Prenatal diagnosis and molecular characterization of an interstitial 1q24.2q25.2 deletion.

We report on the observation of an interstitial deletion of the long arm of chromosome 1 diagnosed prenatally in a 28 weeks gestation fetus by standard karyotype. Amniocentesis was performed because of an increased Down syndrome maternal serum screening and ultrasonographic abnormalities. Fetus autopsy showed an intrauterine growth retardation, dysmorphic features and limbs abnormalities. Using fluorescent in situ hybridization technique (FISH), we characterized the deletion boundaries corresponding to the bacterial artificial chromosomes (BAC) RP11-193J5 and RP11-162L13. Molecular studies identified the deletion of paternal origin. Therefore the karyotype was interpreted as 46,XY,del(1)(q24.2q25.2). This is the smallest deletion of the long arm of chromosome 1 reported prenatally and characterized at the molecular level. Its phenotype is compared to other similar cases described in the literature.

Identification of novel L1CAM mutations using fluorescence-assisted mismatch analysis.

The L1CAM gene, which is located in Xq28 and codes for a neuronal cell adhesion molecule, is involved in three distinct conditions: HSAS (hydrocephalus-stenosis of the aqueduct of Sylvius), MASA (mental retardation, aphasia, shuffling gait, adductus thumbs), and SPG1 (spastic paraplegia). Molecular analysis of the L1CAM gene is labor-intensive because of the size of the coding region, which is fragmented in numerous exons, and because of the great allelic heterogeneity and distribution of the mutations. The FAMA (fluorescent assisted mismatch analysis) method combines the excellent sensitivity of the chemical cleavage method for scanning PCR fragments larger than 1 kb and the power of automated DNA sequencers. In order to optimize this method for L1CAM, we divided the gene into nine genomic fragments, each including three to four exons. These fragments were PCR-amplified using nine sets of primers containing additional rare universal sequences. A second-stage PCR, per formed with the two dye-labeled universal primers, allowed us to generate 1-kb-labeled fragments, which were then submitted to the chemical cleavage analysis. Among 12 French families with HSAS and/or MASA, we identified nine distinct L1CAM mutations, seven of which were novel, and an intronic variation. This study demonstrates that FAMA allows rapid and reliable detection of mutations in the L1CAM gene and thus represents one of the most appropriate methods to provide diagnosis for accurate genetic counseling in families with HSAS, MASA, or SPG1.

Prezygotic origin of the isochromosome 12p in Pallister-Killian syndrome.

Pallister-Killian syndrome is a rare disorder comprising multiple congenital anomalies, streaks of hypo(hyper)pigmentation, seizures, profound mental retardation, and the presence of an extra metacentric chromosome i(12)(p10), usually limited to skin fibroblasts. The mechanism and parental origin of the extra chromosome i(12)(p10) are unknown. Here, we present a girl with Pallister-Killian syndrome and the i(12)(p10) in 50% of cultured skin fibroblasts. Using microsatellite DNA markers of chromosome 12p, we detected 3 alleles--including 2 different alleles of maternal origin--in cultured skin fibroblasts, suggesting that the tetrasomy 12p is the result of a prezygotic event, with a nondisjunction event during maternal meiosis.

Prenatal diagnosis in France.

Prenatal diagnosis (PND) is very developed in France, especially in the area of ultrasound (US) screening. The activity is regulated by law, and laboratories have to be authorized to perform any type of prenatal biological test if the purpose is to diagnose fetal defects. There are 70 cytogenetics laboratories and 50 biochemistry laboratories performing serum marker screening, about half of them being private. PND of chromosomal anomalies is offered to women over 37 years of age, to women who already had a child with a chromosomal anomaly, in case of abnormal US findings, if one of the parents has a balanced chromosomal anomaly and if the risk of chromosomal anomaly is higher than 1:250 according to the serum markers. Half of the trisomy 21 cases are now detected prenatally and pregnancies terminated. Fetal cell sampling is performed by amniocentesis in 70% of cases, by chorionic villus sampling in 7% of cases and by fetal blood sampling in 23% of cases. There are no professional guidelines and no quality assessment networks for any of the techniques in use. PND is regulated by two major laws: the Law on Abortion (1975) and the Law on Bioethics (1994).

Amniotic fluid digestive enzymes: diagnostic value in fetal gastrointestinal obstructions.

The diagnostic value of amniotic fluid gamma-glutamyl-transpeptidase (GGTP) and intestinal alkaline phosphatase (iALP) was evaluated in 55 patients who underwent amniocentesis for karyotyping because fetal gastric or small bowel dilatation had been detected by ultrasound. Gastrointestinal malformation was confirmed in 46 cases and there was no gastrointestinal anomaly in nine cases. Prenatal ultrasound was suggestive of gastroduodenal dilatation in 34 cases (group I) and small bowel dilatation in 21 cases (group II). In group I, amniotic fluid GGTP above the 99th percentile was 71 per cent sensitive and 100 per cent specific for a true anatomical defect of the digestive tract (mainly duodenal atresia). In group II, high levels of GGTP and/or iALP were 69 per cent sensitive and 83 per cent specific for a fetal digestive tract anomaly. In other words, when digestive tract dilatations were diagnosed by prenatal sonography, abnormal amniotic fluid enzyme activities were strongly suggestive of such an anomaly, the possibility of which was not precluded by normal amniotic fluid iALP and GGTP activities. But amniotic fluid digestive enzyme activities do not help in defining the prognosis.

Anti-müllerian hormone in early human development.

Anti-müllerian hormone (AMH) is a glycoprotein produced by immature Sertoli cells and responsible for the regression of müllerian ducts in male fetuses. The ontogeny of the hormone in early human development was investigated. While no detectable AMH could be found in female fetal serum, in males, the mean +/- S.E.M. AMH serum concentration was 40.5 +/- 3.9 ng/ml from 19 to 30 weeks (n = 13), and 28.4 +/- 6.1 ng/ml from 30 weeks to term (n = 9). The latter value is significantly different from the mean AMH concentration in serum from boys aged 2 months to 2 years (43.1 +/- 3.7), suggesting that AMH production is sluggish during the perinatal period. The serum AMH concentration of a 46,XX male fetus was in the normal range for males. Using in situ hybridization, AMH transcripts were detected in the testicular tissue of all fetuses from 8 weeks onwards, but not in fetal ovaries nor in the yet undifferentiated gonadal tissue of a 7-week-old fetus bearing male-determining DNA sequences. Together, these data indicate that AMH is a reliable marker for the presence of functional testicular tissue and, as such, may be helpful for the diagnosis of fetal sex, particularly in the presence of sex chromosome abnormalities.

Chromosomal prenatal diagnosis: study of 936 cases of intrauterine abnormalities after ultrasound assessment.

Nine hundred and thirty-six prenatal chromosomal analyses were performed by four cytogenetic centres after ultrasound diagnosis of fetal abnormalities, amniotic fluid disorders, fetal growth retardation, and fetal or placental abnormalities. During the same period, 6515 fetal karyotypes were analysed because of maternal age. Frequencies of chromosomal aberrations in each case were respectively 4.4, 6.7 and 15.8 per cent, compared with 3.18 per cent when the fetal karyotype was performed because of maternal age. High rates of chromosomal aberrations are observed in cases of cervical hygroma, limb abnormalities, omphaloceles, duodenal stenosis, hydrocephalus, and facial abnormalities. In the case of polymalformations, this rate was 29.2 per cent. When malformations were seen together with an amniotic fluid disorder or growth retardation, 21.5 per cent chromosomal aberrations were observed. This frequency was 10.4 per cent when growth retardation was associated with an amniotic fluid disorder. Trisomy 13, 18, 21 and monosomy X accounted for 4/5 of all abnormalities in which we observed a high rate of triploidies (4.9 per cent) and balanced (3.3 per cent) or unbalanced (9.8 per cent) non-Robertsonian structural abnormalities. Sonographic ascertainment of these aberrations and prenatal characteristics of major anomalies are discussed.