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The fragile X syndrome is the most common inherited form of mental retardation. Its prevalence is estimated to be one in 1000-4000 males and one in 2000-6000 females, depending of the region. A large canadian population study in Quebec has shown a frequency of 1/260 carrier women. The fragile X syndrome was the first disease shown to be associated with "dynamic mutations", caused by an amplification of an unstable DNA sequence transmitted from generations to generations till a pathologic expression: mental retardation. The prevention is possible by a specific DNA analysis of patients and male and female carriers. It is possible to detect the mutation or the premutation in pregnant women and to propose a prenatal diagnosis by molecular study on chorionic villi samples or cultivated amniocytes.

In order to investigate the origin of mutations responsible for the fragile X syndrome, two polymorphic CA repeats, one at 10 kb (FRAXAC2) and the other at 150 kb (DXS548) from the mutation target, were analyzed in normal and fragile X chromosomes. Contrary to observations made in myotonic dystrophy, fragile X mutations were not strongly associated with a single allele at the marker loci. However, significant differences in allelic and haplotypic distributions were observed between normal and fragile X chromosomes, indicating that a limited number of primary events may have been at the origin of most present-day fragile X chromosomes in Caucasian populations. We propose a putative scheme with six founder chromosomes from which most of the observed fragile X–linked haplotypes can be derived directly or by a single event at one of the marker loci, either a change of one repeat unit or a recombination between DXS548 and the mutation target. Such founder chromosomes may have carried a number of CGG repeats in an upper-normal range, from which recurrent multistep expansion mutations have arisen.

Thirty-seven pregnancies at risk for Niemann-Pick type C disease were monitored by study of cultured amniotic fluid cells (8 cases) or chorionic villus cells (29 cases) in 23 couples over the period 1984–91. An early protocol combined determination of sphingomyelinase activity with electron microscopy. The current strategy, based on the demonstration of specific abnormalities in intracellular processing of exogenous cholesterol, combines the study of the early phase (first 6 h) of LDL-induced cholesteryl ester formation and the histochemical evaluation (filipin staining after 24 h of LDL uptake) of the LDL-induced accumulation of unesterified cholesterol. Thirteen fetuses were predicted to be affected. Confirmation of the diagnosis was made by study of cholesterol processing in fetal skin fibroblast cultures and/or by demonstration of a characteristic lipid storage in fetal liver, already present at 14 w gestation. Definition of the biochemical phenotype (classical, variant, or intermediate) of the index case, with regard to cholesterol-processing abnormalities, is an absolute prerequisite to adequate genetic counseling in a given family. Prenatal diagnosis has now proved a safe procedure in the predominant (approximately 85%) group of families with the classical phenotype.

Having seen 87 cases we will now attempt to refine the management to be carried out when intra-abdominal hyperechogenic masses are found in the fetus. Before the 20th week of amenorrhoea (47 cases) amniocentesis can be used to study the digestive enzymes to determine the fetal karyotype. The normal results for intestinal enzymes makes it possible to rule out fetal cystic fibrosis. Three karyotype abnormalities were found in this series. After the 20th week (40 cases) intestinal enzymes cannot be interpreted. The diagnosis of cystic fibrosis then must rely on Delta F 508 mutation; but the absence of this mutation does not exclude cystic fibrosis. When ultrasound signs of intra-abdominal hyper-echogenicity are found the diagnosis of cystic fibrosis should not be thought of first, because in this series the majority of fetuses who had this sign were born without any malformation. Four cases of cystic fibrosis that were confirmed have been found but equally there were other serious malformations, three chromosome abnormalities, four intestinal atresias, ten unexplained intra-uterine deaths and one case of biliary duct atresia.

Correlations have been established between phenotype and karyotype in spontaneously aborted specimens. The criteria used to determine the phenotype were based on estimated developmental age and macroscopic examination of embryo and placenta, taking into account the morphological modifications due to in utero retention. The probability that a chromosomal aberration was the cause of the abortion is high when the developmental arrest occurred before 5-6 weeks and the expulsion was delayed. The frequency could be estimated at 75% when the developmental arrest was at 2-3 weeks, and 65% when the developmental stage reached 5-6 weeks. Main anatomical features are described permitting an attempt to assign the type of chromosomal anomaly by ultrasonographic examination.

The amniotic fluid activity of gamma glutamyl transpeptidase (GGT), leucine aminopeptidase (LAP) and alcaline phosphatase (AP) and disacharidases was examined in 66 pregnancies with the risk of cystic fibrosis (CF) in the 17th-21st weeks of gestation. So far 28 pregnancies continue. The prenatal diagnosis was confirmed in all so far delivered children or aborted foetuses if the GGT activity was higher than 400 U/1 (10th percentile) or lower than 190 U/1 (3rd percentile) in the 17th-18th weeks. The results of other microvillar and ultrasound examinations were consistent with it. From 3 pregnancies with GGT activity in the range of 3-5 percentiles and abnormal activities of other microvillar enzymes, the CF was confirmed only in one aborted foetus with meconium ileus and with abnormal ultrasound examination. In other 2 pregnancies with normal ultrasound, healthy children were delivered. In 3 pregnancies with the GGT in the range of 5-10 percentiles and abnormal other microvillar enzymes, one false negative GGT and ultrasound examination was disclosed. The other 2 aborted foetuses did not exhibit the signs of CF in necropsy examinations. The meconium ileus was found in 2/4 of aborted foetuses with GGT lower than 3 percentiles, abnormal activities of other microvillar enzymes and abnormal ultrasound examination. The ultrasound examination was correct in 2/10 of pregnancies with GGT lower than 3 percentiles or abnormal activities of other microvillar enzymes. The GGT examination in 19th-21st weeks provided similarly reliable diagnostic results. The importance of fetal karyotyping and ultrasound elimination of other severe congenital anomalies is pointed out for critical interpretation of microvillar enzyme activities testing.(ABSTRACT TRUNCATED AT 250 WORDS)

The fragile-X mental retardation syndrome, one of the most prevalent chromosome X-linked diseases (approximately equal to 1 of 2000 newborn males), is characterized by the presence in affected males and in a portion of carrier females of a fragile site at chromosomes band Xq27. We have performed a linkage analysis in 16 families between the locus for the fragile-X syndrome, FRAXQ27, and two polymorphic DNA markers that correspond to the anonymous probe St14 and to the coagulation factor IX gene F9. Our results indicate that the order of loci is centromere-F9-FRAXQ27-St14-Xqter. The estimate of the recombination fraction for the linkage F9-FRAXQ27 is 0.12 (90% confidence limits: 0.044-0.225) and 0.10 for FRAXQ27-St14 (90% confidence limits: 0.040-0.185). Recombination between St14 and F9 does not appear to be significantly different in normal and fragile-X families. The two flanking probes were used for diagnosis of the carrier state and for detection of transmission of the disease through phenotypically normal males. They should also allow first-trimester diagnosis with a reliability of about 98% in 40% of the families. Used in conjunction with the cytogenetic analysis, the segregation studies with both probes should improve the genetic counseling for the fragile-X syndrome and should be useful for the formal genetic analysis of this unique disease.

A pericentric inversion of chromosome 9 has been detected in 10 unrelated families. The break points are identical and the inversions involved the heterochromatic segment. The effects of inversion of chromosome 9 on different aspects of reproductive failure are discussed.

The analysis of DNA repair processes is described in two pregnancies at risk for xeroderma pigmentosum. In both cases, excision repair (measured by unscheduled DNA synthesis) and postreplication repair were analyzed. An affected and an unaffected fetus were identified within 3 weeks after amniocentesis. The cells from the affected fetus were found to be deficient in excision DNA repair, whereas the PRR patterns were intermediate between those of normal and PRR deficient cells. This indicates the possibility of prenatal diagnosis of PRR deficient XP patients (XP variants).

Associations of the three n degrees 18 chromosomes were studied in a trisomy 18 fetus (the chromosomal constitution of which had been identified by amniocentesis). The three classes of associations observed were those observed in other trisomic organisms:trivalent, trivalent presenting an important asynaptic region, and bivalent accompanied by a univalent. In addition, the sequence was established of chromomeres, the number of which varied from 18 to 23 depending on the degree of chromosome contraction. In elongated pachytene oocyte bivalents each G-band of mitotic metaphase chromosomes could be subdivided into several sub-bands.

Antenatal diagnosis enables certain fetal abnormalities to be detected "in utero", and in particular mongolism. This examination is often undertaken in the process of medical attention in pregnancy. This explains why interviews with pregnant women about this far from ordinary act have become so superficial. Men and women react differently to this take-over. The former take part in a scientific discussion, the latter, who are more closely involved, which is to say with their whole bodies, set themselves against both good and bad doctors and often try to resist this test. We have attempted to understand the meaning of wanting to or not wanting to know the sex of the child in this context before its birth, and what happens to the wish to have a child after this kind of medical care.

Twenty-eight HLA-A and B markers have been tested in 49 couples who had one or more triploid abortions. The antigen frequencies were compared to those of 209 couples and 591 normal individuals as controls. No significant deviations were observed. However, a non significant excess of antigens shared in common by both parents was shown in comparison with the normal couples. This could be related to a possible dispermy mechanism. On the other hand, a slight excess of A 28 may be in relation to a possible anomaly of gametogenesis.

Chorionic villi biopsy allows first trimester prenatal diagnosis of some genetic diseases. In this study the results of 163 diagnoses are presented, and among these, 59 diagnoses of autosomal recessive metabolic diseases with 8 observations of congenital adrenal hyperplasia due to 21 OH deficiency and 6 observations of Fanconi anemia.

Cholinesterase electrophoresis was performed in 802 amniotic fluids and its value in the detection of neural tube defects was compared with those of ultrasonography and amniotic fluid alpha-foetoprotein levels. Cholinesterase electrophoresis confirmed the ultrasonic diagnosis in 51 cases of neural tube abnormality and made it possible to diagnose neural tube defect in 6 other cases which had remained undetected by ultrasound and by alpha-foetoprotein level measurements. When our technique is used before the 28th week of gestation, false-positive results concern abnormalities which are easily detected by ultrasound (omphalocele, Bonnevie-Ullrich syndrome, sacrococcygeal tumour). We did not observe any false-negative result.

Determination of HLA antigens can be used for prenatal diagnosis of some congenital anomalies such as adrenal hyperplasia (21-hydroxylase deficiency). This necessitates rigourous HLA typing of fetal cells cultivated in vitro. The method we have developed utilizes microcytotoxicity and quantitative microabsorption tests which have been adapted to the types of cells found in these cultures.

Banding technique were applied to cell lines which had been established earlier from spontaneous human abortions and preserved frozen. Most of the autosomes were shown to be involved in lethal trisomies. As a result of the precise identification of affected chromosomes, the exact time of developmental arrest as well as certain phenotypes could be correlated with the various trisomies.

Some multisystemic abnormalities associations which can be found by ultrasound examination are sometimes chromosome anomalies and amniocentesis must be performed for confirmation. By ultrasonography we can now reach a new objective element: the fetus extremities. Limbs anomalies, such as polydactily, club-feet and/or club-hands must lead to perform amniocentesis in order to assess or not a possible 13 or 18 trisomy.

Various cytogenetic studies of early spontaneous abortions have observed trisomy 21 in about 3% of the abortuses. Analyses of prenatal diagnosis performed during the 17th week of gestation and observations on late spontaneous abortions and perinatal deaths have also shown the importance of lethal trisomy 21 in the second half of pregnancy. From these studies, it can be estimated that at least four-fifths of conceptuses with trisomy 21 fail to survive. One important question is why the same chromosome anomaly in a zygote can lead either to an early arrest of development or to a liveborn infant. Pathologic examinations of spontaneously aborted embryos with trisomy 21 have rarely shown malformations that can explain the death of the embryo, but macroscopic and microscopic examinations of their placentas show growth retardation and hypoplasia. Analysis of in vitro growth characteristics of cell lines established from tissues of trisomy 21 embryos have demonstrated differences in cell population doubling times; this may explain variations in the developmental potentials of conceptuses with trisomy 21.

In diagnosing and preventing the birth of abnormal children the authors stress the necessity of team work of different specialists and their centralisation at the University complex or hospitals. The results of such a team work organised at the Division of Medical Genetics, Department of Gynecology and Obstetrics in Ljubljana and their experience in detecting some of monogenic, chromosome, and etiologically unknown disorders are presented, as well as the results of the follow-up of certain cases. The value of team work in genetic counselling is also pointed out.

Genetic, clinic and biologic features from three families with Xq fra syndrome are described. First, the authors give their experience for the best ways of culture in order to see the fragile site. Then, they insist upon the main points of each family: in the first, two women have a mental retardation; in the second, a prenatal diagnosis could be made; in the third, treatment with folic acid did not change the IQ but improves the behaviour of two brothers.

Four unexpected karyotypes were found in prenatal diagnosis: 47,XXX; 47,XXY; double reciprocal translocation; Yq-. Supplementary biological studies (including specific Y-DNA probes) are carried out in order to help in the parents' decision. No induced abortion was performed. The children are described after delivery.

Children with trisomy 21 are only a part of conceptuses with this anomaly which leads mainly to early arrests of development. Growth retardation of embryo and placenta are the main characteristics of these abortuses. Cell lines were established from tissues of trisomics 21 of different types of evolution (early spontaneous abortions, abortions after prenatal diagnosis, stillbirths and newborn-infants). Differences in the in vitro growth characteristics of these cells have been evidenced. They may explain the variations in the developmental potentials of trisomy 21 conceptuses.

The close genetic linkage between 21 hydroxylase deficiency and HLA loci considerably enlarges the possibilities of genetic counselling. Two 21-OH deficient complex families are reported, illustrating several aspects of this genetic counselling: detection of carriers, determination of the actual risk to related couples, suspicion of 21-OH deficiency by an HLA specificity association, and prenatal diagnosis.

The request for prenatal diagnosis of cystic fibrosis has been evaluated by an interview during a visit at a cystic fibrosis clinic among 32 couples whose one or several children are affected. Six couples resorted to the procedure between June 1984 and October 1985. In all the cases, in these families the only child (or children) alive was affected. The diagnosis of the disease in the first affected child reduces the number of children planned by the family. The significant use of the test, since its availability points to the existence of a real demand from the parents.

In cases of artificial insemination for genetic indication, it may be useful to determine that in fact the foetus is the result of AID. Chromosome markers may or may not provide an answer, when HLA typing of amniotic fluid cells can.

We have monitored 3 pregnancies at risk for galactosemia by deficiency in Galactose-1-Phospho uridyl transferase. Galactosemia was diagnosed in the 1st case; heterozygoty in the 2nd, and a "double heterozygoty" in the 3rd. The latter is the first example of such a diagnosis. Post natal confirmation was obtained in the three cases. Arguments are given for the usefulness of this prenatal diagnosis.

A dose genetic linkage exist between the HLA complex (especially HLA-B), and the 21 hydroxylase deficiency form of adrenal hyperplasia. By their polymorphisms HLA antigens can be used as "markers" to follow the segregation of 21-OH deficiency in families, to diagnose the heterozygous offspring and eventually to offer a prenatal diagnosis to couples at risk. In late onset forms of 21-OH deficiency the same genetic linkage has been demonstrated with a high frequency of HLA-B14 antigen.

The results confirmed the fiability and the accuracy of the different acts and technics leading to these diagnosis. A prospective study of the safety of amniocentesis involved more than 1000 subjects. The analysis of the information on the pregnancy, the delivery, the state at birth and after birth of the infant did not show any significant increase of pathologic findings which may be related to immediate or delayed consequences of amniocentesis.

Etiological and epidemiological studies of triploid and hydatidiform molar conceptuses were done using HLA polymorphism. The segregation of HLA markers allowed to know the etiology of 25 triploidies and 19 hydatidiform moles. Five other moles and a post molar choriocarcinoma were also studied by molecular hybridization. This confirms that triploidies in about 3/4 of the cases involved two sets of paternal chromosomes mainly by di-sperm. Hydatidiform moles from Algeria, France and Senegal were all of androgenic origin excepted for one case. DNA analysis of the choriocarcinoma demonstrated the presence of a paternal marker suggesting for this case a direct cellular lineage from the mole. Positive associations with HLA A 28 and B 7 were found which could be related to gametogenesis-fecundation dysfunction. A slight excess of antigens shared by parents of triploidies was shown. This was not observed for parents of hydatidiform moles but when they shared HLA antigens a preferential inheritance in the mole of the shared specificities was observed. This relative compatibility of the molar conceptus with the mother may be an element of the process that prevent its early rejection.

A series of 226 antenatal diagnoses of chromosome structural re-arrangements in 181 couples has shown the usefulness of such diagnosis for couples including a genitor carrying a balanced anomaly. Analysis of the data has elicited major variations in the incidence of unbalanced anomalies in foetal cells and has provided information which can usefully be applied to genetic counselling.

The authors' experience of 155 prenatal diagnoses of inborn errors of metabolism shows that such diagnoses cannot be made without an extensive network of laboratories specialized in cell biology and biochemistry. The enzymatic deficiency must also be clearly established in each family at risk, and the value of enzymatic assay techniques must be demonstrated on cultures of skin fibroblasts and amniotic fluid cells. In this series, 126 diagnoses of 25 different autosomal recessive metabolic diseases were made; 23 foetuses were affected. Twenty-nine diagnoses concerned 5 types of X-linked metabolic diseases; since non-obligatory carrier women also had a prenatal diagnosis, the diseases were detected in only 5 foetuses.

A pericentric inversion of chromosome 2 has been detected in 4 unrelated families. The break points are identical in band 2p11 and band 2q13. Reproductive history of these couples is analyzed. The pathology of these particular regions of chromosome 2 is discussed.

A prenatal diagnosis of fragile X fra(X)(q28) has been performed in a pregnant woman obligate carrier of fra(X) by analysis of amniotic fluid cells taken by amniocentesis. The fra(X) has been observed in 30% (8/26) of the metaphases of the male fetus. These results were obtained within 10 days after amniocentesis using the in situ technique on cells grown first in Ham Medium supplemented with newborn calf serum and a serum substitute and changed for the last 19 hours with Tc 199 medium with 5% newborn calf serum and methotrexate (10 mg/l). This technique showed that fra(X) is not a clonal phenomenon and that its expression is related to the cell types and the origin of the studied cells.

Carrier diagnosis and prenatal diagnosis of Duchenne's muscular dystrophy (DMD) and Becker's muscular dystrophy (BMD) has become possible using some twenty RFLPs detected by more than a dozen Xp21 probes that are either intragenic or flanking the disease locus. Results from familial studies on 88 DMD and BM families stress important considerations concerning a priori and final risks, individuals necessary for the identification of the phase, and the different strategies that can be applied, regardless of whether the study concerns an on-going pregnancy or a carrier-status determination, and whether the patient is at high or low risk. Finally, multiple sources of difficulties in interpreting the results depend on a) the occurrence of new mutations that must be traced; b) the existence of meiotic recombination; c) the necessity, in some instances, of relying upon the sole identification of the paternal X. These considerations emphasize the characteristics and the important limitations of this type of methodology.

This article, which is the second installment of a study of the psychological aspects of antenatal diagnosis, presents the analysis of interviews with women (and with some of their partners) who were examined because of their age. The characteristics of these "late" pregnancies seem to be the following: 1. The question of a abnormality shifts the emphasis from the child to the pregnancy itself, which is often lived through as something abnormal; 2. knowing the sex of the child before its birth emphasizes the abnormality of the pregnancy and therefore draws attention to the problem of the age of the mother; 3. this last chance of pregnancy emphasizes the question, which is near in time for these women, of the menopause, of getting old and of death; 4. it also emphasizes in a most emphatic way the question of mourning, of loss, of the place of the future child in the history of the woman and in a more general way the question of the desire to have a baby.