A new mutation in the AFP gene responsible for a total absence of alpha feto-protein on second trimester maternal serum screening for Down syndrome.

Alpha feto-protein (AFP) is a major plasma protein produced by the yolk sac and the liver during the fetal period. During the second trimester of pregnancy, APF and betahCG serum concentrations are commonly used for screening Down syndrome. AFP deficiency is rare (estimated to be 1/105,000 newborns) and only one sequence alteration has previously been reported in the AFP gene. We report a new mutation in exon 5 of the AFP gene, leading to a total absence of AFP on 2nd-trimester maternal serum screening for Down syndrome, confirmed on the amniotic fluid. Despite this, fetal development and birth were normal. After PCR-amplification, the whole AFP gene was sequenced. The new mutation was a guanine to adenine transition in position 543 creating a premature stop codon in position 181. In order to search for eventual modifications of the amniotic fluid profile, proteins were separated by electrophoresis and compared with 10 normal amniotic fluids sampled at the same developmental age (18 weeks). In the amniotic fluid of our patient albumin rate was reduced whereas alpha1 and beta protein fractions were increased, suggesting that AFP deficiency may modify the distribution of protein fractions. This observation emphasizes the complex molecular mechanisms of compensation of serum protein deficiency. Studies on other families with AFP deficiency are necessary to confirm this observation.

The Tunisian population history through the Crigler-Najjar type I syndrome.

Crigler-Najjar syndrome type I (CN-I) is a rare and severe metabolic disorder. A recurrent mutation - c.1070A>G in exon 3 - was identified in the Tunisian population, suggesting a founder effect. In 2004, the detection of this mutation in two Kuwaiti Bedouin families has called the Tunisian founder effect in question again. To determine the origin of this mutation, 21 Tunisian and 2 Kuwaiti Bedouin CN-I patients were screened using nine genetic markers. Haplotype analysis confirmed the founder effect hypothesis and dated the appearance of this mutation some 32 generations ago in the Tunisian population. Using the same genetic analysis, the ancestor haplotype was identified in these two families. This result genetically confirms the blending of the Bedouin nomads within today's Tunisian population. After population migration from east to west, this mutation was introduced into the Tunisian population, and then perpetuated, probably because of marriages in isolated communities.

Paternal isodisomy for chromosome 2 as the cause of Crigler-Najjar type I syndrome.

Crigler-Najjar syndrome type I (CN-I) is a rare and severe autosomal recessive metabolic disease due to a total deficiency of bilirubin uridine diphosphate glucuronosyltransferase located on chromosome 2. We report on a child with CN-I due to a phenylalanine residue deletion inherited only from the father carrying this deletion at the heterozygous state. Cytogenetic analyses showed no deletion of the chromosomal 2q37 region. Microsatellite analysis of the child and his parents was consistent with paternal isodisomy for chromosome 2 in the child. This report demonstrates that uniparental disomy may be at the origin of very rare diseases transmitted as autosomal recessive traits and emphasizes the need for parental DNA analysis in such cases.

Prenatal diagnosis of Crigler-Najjar syndrome type I by single-strand conformation polymorphism (SSCP).

Crigler-Najjar syndrome type I (CN-I) is a rare and severe inherited disorder of bilirubin metabolism, caused by the total deficiency of bilirubin-UDP-glucuronosyltransferase (UGT) activity. Enzymatic diagnosis cannot be performed in chorionic villi or amniocytes as UGT is not active in these tissues. The cloning of the UGT1 gene and the identification of disease-causing mutations have led to the possibility of performing DNA-based diagnosis. Here we report DNA-based prenatal diagnosis of CN-I in two Tunisian families in whom CN-I patients were diagnosed. As we had previously shown that CN-I was, in Tunisia, associated with homozygosity for the Q357R mutation within the UGT1 gene, we were able to detect this mutation in both families and to show that it was easily recognized by single-strand conformation polymorphism (SSCP) analysis. In both cases, SSCP analysis of fetal DNA showed that the fetus was heterozygous for the Q357R mutation. In one family, the pregnancy was carried to term and a healthy baby was born, whereas, in the other family, the pregnancy is still continuing. Thus the prenatal diagnosis of CN-I is possible, provided disease-causing mutations have been identified. SSCP analysis of DNA prepared either from amniocytes or from chorionic villi is a simple, reliable and fast method for prenatal diagnosis.

Is a polymorphism of the apolipoprotein E gene associated with preeclampsia?

OBJECTIVE: Apolipoprotein E (apo E) is pivotal in lipid metabolism. In women with preeclampsia, an atherogenic state is observed. We hypothesized that a particular genotype of apo E may be associated with preeclampsia. METHODS: Genomic DNA was extracted from 55 normotensive and 49 preeclamptic women (defined according to the American College of Obstetricians and Gynecologists criteria). DNA was amplified by PCR and digested simultaneously by AflIII and HaeII giving profiles identifying all the possible genotypes of apo E. RESULTS: The most common isoform apo E3 was found both for normotensive and preeclamptic women (76% and 85%, respectively). The frequency of apo E2 and E4, which are more atherogenic, was not higher in the preeclamptic population. CONCLUSION: We were unable to demonstrate that the "atherogenic state" of preeclampsia is associated with a particular genotype of apo E. Familial studies show that shared genetic and environmental factors are involved in lipid variability. However, owing to the diversity of factors contributing to the development of preeclampsia (fetal and paternal genotypes), these data do not allow to rule-out a possible contribution of maternal apo E to preeclampsia.