Decline in prevalence of neural tube defects in a high-risk region of the United States.

OBJECTIVES: To conduct surveillance for neural tube defects (NTDs) in a high-risk region of the United States and to prevent occurrence and recurrence of NTDs through the periconceptional use of folic acid supplements. DESIGN: Active and passive methods were used for surveillance of NTD-affected pregnancies and births during a 6-year period (October 1992-September 1998). Individual genetic counseling was used to prevent NTD recurrences and a public awareness campaign was used to reduce NTD occurrences. SETTING: State of South Carolina. PATIENTS: All cases of spina bifida, anencephaly, and encephalocele identified among 278 122 live births and fetal deaths to South Carolina residents during 1992-1998 were included. MAIN OUTCOME MEASURE: Changes in occurrence and recurrence rates during a 6-year period. RESULTS: Over the 6 years of surveillance, the prevalence rates for NTDs decreased from 1.89 to.95 cases per 1000 live births and fetal deaths. The prevalence decrease is explained primarily by a decrease in cases of spina bifida. Isolated NTDs accounted for 297/360 (82%) NTDs and 63/360 (18%) had at least 1 other structural anomaly. Females predominated among isolated NTDs but the sex distribution was equal among NTD cases with other anomalies. Prevalence rates for whites (1.48 cases per 1000 live births and fetal deaths) were higher than rates for blacks (.87 cases per 1000 live births and fetal deaths). There were no NTD recurrences in 113 subsequent pregnancies to mothers of infants with isolated NTDs who took periconceptional folic acid. The rate of periconceptional folic acid use among women of childbearing years increased from 8% to 35% during the 6-year project period. CONCLUSION: The prevalence of NTDs in a high-risk region has declined coincident with the increased periconceptional use of folic acid supplements among women of childbearing age.neural tube defects, high-risk region, birth defects, folic acid, spina bifida, anencephaly, encephalocele.

The activin receptor-like kinase 1 gene: genomic structure and mutations in hereditary hemorrhagic telangiectasia type 2.

The activin receptor-like kinase 1 gene (ALK-1) is the second locus for the autosomal dominant vascular disease hereditary hemorrhagic telangiectasia (HHT). In this paper we present the genomic structure of the ALK-1 gene, a type I serine-threonine kinase receptor expressed predominantly in endothelial cells. The coding region is contained within nine exons, spanning < 15 kb of genomic DNA. All introns follow the GT-AG rule, except for intron 6, which has a TAG/gcaag 5' splice junction. The positions of introns in the intracellular domain are almost identical to those of the mouse serine-threonine kinase receptor TSK-7L. By sequencing ALK-1 from genomic DNA, mutations were found in six of six families with HHT either shown to link to chromosome 12q13 or in which linkage of HHT to chromosome 9q33 had been excluded. Mutations were also found in three of six patients from families in which available linkage data were insufficient to allow certainty with regard to the locus involved. The high rate of detection of mutations by genomic sequencing of ALK-1 suggests that this will be a useful diagnostic test for HHT2, particularly where preliminary linkage to chromosome 12q13 can be established. In two cases in which premature termination codons were found in genomic DNA, the mutant mRNA was either not present or present at barely detectable levels. These data suggest that mutations in ALK-1 are functionally null alleles.

Folic acid in the prevention of birth defects.

Maternal use of folic acid prior to conception reduces the risk for neural tube defects. In addition, other birth defects may be prevented by the periconceptional use of folic acid. Homocysteine-methionine metabolism appears to be altered in women with pregnancies affected by neural tube defects; however, the specific mechanisms of causation are not yet known. Fortification of flour with folic acid has been approved by the Food and Drug Administration, although at a level that still requires folic acid supplementation as recommended by the Public Health Service for all women of childbearing age to prevent neural tube defects.

5,10 Methylenetetrahydrofolate reductase genetic polymorphism as a risk factor for neural tube defects.

Persons with a thermolabile form of the enzyme 5,10 methylenetetrahydrofolate reductase (MTHFR) have reduced enzyme activity and increased plasma homocysteine which can be lowered by supplemental folic acid. Thermolability of the enzyme has recently been shown to be caused by a common mutation (677C-->T) in the MTHFR gene. We studied 41 fibroblast cultures from NTD-affected fetuses and compared their genotypes with those of 109 blood specimens from individuals in the general population. 677C-->T homozygosity was associated with a 7.2 fold increased risk for NTDs (95% confidence interval: 1.8-30.3; p value: 0.001). These preliminary data suggest that the 677C-->T polymorphism of the MTHFR gene is a risk factor for spina bifida and anencephaly that may provide a partial biologic explanation for why folic acid prevents these types of NTD.

The impact of prenatal diagnosis on NTD surveillance.

Active and passive surveillance methods were utilized in an attempt to identify all neural tube defect (NTD)-affected pregnancies in South Carolina, a state previously identified to have a high prevalence of these defects (Greenberg et al., 1983). Sources of case ascertainment included maternal serum alpha-fetoprotein (MSAFP) programmes, prenatal diagnosis (amniocentesis) programmes, physician offices, perinatal centres, hospital medical record departments, and vital records. One hundred and nine NTD cases were identified over 24 months, indicating a prevalence of 1.60 cases per 1000 recorded births and fetal deaths (surveillance 1 October 1992-30 September 1994). Fifty-three (49 per cent) of the 109 NTD-affected pregnancies were either spontaneously or electively aborted prior to 26 weeks' gestation. Only three (6 per cent) of these early termination NTD cases were recorded in vital records, while medical records recorded 40 cases (75 per cent). By monitoring MSAFP programmes and maintaining frequent contact with physician offices and perinatal centres, 85 per cent of these early termination NTD-affected pregnancies were identified. However, for complete ascertainment of NTD-affected pregnancies, the utilization of all of these ascertainment methods was necessary, as each ascertainment method identified NTD cases missed by the other methods. Consideration of the significant impact of prenatal diagnosis on NTD surveillance and the use of multiple ascertainment methods in an attempt at complete ascertainment is particularly important now because of the recent recommendation for the periconceptional use of folic acid to prevent neural tube defects and the need for epidemiological studies to monitor the effectiveness of this prevention.

Molecular characterization of breakpoints in patients with holoprosencephaly and definition of the HPE2 critical region 2p21.

Holoprosencephaly (HPE) is a common developmental defect involving the brain and face in humans. Cytogenetic deletions in patients with HPE have localized one of the HPE genes (HPE2) to the chromosomal region 2p21. Here we report the molecular genetic characterization of nine HPE patients with cytogenetic deletions or translocations involving 2p21. We have determined the parental origin of the deleted chromosomes and defined the HPE2 critical region between D2S119 and D2S88/D2S391. As a first step towards cloning the HPE2 gene which is crucial for normal brain development we have constructed a YAC contig which spans the smallest region of deletion overlap. Several of these YACs could be identified which span three different 2p21 breakpoints in HPE patients. These YACs narrow the HPE2 critical region to less than 1 Mb and are now being further analyzed to identify the gene causing holoprosencephaly on chromosome 2.

Metallothionein protects against the cytotoxic and DNA-damaging effects of nitric oxide.

In inflammatory states, nitric oxide (.NO) may be synthesized from precursor L-arginine via inducible .NO synthase (iNOS) in large amounts for prolonged periods of time. When .NO acts as an effector molecule under these conditions, it may be toxic to cells by inhibition of iron-containing enzymes or initiation of DNA single-strand breaks. In contrast to molecular targets of .NO, considerably less is known regarding mechanisms by which cells become resistant to .NO. Metallothionein (MT), the major protein thiol induced in cells exposed to cytokines and bacterial products, is capable of forming iron-dinitrosyl thiolates in vitro. Therefore, we tested the hypothesis that overexpression of MT reduces the sensitivity of NIH 3T3 cells to the .NO donor, S-nitrosoacetylpenicillamine (SNAP), and to .NO released from cells (NIH 3T3-DFG-iNOS) after infection with a retroviral vector expressing human iNOS gene. There was a 4-fold increase in MT in cells transfected with the mouse MT-1 gene (NIH 3T3/MT) compared to cells transfected with the promoter-free inverted gene (NIH 3T3/TM). NIH 3T3/MT cells were more resistant than NIH 3T3/TM cells to the cytotoxic effects of SNAP (0.1-1.0 mM) or .NO released from NIH 3T3-DFG-iNOS cells. A brief (1 h) exposure to 10 mM SNAP caused DNA single-strand breaks that were 9-fold greater in NIH 3T3/TM compared to NIH 3T3/MT cells. Electron paramagnetic resonance spectroscopy of NIH 3T3 cells revealed a greater peak at g = 2.04 (e.g., iron-dinitrosyl complex) in NIH 3T3/MT than NIH 3T3/TM cells. These data are consistent with a role for cytoplasmic MT in interacting with .NO and reducing .NO-induced cyto- and nuclear toxicity.

Social and reproductive behaviors in surrogate-reared squirrel monkeys (Saimiri sciureus).

A colony of 16 surrogate-reared squirrel monkeys was observed for the adequacy of social and reproductive behaviors at maturity. Aside from some self-directed abnormalities centering around nonnutritive orality, this group was behaviorally normal in spite of having no contacts with mother-reared, older conspecifics. Half (N=5) of the females gave birth, with four infants viable. One infant has remained with the colony and is thriving. The other three remained with the group for as long as 42 days before death or removal. Maternal care appeared adequate. Mean estimated conception age for females was 35 months, and the mean impregnation age for males was estimated to be 42 months.

Experimental infection of chimpanzees with the Norwalk agent of epidemic viral gastroenteritis.

A fecal filtrate of human origin containing the Norwalk agent of epidemic viral gastroenteritis was administered by stomach tube to chimpanzees in an attempt to induce diarrheal disease. Significant postchallenge serum antibody rises against Norwalk viral antigens were demonstrated in all animals using the techniques of immune electron microscopy and radioimmunoassay. In addition, viral antigens were detected in feces from five of nine animals using radioimmunoassay. Clinical illness characterized by diarrhea and/or vomiting did not occur. Infection was transmitted subsequently by feeding four additional chimpanzees a fecal filtrate prepared from one of the previously infected animals. Development of an antibody response in four animals and detection of viral antigen in two animals that received this passage filtrate indicated that viral replication had occurred in the absence of clinical illness. The availability of the chimpanzee as an experimental animal host susceptible to infection with the Norwalk agent should facilitate the study of epidemic viral gastroenteritis.

Herpesvirus saimiri-induced malignant lymphoma in rabbits.

Of 9 New Zealand White rabbits inoculated at multiple sc and im sites with a single dose of Herpesvirus saimiri (HVS), 2 developed malignant lymphomas 40-50 days post inoculation. At least 1 animal developed a terminal leukemic phase of the disease. HVS was isolated from the oral and conjunctival swabs and blood and tissue lymphocytes, but not from monolayer cell cultures derived from kidney or lung tissues of the diseased animals. The inoculated rabbits developed low titers of neutralizing antibodies against the virus. Antibodies against HVS specific early and late antigens were not detected in the sera of 7 animals that failed to develop clinical disease, but were detected in the serum of the 1 rabbit with lymphoma. The immunologic response of rabbits to HVS infection was compared to similar responses in infected nonhuman primates.

Response to primary infection with Herpesvirus saimiri in immunosuppressed juvenile and newborn squirrel monkeys.

Immunosuppression of juvenile squirrel monkeys with combined azathioprine, prednisolone, and antilymphocyte globulin resulted in decreased antibody responses to viral antigens after primary infection with Herpesvirus saimiri (HVS). The virus was repeatedly isolated from the oropharynx of immunosuppressed monkeys but not from untreated infected controls. Thus immune factors are important in inhibiting shedding of HVS from the oropharynx. HVS could be isolated from the peripheral blood lymphocytes of infected control monkeys but not from the lymphocytes of immunosuppressed monkeys. Immunosuppressed monkeys also had decreased percentages of lymphocytes capable of forming rosettes with sheep erythrocytes. These results indicate that the immunosuppressive agents had inhibitory effects on lymphocytes (presumably thymus derived) capable of being latently infected with HVS. Antibody responses in newborn monkeys infected with HVS were delayed compared with juvenile monkeys. Treatment of newborn monkeys with antilymphocyte globulin had no suppressive effect on antibody responses to HVS.