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Prenatal diagnosis in adenylosuccinate lyase deficiency.

Adenylosuccinate lyase deficiency, an autosomal recessive inborn error of purine synthesis, provokes accumulation in body fluids of succinylaminoimidazolecarboxamide riboside and succinyladenosine, the dephosphorylated derivatives of the two substrates of the enzyme. Most patients display severe psychomotor retardation, often accompanied by epilepsy and/or autistic features, although some are only mildly retarded. About 20 mutations are known. Prenatal diagnosis was performed twice on chorion villi of the mother of a previously diagnosed patient with a C5T mutation (exon 1) on the maternal allele, and a C1185A mutation (exon 11) on the paternal allele. Both suppress a Fnu4HI restriction site. In a first fetus, incubation of PCR products generated from genomic DNA of exon 1 with Fnu4HI yielded a 113 bp fragment from a control and the father's gene, and both a 113 bp and 170 bp fragment from the mother, affected sibling and fetus. Incubation of PCR products of exons 11-12 with Fnu4HI yielded a 550 bp fragment from a control and the mother's gene, and a 550 bp and 600 bp fragment from the father, affected sibling and fetus. Assay of adenylosuccinate lyase on the aborted fetal liver confirmed the enzyme deficiency. A second fetus displayed only the maternal mutation.

Abortion, Induced↗

Prenatal diagnosis of mosaicism for a del(22)(q13).

A case of prenatally detected mosaicism for a del(22)(q13) is reported. CVS was performed because of abnormal fetal ultrasound findings: cystic 'tumour' in the fetal neck and the upper thoracic aperture. Karyotypes from chorionic villi were suspicious of an aberration concerning the long arm of one chromosome 22. FISH analysis demonstrated mosaicism for a distal 22q deletion in fetal fibroblasts. The deletion was postnatally confirmed by FISH with a chromosome-specific 22q probe. The 'tumour' on autopsy turned out to be cystic thymic tissue. Apart from this, no other obvious fetal anomalies were found.

Adult↗

Apparent confined placental mosaicism of trisomy 16 and multiple fetal anomalies: case report.

Trisomy 16 is frequently found confined to the placenta (confined placental mosaicism (CPM)), with a structurally normal fetus. In some cases of trisomy 16, the fetus has uniparental disomy for chromosome 16 (UPD16) which is associated with intrauterine growth restriction (IUGR) and fetal anomalies. We report a case of apparent confined placental mosaicism for trisomy 16, using standard cytogenetic techniques, but with multiple fetal abnormalities including congenital diaphragmatic hernia in which there was no evidence of UPD in the disomic tissues examined. Subsequent examination of fetal tissues using fluorescent in situ hybridization (FISH) demonstrated low levels of mosaicism for trisomy 16 in all the tissues examined. The use of FISH permits identification of mosaicism which conventional techniques may not identify.

Abnormalities, Multiple↗

Maternal uniparental disomy of chromosome 16 and body stalk anomaly.

We report on a fetus with placental trisomy 16, maternal uniparental disomy (UPD), and body stalk anomaly. Body stalk anomaly is a rare, fatal developmental abnormality consisting of a defective abdominal wall with abdominal organs in a sac outside the abdominal cavity covered by amnion adherent to the placenta with absence or severe shortness of the umbilical cord. Trisomy 16 was identified in the placenta in all cells. Amniocentesis was karyotypically normal. Parental origin studies showed maternal UPD for chromosome 16 in post-termination fetal tissue. The cause of the body stalk anomaly is not clearly defined. There are no other reports of placental karyotype or UPD investigations with body stalk anomaly. To our knowledge, this is the first report of placental trisomy 16, UPD in fetus, and body stalk anomaly, suggesting placental insufficiency or imprinting effects as cause of this anomaly. Am. J. Med. Genet. 94:284-286, 2000.

Abdominal Muscles↗

The Genoa experience of prenatal diagnosis in NF1.

Type 1 neurofibromatosis (NF1) is an autosomal dominant disorder with an incidence of about 1 in 3500 live births. Symptoms are highly variable from a few cafè-au-lait spots and axillary freckling to plexiform neurofibromas, optic gliomas, pseudarthrosis, and malignancy. Since disease causing mutations are dispersed throughout the gene, prenatal diagnosis is usually performed in familial cases by linkage analysis and rarely by direct characterization of the mutation. We have characterized 48 families and have performed four prenatal diagnoses. In three cases, the linkage analysis was carried out using informative markers. A direct approach using the protein truncation test (PTT) and sequencing was performed in one case in which a R1947X mutation was identified. The extreme variability of the phenotypic expression of the NF1 gene makes reproductive decisions in NF1 families very difficult, as molecular diagnosis cannot predict clinical expression of the disease. The psychological management of the couple is therefore difficult. In two of the three examined families the reproductive choices were not influenced by the specific manifestations of the disease in that family.

Adult↗

Determination of enzyme activities for prenatal diagnosis of respiratory chain deficiency.

Genetic counselling and prenatal diagnosis are major issues of mitochondrial respiratory chain deficiency, especially as these conditions are largely untreatable. In the absence of known mitochondrial or nuclear gene mutations, measurement of respiratory chain enzyme activities represents the only possibility to prevent recurrence of the disease in affected families. We carried out enzymatic prenatal diagnosis in 21 pregnancies from 10 unrelated couples using uncultured choriocytes and/or amniocytes. Twelve babies were born and are healthy, seven pregnancies were discontinued early on because of an enzyme deficiency detected prenatally. In two cases, a fetus which appeared normal after early and/or late prenatal diagnosis, turned out to be affected. We conclude that a deficient enzyme activity is indicative of recurrence, but a normal result at 10 weeks of gestation does not give conclusive evidence as to the outcome of the pregnancy. We therefore suggest the following procedure: (1) a choriocentesis or an amniocentesis in early pregnancy when the proband expresses the disease in cultured skin fibroblasts; (2) a second amniocentesis at 28 weeks' gestation should be offered to avoid false negative results due to a possible late expression of the disease, in combination with: (3) a careful and repeated ultrasound survey for detection of growth failure in the third trimester; (4) prenatal diagnosis should not be performed in case of late onset clinical symptoms in the proband; and (5) parents should be aware of the possibility of false negative results. Prenatal diagnosis should not be proposed for a complex I deficiency as this enzyme activity cannot be accurately measured in fetal cells.

Adult↗

Prenatal diagnosis of glycogen storage disease type 1b using denaturing high performance liquid chromatography.

Glycogen storage disease type 1b (GSD1b) is an autosomal recessive inborn error of metabolism caused by deficiency of glucose-6-phosphate translocase (G6PT1). Current laboratory diagnosis for GSD1b is established by a functional enzyme assay of glucose-6-phosphatase in both fresh and detergent-treated liver homogenates. This procedure requires liver biopsy and is impractical for routine prenatal diagnosis owing to the high morbidity of fetal liver biopsy. Recently, the gene for GSD1b has been cloned and the prevalent mutations in different ethnic groups have been determined. In this study, prenatal molecular diagnosis was performed for a Chinese family in which a previous child was born homozygous for the G149E mutation. We detected genomic sequence variants by heteroduplex formation, followed by denaturing high performance liquid chromatography (DHPLC). With this method, post-PCR analysis was shortened to 7 min. In the case we analysed, PCR products amplified from the fetal DNA yielded a single peak in the chromatogram, indicating a homozygous state in the fetus. When wild-type PCR products were mixed with fetal PCR products, two peaks were observed, indicating that the fetus was homozygous for the parental (G149E) mutation. Sequencing results confirmed this diagnosis. As a result, the pregnancy was terminated and the diagnosis was confirmed on DNA analysis of the aborted fetus. We show here that DNA mutation analysis can be used in the prenatal diagnosis of GSD1b and that DHPLC promises to be a robust technique for this and other prenatal molecular diagnoses.

Abortion, Eugenic↗

First-trimester diagnosis of late-infantile neuronal ceroid lipofuscinosis (LINCL) by tripeptidyl peptidase I assay and CLN2 mutation analysis.

Late-infantile neuronal ceroid lipofuscinosis (LINCL) is a progressive neurodegenerative disorder caused by the deficiency of lysosomal tripeptidyl peptidase I (TPP-I) encoded by the CLN2 gene. We report the first case of early prenatal diagnosis of LINCL by combined enzyme and mutation analysis. TPP-I activity in chorionic villi (CV) was less than 2% of the mean normal control level and g.1946A > G and g.3670C > T mutations were demonstrated, as in the two previously affected children. After termination of pregnancy, TPP-I deficiency was confirmed in cultured CV cells and in the fetal skin fibroblasts. The expression of unequivocal TPP-I deficiency in CV demonstrates that enzyme assay is a reliable option for prenatal diagnosis of LINCL.

Aminopeptidases↗

Fetal akinesia deformation sequence: a study of 30 consecutive in utero diagnoses.

The etiology of the fetal akinesia deformation sequence (FADS) is heterogeneous and can be the result of neurogenic and myopathic disorders, restrictive dermopathy, teratogen exposure, and intrauterine constraint. We present the prenatal and fetopathological findings in a consecutive series of 30 affected fetuses with normal chromosomal results. According to the in utero time of onset of the fetal akinesia, the severity of the phenotype varied from a severe, generalized FADS in the early-onset group to milder defects, as isolated distal arthrogryposis in the late-onset group. No more than 10% (3/30) were diagnosed in the first trimester of pregnancy and all presented a severe phenotype. Twenty-seven of the thirty (90%) were diagnosed after the first trimester, with a severe FADS in 15/27 and a milder phenotype of distal arthrogryposis in 12/27. In all 30 patients, extensive neuropathological studies (brain, spinal cord, and muscles) were performed. In 16 patients (53%) a specific diagnosis could be made (central nervous system abnormalities 9/16; spinal cord 1/16; primary myopathy 3/16; syndromic 3/16). In 10 others (33%), pathological neuromuscular findings were present but no definitive diagnosis was established. In 4 patients (13%), neuromuscular findings were normal, and the etiology of the FADS remained unexplained.

Abnormalities, Multiple↗

Prenatal diagnosis of the fragile X--the Australasian experience.

Identification of increasing numbers of females heterozygous for fragile X linked mental retardation together with improved genetic counselling is creating a growing demand for prenatal diagnosis of fra(X). However, present cytogenetic techniques are somewhat unreliable and our collaborative approach has endeavoured to improve quality of cell culture systems and the sensitivity of fra(X) detection. Since 1985 we have exchanged cell cultures between our laboratories for verification of diagnostic results and comparison of induction techniques and have benefitted from larger numbers of cells scored for fra(X). Our 50 cases represent almost all of such studies undertaken in Australasia (Australia and New Zealand). Ten cases were unequivocally fra(X) positive; there was discrepancy between laboratories in 4 cases and one false-negative case. We propose a protocol to enhance fra(X) detection and conclude that, provided care is exercised, couples at risk of a fra(X) pregnancy can benefit from prenatal cytogenetic diagnosis.

Amniocentesis↗

Interpretation of chromosome mosaicism and discrepancies in chorionic villi studies.

In 3,000 chorionic villi studies (CVS) 33 cases of mosaicism and 7 false-positive cell lines in all cells were seen. The mosaic cell lines were caused by aneuploidy of autosomes (13x), sex chromosomes (9x), and structural anomalies (11x). Mosaics of fetal origin were only 4 cases of trisomy 21 and one 47,XXY mosaic. In 7 cases abnormal karyotype of non-fetal origin was seen in all cells in direct studies, including trisomy 16 (3x) and trisomy 18 (2x). The combined use of direct CVS and cell cultures always uncovered the non-fetal origin of chromosome abnormalities and the study of cultured cells in all cases could have prevented 5 terminations. Complete follow-up studies demonstrated no false-negative results. Therefore, CVS can be nearly 100% accurate when both direct studies and cultures are examined in cases of mosaicism and other cell lines of possible non-fetal origin, such as trisomy 16, trisomy 18, translocation (21;21), and 45,X cells.

Aneuploidy↗

Analysis of full fragile X mutations in fetal tissues and monozygotic twins indicate that abnormal methylation and somatic heterogeneity are established early in development.

The fragile X syndrome, the most common cause of inherited mental retardation, is characterized by unique genetic mechanisms, which include amplification of a CGG repeat and abnormal DNA methylation. We have proposed that 2 main types of mutations exist. Premutations do not cause mental retardation, and are characterized by an elongation of 70 to 500 bp, with little or no somatic heterogeneity and without abnormal methylation. Full mutations are associated with high risk of mental retardation, and consist of an amplification of 600 bp or more, with often extensive somatic heterogeneity, and with abnormal DNA methylation. To analyze whether the latter pattern is already established during fetal life, we have studied chorionic villi from 10 fetuses with a full mutation. In some cases we have compared them to corresponding fetal tissues. Our results indicate that somatic heterogeneity of the full mutation is established during (and possibly limited to) the very early stages of embryogenesis. This is supported by the extraordinary concordance in mutation patterns found in 2 sets of monozygotic twins (9 and 30 years old). While the methylation pattern specific of the inactive X chromosome appears rarely present on chorionic villi of normal females, the abnormal methylation characteristic of the full mutation was present in 8 of 9 male or female chorionic villi analyzed. This suggests that the methylation mechanisms responsible for establishing the inactive X chromosome pattern and the full mutation pattern are, at least in part, distinct. Our results validate the analysis of chorionic villi for direct prenatal diagnosis of the fragile X syndrome.

Adult↗