0.001) in spontaneous abortion (SA) versus NPO, with a sensitivity of 68.7%, a specificity of 99%, a positive predictive value of 91.6% and a negative predictive value of 95.2%. These preliminary results indicate that a measurement of the YS very early in gestation may be a useful marker of pregnancy outcome.

Interaction between ABO blood groups and ADA genetic polymorphism during intrauterine life. A comparative analysis of couples with habitual abortion and normal puerperae delivering a live-born infant

A total of 203 couples with unexplained habitual abortions and 364 consecutive normal puerperae along with their live-born babies were studied. The analysis of wife-husband joint ABO blood group distribution in couples with habitual abortion showed an excess of A incompatible mating type and a defect of B incompatible type as compared with expected proportions assuming random mating. The joint wife-husband ABO blood group distribution was further analysed in relation to the adenosine deaminase (ADA) genotype. A defect of O-A and A-O couples when the wife carries the ADA*1/*1 genotype and the husband carries the ADA*2 allele, and a defect of O-O and A-A when the wife carries the ADA*2 allele were observed. In the sample of normal puerperae, analysis of the joint mother-newborn ABO distribution in relation to the ADA genotype showed a pattern similar to that observed in couples with habitual abortion, i.e. there is a defect of O-A and A-O when the mother carries the ADA*1/*1 genotype and the newborn carries the ADA*2 allele and a defect of O-O and A-A types when the mother carries the ADA*2 allele. Altogether the data suggest an early loss of O-A and A-O zygotes when they carry the ADA*2 allele and an early loss of O-O and A-A zygotes when the mother carries the ADA*2 allele resulting in a deficit of these zygotic classes among both spontaneously aborted fetuses and live-born infants. The pattern of association observed in the mother-fetus type O-A (incompatible according to conventional terminology) appears similar to that observed for the reciprocal A-O type (compatible according to conventional terminology). Therefore strictly conventional immunological mechanisms cannot explain the whole pattern of associations. Cell to cell intereactions involving ABO antigens may have an important role at implantation: ADA, through the control of local adenosine concentration, could modulate these interactions influencing the probability of successful implantation.

A conformationally homogeneous combinatorial peptide library

In search for a rational way to convert the information encoded in peptide structures into peptidomimetics, major progress could be made by coupling the power of selection methods, now enormously increased in number as a result of the development of combinatorial peptide libraries, with the rational design of structure-inducing templates for the selectable sequences. The availability of libraries of peptides with predetermined structure would enable selection-driven peptidomimetic design, whereby a conformational model for the peptide pharmacophore would be directly derived from the screening, allowing the design of a suitable non-peptidic scaffold to replace the peptide backbone. We describe here the first example of a conformationally homogeneous combinatorial peptide library, which yields ligands with the expected structure upon selection. The library was built by randomising five positions in the alpha-helical portion of a 26 amino acid Cys2His2 consensus "zinc-finger" motif. Since in zinc-fingers metal coordination and folding are coupled, in our library metal-dependent binding represents a built-in control against the selection of structurally undefined sequences. The alpha-helical library was produced as both fusion with the pVIII protein of filamentous phage and soluble peptides by chemical synthesis, the latter enabling the expansion of the selectable repertoire by the inclusion of non-coded amino acids. The two libraries were independently screened with the same receptor (a monoclonal IgA reactive against the lipopolysaccharide of the human pathogen Shigella flexneri), yielding a very similar consensus. In particular, the peptides defined by both methods showed very strong, zinc-dependent binding to the IgA. The geometrical arrangement of the side-chains of the selected peptide pharmacophore was shown by circular dichroism, Co(II)-complex absorption and high-resolution NMR to be structurally invariant with respect to the parent zinc-finger.

[Psychosomatic sterility. Search for a hypothesis for personaity structure using Moretti's graphology method]

Over the past three years the authors have performed a random clinical study on couples who came to the aim of identifying the possible presence, in those cases in which it was not possible to pinpoint an organic or functional etiological factor, of a relationship between personality structure and so-called "sterility sine cause" which according to the recent studies by Pancheri and Zichella on reproductive emotionality, is thought to caused by a factor of psychosomatic origin, The substantiality of the concept of reproductive emotionality, otherwise referred to as sexual instinct, was put forward in 1962 by Padre Gerolamo Moretti, a leading figure of Italian graphology. Research to date, carried out using traditional methods of clinical psychology, interview and tests, in an attempt to determine a particular personality profile, has not produced completely satisfactory results. From the literature it does not appear that graphological analysis has been applied in research of this nature. Graphology, if used by competent and appropriately trained persons, is certainly a powerful and refined diagnostic method which enables an idiographic, holistic and integrated personality profile (intelligence and temperament) tp be obtained for the subject in question. Moretti's temperament classification was used to define the personality structure of patients: assault, resistance, assignment and expectation. Research using graphological techniques has revealed that it is possible to define a personality structure within which suspected "sine cause" patients may be classified. In comparison to the control group, there was a prevalent attitude expressing a tendency to reserve, introversion, diffidence, anxiety, excessive and sometimes unmotivated concern regarding persons and things, attachment to one's own ideas, inflexibility of one's own position, scarce capacity to make oneself available, excessive attention to formal aspects. A number of practical considerations also emerged from the research: the good level of acceptance and compliance with the diagnostic instrument used and the fact that the patient in question does not necessarily have to be present. Due to the ease of obtaining an example of the patient's handwriting, graphological analysis could be outinely requested as the first approach in suspected cases of sterility due to psychosomatic causes.

Blood levels of lipids, lipoperoxides, vitamin E and glutathione peroxidase in women with habitual abortion

Plasma levels of triglycerides, cholesterol, cholesterol esters, phospholipids, lipoperoxides, vitamin E and erythrocyte glutathione peroxidase activity showed no significant differences between 40 women with habitual abortion and controls. However, the levels of free fatty acids (FFA), which are extremely cytotoxic compounds, were significantly higher in women with habitual abortion (HA) than in controls (16.8 +/- 6.7 vs. 8.6 +/- 3.7 mg/100 ml, p < 0.01, respectively). The high amounts of FFA in HA women during pregnancy were probably due to a continuous and/or excessive stress-dependent discharge into the blood of catecholamines from autonomic nerve endings. These catecholamines can induce a strong uterine vasoconstriction and placental ischemia-hypoxia which, in association with additional insults caused by reoxygenation, might lead to eventual miscarriage.

Chromosome heteromorphisms and early recurrent abortions

In order to identify the role played by heterochromatic polymorphisms in miscarriage, an analysis was carried out on 257 couples, 137 of them with two or more abortions and 120 serving as a control. All couples were taken from two Italian populations: 77 cases and 70 controls came from an exogamic population whilst 60 cases and 50 controls came from an almost endogamic one. Out of the 137 cases, six couples in the exogamic and five in the endogamic groups were excluded because at least one partner had balanced chromosomal aberrations. Four controls from the exogamic group were also excluded for the same reason. The remaining 126 cases were analysed to detect the presence of chromosomal heteromorphism in one or both partners. The results suggested that chromosomal heteromorphism does not induce miscarriage. In fact, only one heteromorphism, inv(9)(p11q12), seems to be marginally related to recurrent abortion and only in the exogamic population. In addition no differences were found in the distribution of chromosomal heteromorphism in the couples analysed in relation to the number of abortions, i.e. two or more than two.

Purified FSH as a treatment for a cervical hostility

Abnormal cervical mucus (CM) quality and quantity is considered one of the causes of infertility which occurs in only 2 to 8 per cent of infertile couples. The periovulatory mucus with its specific properties is necessary to determine a correct Post Coital Test (PCT). Twenty patients, with infertility for over 18 months and with a baseline negative PCT (repeated at least three times) for abnormal CM, were treated with pFSH. Our results show that the pFSH improves the quality and quantity of CM in all for our patients including an improvement of penetration and motility spermatozoa in 55 per cent of our cases. Therefore we suggest the routine pFSH use in case of cervical hostility and recurrent negative PCT.

Treatment of malignant mesothelioma with epirubicin and ifosfamide: a phase II cooperative study

From May 1988 to March 1990, 17 consecutive patients with histologically proven malignant mesothelioma were treated with epirubicin 75 mg/sqm i.v. on day 1 and ifosfamide 1.8 gr/sqm/day i.v. from day 1-5. Treatment was repeated every 3 weeks until progression. Fifty-three chemotherapy cycles were administered to the 17 patients treated (median, 3 cycles/patient). No complete responses, 1 partial response, 8 stable diseases and 8 progressions were noted. Toxocity was acceptable and no treatment-related deaths occurred. Actuarial median survival was 6 months. In this study, a combination of full doses of epirubicin and ifosfamide did not prove to be active in malignant mesothelioma.

HLA-DR and DQ antigens and anticardiolipin antibodies in women with recurrent spontaneous abortions

IgG anticardiolipin antibodies (ACL) have been shown to occur in a high proportion of women with repeated unexplained miscarriages. Forty-nine women with unexplained recurrent spontaneous abortions (RSA), previously assayed for the presence of ACL by an enzyme-linked immunoabsorbent assay, were typed for HLA-DR and DQ antigens by the classical microlymphocytotoxicity test. Twenty-five women were positive for ACL and 24 were negative. HLA-DR7 was found in 24.5% of 49 habitually aborting women vs. 28% of healthy controls; but the DR7 frequency was 40% in ACL positive patients vs. 8.3% in ACL negative patients (P = 0.011). These results show that in the Italian population an association between HLA-DR7 antigen and ACL is present in women with unexplained RSA, suggesting that HLA-DR genes might control the susceptibility to specific autoantibody production.

Subclinical hypothyroidism and hyperprolactinemia

The authors have studied 25 women aged 22 to 26 years with a diagnosis of prolactinemia moderately increased in primary sterility. Among 25 women under observation, 7 (28%) showed a hormone picture of subclinic hypothyroidism. In fact the evaluation of TSH after stimulation with TRH showed a curve typical of the subclinic hypothyroidism. In 8 women (32%) the authors have found an increase of the thyroid gland, and in 3 patients (12%) galactorrhea. The increase of volume of the thyroid gland was constant in all the women with subclinic hypothyroidism. Considering the results obtained by this study, the authors point out a correlation between subclinic hypothyroidism-hyperprolactinemia and sterility. The data obtained are in accordance with that has been reported in literature.

Hysterosalpingographic abnormalities in infertile women: radiological and clinical interpretation

A review of 1035 hysterosalpingographies (HSG) has shown a frequency of acquired and congenital morphological alteration in 272 patients with spontaneous abortion and in 763 infertile couples. The frequency of congenital anomalies was 25.5% in spontaneous abortions and 5.3% in infertility. Acquired morphological anomalies were 11.7% in spontaneous abortion and 34.6% in infertility. Tubal problems represent 25% of lesions in infertility. Furthermore couples have been studied by correlating the male factor i.e. the sperm quality to various types of morphological anomalies observed in order to better evaluate the actual damage evidence by HSG.

Intrauterine death: an approach to the analysis of genetic heterogeneity

A study of survival time of zygotes in utero and the relationship with parental phenotype of a series of genetic polymorphisms was carried out in 41 couples with habitual abortion. Variability of intrauterine survival time was found to be much higher between families than within families suggesting that several genetic entities contribute to the condition clinically defined as habitual abortion. Significant differences of survival time were found in relation to the length of the paternal Y chromosome and to the maternal phenotypes of PGM1 and Ss. These observations are in line with previous data suggesting intrauterine selection in these polymorphisms. Further studies of the timing of intrauterine death in relation to 'normal' genetic polymorphisms may help to clarify the aetiology of spontaneous fetal loss.

Adenosine deaminase polymorphism. Associations at clinical level suggest a role in cell functions and immune reactions

It is well known that subjects homozygous for a rare silent allele of ADA may experience a severe combined immunodeficiency. By analogy we have investigated the possible relationship of normal ADA polymorphism with some situations, such as reproductive defects and fetomaternal interactions, in which immunological mechanisms may play an important role. A total of 572 consecutive newborns, 93 consecutive low birthweight infants, 46 couples with unexplained habitual abortion, and 24 couples with unexplained sterility were studied. The proportion of ADA 2-1 phenotype was reduced in couples with reproductive defects. In the sample of consecutive newborns the proportion of ABO incompatible babies was higher among ADA 2-1 than among ADA 1 types. ADA 2-1 phenotype was also associated with a reduction in the variability of gestational length. These associations were much more marked among male than among female babies. The proportion of ADA 2-1 was significantly lower in low birthweight infants than in the consecutively studied infants and normal adults. The present data suggest that biochemical variability resulting from the normal ADA polymorphism may be, at least in part, responsible for the variability of some immunological functions and related physiological variables and pathological conditions. They also provide evidence in favour of a selective advantage of ADA heterozygotes.