HLX is a candidate gene for a pattern of anomalies associated with congenital diaphragmatic hernia, short bowel, and asplenia.

Isolated congenital diaphragmatic hernia is often a sporadic event with a low recurrence risk. However, underlying genetic etiologies, such as chromosome anomalies or single gene disorders, are identified in a small number of individuals. We describe two fetuses with a unique pattern of multiple congenital anomalies, including diaphragmatic hernia, short bowel and asplenia, born to first-cousin parents. Whole exome sequencing showed that both were homozygous for a missense variant, c.950A>C, predicting p.Asp317Ala, in the H.20-Like Homeobox 1 (HLX1) gene. HLX is a homeobox transcription factor gene which is relatively conserved across species. Hlx homozygous null mice have a short bowel and reduced muscle cells in the diaphragm, closely resembling the anomalies in the two fetuses and we therefore suggest that the HLX mutation in this family could explain the fetal findings.

Whole-exome analysis of foetal autopsy tissue reveals a frameshift mutation in OBSL1, consistent with a diagnosis of 3-M Syndrome.

BACKGROUND: We report a consanguineous couple that has experienced three consecutive pregnancy losses following the foetal ultrasound finding of short limbs. Post-termination examination revealed no skeletal dysplasia, but some subtle proximal limb shortening in two foetuses, and a spectrum of mildly dysmorphic features. Karyotype was normal in all three foetuses (46, XX) and comparative genomic hybridization microarray analysis detected no pathogenic copy number variants. RESULTS: Whole-exome sequencing and genome-wide homozygosity mapping revealed a previously reported frameshift mutation in the OBSL1 gene (c.1273insA p.T425nfsX40), consistent with a diagnosis of 3-M Syndrome 2 (OMIM #612921), which had not been anticipated from the clinical findings. CONCLUSIONS: Our study provides novel insight into the early clinical manifestations of this form of 3-M syndrome, and demonstrates the utility of whole exome sequencing as a tool for prenatal diagnosis in particular when there is a family history suggestive of a recurrent set of clinical symptoms.

Investigation of NRXN1 deletions: clinical and molecular characterization.

Deletions at 2p16.3 involving exons of NRXN1 are associated with susceptibility for autism and schizophrenia, and similar deletions have been identified in individuals with developmental delay and dysmorphic features. We have identified 34 probands with exonic NRXN1 deletions following referral for clinical microarray-based comparative genomic hybridization. To more firmly establish the full phenotypic spectrum associated with exonic NRXN1 deletions, we report the clinical features of 27 individuals with NRXN1 deletions, who represent 23 of these 34 families. The frequency of exonic NRXN1 deletions among our postnatally diagnosed patients (0.11%) is significantly higher than the frequency among reported controls (0.02%; P = 6.08 × 10(-7) ), supporting a role for these deletions in the development of abnormal phenotypes. Generally, most individuals with NRXN1 exonic deletions have developmental delay (particularly speech), abnormal behaviors, and mild dysmorphic features. In our cohort, autism spectrum disorders were diagnosed in 43% (10/23), and 16% (4/25) had epilepsy. The presence of NRXN1 deletions in normal parents and siblings suggests reduced penetrance and/or variable expressivity, which may be influenced by genetic, environmental, and/or stochastic factors. The pathogenicity of these deletions may also be affected by the location of the deletion within the gene. Counseling should appropriately represent this spectrum of possibilities when discussing recurrence risks or expectations for a child found to have a deletion in NRXN1.

The impact of maternal weight discrepancies on prenatal screening results for Down syndrome.

OBJECTIVE: This study aimed to assess the quantitative impact of maternal weight discrepancy on the screen result for Down syndrome when using Integrated Prenatal Screening and First Trimester Combined Screening. METHODS: The study population consisted of 78,165 women undergoing prenatal screening in Ontario, Canada, and 158 pregnancies affected with Down syndrome at one Ontario center. The study assessed quantitative alterations of the multiple of the median values of first and second-trimester serum markers and the risks of Down syndrome at a set of theoretical weight discrepancies. RESULTS: Weight discrepancies have the greatest impact on screening results when the initial risk is close to the risk cut-off. When the weight discrepancy is 5 lb or greater and the denominator of the initial risk is within 50 of the risk cut-off, the chance that a screen result will change from positive to negative or from negative to positive is 47-55% for women undertaking Integrated Prenatal Screening. This chance is 33-43% for women undertaking First Trimester Combined Screening. CONCLUSION: A weight discrepancy of five or more pounds has a significant impact on the risk of Down syndrome; correction of maternal weight would improve the accuracy of the screening test.

High-resolution array CGH defines critical regions and candidate genes for microcephaly, abnormalities of the corpus callosum, and seizure phenotypes in patients with microdeletions of 1q43q44.

Microdeletions of 1q43q44 result in a recognizable clinical disorder characterized by moderate to severe intellectual disability (ID) with limited or no expressive speech, characteristic facial features, hand and foot anomalies, microcephaly (MIC), abnormalities (agenesis/hypogenesis) of the corpus callosum (ACC), and seizures (SZR). Critical regions have been proposed for some of the more prominent features of this disorder such as MIC and ACC, yet conflicting data have prevented precise determination of the causative genes. In this study, the largest of pure interstitial and terminal deletions of 1q43q44 to date, we characterized 22 individuals by high-resolution oligonucleotide microarray-based comparative genomic hybridization. We propose critical regions and candidate genes for the MIC, ACC, and SZR phenotypes associated with this microdeletion syndrome. Three cases with MIC had small overlapping or intragenic deletions of AKT3, an isoform of the protein kinase B family. The deletion of only AKT3 in two cases implicates haploinsufficiency of this gene in the MIC phenotype. Likewise, based on the smallest region of overlap among the affected individuals, we suggest a critical region for ACC that contains ZNF238, a transcriptional and chromatin regulator highly expressed in the developing and adult brain. Finally, we describe a critical region for the SZR phenotype which contains three genes (FAM36A, C1ORF199, and HNRNPU). Although ~90% of cases in this study and in the literature fit these proposed models, the existence of phenotypic variability suggests other mechanisms such as variable expressivity, incomplete penetrance, position effects, or multigenic factors could account for additional complexity in some cases.

Non-syndromic language delay in a child with disruption in the Protocadherin11X/Y gene pair.

Protocadherin11 is located on both the X and Y chromosomes in Homo sapiens but only on the X chromosome in other hominid species. The pairing of PCDH11Y with PCDH11X arose following a duplicative 3.5 Mb translocation from the ancestral X chromosome to the Y chromosome several million years ago. The genes are highly expressed in fetal brain and spinal cord. The evolutionary consequence of this duplication has been proposed to include the sexual dimorphism of cerebral asymmetry and the hominid specific transition to the capacity for language. We report a case of a male child referred for genetic investigation of severe language delay. Microarray analysis indicated the presence of a 220 Kb intragenic deletion at Xq21.31 involving the PCDH11X gene. Fluorescence in situ hybridization using a BAC probe mapping to intron 2 of the Protocadherin11X/Y gene pair confirmed loss of the locus on both the X and Y chromosomes. The X chromosome deletion was maternally inherited, but the Y chromosome deletion was found to be a de novo occurrence in this child. This finding lends support to the hypothesis that the Protocadherin11X/Y gene plays a role in language development in humans and that rare copy number variation is a possible mechanism for communication disorders.

aCGH detects partial tetrasomy of 12p in blood from Pallister-Killian syndrome cases without invasive skin biopsy.

Pallister-Killian syndrome (PKS) is a genetic disorder characterized by mental retardation, seizures, streaks of hypo- or hyperpigmentation and dysmorphic features. PKS is associated with tissue-limited mosaic partial tetrasomy of 12p, usually caused by an isochromosome 12p. The mosaicism is usually detected in cultured skin fibroblasts or amniotic cells and rarely in phytohemagluttinin-stimulated lymphocytes, which suggests stimulation of T-lymphocytes may distort the percentage of abnormal cells. We recently reported on the identification by microarray-based comparative genomic hybridization (aCGH) of a previously unsuspected case of partial tetrasomy of 12p caused by an isochromosome 12p. Here we report on seven additional individuals with partial tetrasomy of 12p characterized by our laboratory. All individuals were referred for mental retardation/developmental delay and/or dysmorphic features. In each case, aCGH using genomic DNA extracted from whole peripheral blood detected copy-number gain for all clones for the short arm of chromosome 12. In all but one case, FISH on metaphases from cultured lymphocytes did not detect the copy-number gain; in the remaining case, metaphase FISH on cultured lymphocytes showed an isochromosome in 10% of cells. However, interphase FISH using probes to 12p on peripheral blood smears showed additional hybridization signals in 18-70% of cells. Microarray and FISH analysis on cultured skin biopsies from four individuals confirmed the presence of an isochromosome 12p. Our results demonstrate the usefulness of aCGH with genomic DNA from whole peripheral blood to detect chromosome abnormalities that are not present in stimulated blood cultures and would otherwise require invasive skin biopsies for identification.

Genetic education for primary care providers: improving attitudes, knowledge, and confidence.

OBJECTIVE: To increase primary care providers' awareness and use of genetic services; increase their knowledge of genetic issues; increase their confidence in core genetic competencies; change their attitudes toward genetic testing for hereditary diseases; and increase their confidence as primary care genetic resources. DESIGN: Participants completed a workshop and 3 questionnaires: a baseline questionnaire, a survey that provided immediate feedback on the workshop itself, and a follow-up questionnaire 6 months later. SETTING: Ontario. PARTICIPANTS: Primary care providers suggested by deans of nursing, midwifery, family medicine, and obstetric programs, as well as coordinators of nurse practitioner programs, in Ontario and by the Ontario College of Family Physicians. INTERVENTION: A complex educational intervention was developed, including an interactive workshop and PowerPoint educational modules on genetic topics for participants' use (available at www.mtsinai.on.ca/FamMedGen/). MAIN OUTCOME MEASURES: Awareness and use of genetic services, knowledge of genetics, confidence in core clinical genetic skills, attitudes toward genetic testing, and teaching activities related to genetics. RESULTS: The workshop was attended by 29 participants; of those, 21 completed the baseline questionnaire and the 6-month follow-up questionnaire. There was no significant change found in awareness or reported use of genetic services. There was significant improvement in self-assessed knowledge of (P = .001) and confidence in (P = .005) skills related to adult-onset genetic disorders. There were significant increases in confidence in many core genetic competencies, including assessing risk of hereditary disorders (P = .033), deciding who should be offered referral for genetic counseling (P = .003), discussing prenatal testing options (P = .034), discussing benefits, risks, and limitations of genetic testing (P = .033), and describing what to expect at a genetic counseling session (P = .022). There was a significant increase in the number of primary care providers agreeing that genetic testing was beneficial in the management of adult-onset diseases (P = .031) and in their confidence in being primary care genetic resources for adult-onset genetic disorders (P = .006). CONCLUSION: Educational interventions that include interactive peer resource workshops and educational modules can increase knowledge of and confidence in the core competencies needed for the delivery of genetic services in primary care.

Metabolic syndrome features and risk of neural tube defects.

BACKGROUND: Maternal obesity and pre-pregnancy diabetes mellitus, features of the metabolic syndrome (MetSyn), are individual risk factors for neural tube defects (NTD). Whether they, in combination with additional features of MetSyn, alter this risk is not known. We evaluated the risk of NTD in association with maternal features of the MetSyn. METHODS: We used a population-based case-control study design in the province of Ontario, Canada. Cases and controls were derived from women who underwent antenatal maternal screening (MSS) at 15 to 20 weeks' gestation. There were 89 maternal cases with, and 434 controls without, an NTD-affected singleton pregnancy. Maternal features of MetSyn were defined by the presence of pre-pregnancy diabetes mellitus, body weight > or = 90th centile among controls, non-white ethnicity and/or serum highly sensitive C-reactive protein (hsCRP) > or = 75th centile of controls. Since hsCRP naturally increases in pregnancy, analyses were performed with, and without, the inclusion of hsCRP in the model. RESULTS: Mean hsCRP concentrations were exceptionally high among study cases and controls (6.1 and 6.4 mg/L, respectively). When hsCRP was excluded from the model, the adjusted odds ratios for NTD were 1.9 (95% confidence interval 1.1-3.4) in the presence 1 feature of MetSyn, and 6.1 (1.1-32.9) in the presence of 2 or more features. When hsCRP was included, the respective risk estimates were attenuated to 1.6 (0.88-2.8) and 3.1 (1.2-8.3). CONCLUSION: We found about 2-fold and 6-fold higher risk for NTD in the presence 1, and 2 or more features, of the metabolic syndrome, respectively. It is not clear whether this risk is altered by the presence of a high serum hsCRP concentration.

Lack of expression of XIST from a small ring X chromosome containing the XIST locus in a girl with short stature, facial dysmorphism and developmental delay.

A 46,X,r(X) karyotype was found in a three and a half year old girl with short stature, facial dysmorphism and developmental delay. The clinical findings were consistent with the phenotype described in a limited number of patients with small ring X chromosomes lacking the XIST locus, a critical player in the process of X chromosome inactivation. Surprisingly, in our patient, fluorescent in situ hybridisation demonstrated that the XIST locus was present on the ring X. However, expression studies showed that there was no XIST transcript in peripheral blood cells, suggesting that the ring X had not been inactivated. This was confirmed by the demonstration that both of the patient's alleles for the androgen receptor gene were unmethylated, and that both of the patient's ZXDA alleles were expressed. The active nature of the ring X would presumably result in overexpression of genes that may account for the developmental delay observed for the patient. Using polymorphic markers along the X chromosome, the ring X was determined to be of paternal origin with one breakpoint in the long arm between DXS8037 and XIST and one in the short arm in Xp11.2 between DXS1126 and DXS991. To attempt to determine why the XIST gene failed to be expressed, the promoter region was sequenced and found to have a base change at the same location as a variant previously associated with nonrandom X chromosome inactivation. This mutation was not seen in over one hundred normal X chromosomes examined; however, it was observed in the paternal grandmother who did not show substantial skewing of X chromosome inactivation.

Charcot-Marie-Tooth 1B caused by expansion of a familial myelin protein zero (MPZ) gene duplication.

Charcot-Marie-Tooth (CMT) disease is a group of hereditary disorders affecting the motor and sensory nerves of the peripheral nervous system. CMT patterns of inheritance include dominant, recessive, and X-linked disorders. Charcot-Marie-Tooth disease, type 1B (CMT1B, OMIM 118200) is an autosomal dominant neuropathy caused by mutations in myelin protein zero (MPZ, OMIM 159440), a structural protein of peripheral myelin. Most causative MPZ mutations are missense sequence variants; however, recent clinical reports have described cases of CMT1B caused by increased dosage of the MPZ gene, with over-expression of the MPZ protein suspected to be causative of the disorder. We report an unusual case of early onset de novo CMT1B, caused by amplification of a familial, apparently benign, MPZ duplication.

Phenotypic and functional consequences of haploinsufficiency of genes from exocyst and retinoic acid pathway due to a recurrent microdeletion of 2p13.2.

BACKGROUND: Rare, recurrent genomic imbalances facilitate the association of genotype with abnormalities at the "whole body" level. However, at the cellular level, the functional consequences of recurrent genomic abnormalities and how they can be linked to the phenotype are much less investigated. METHOD AND RESULTS: We report an example of a functional analysis of two genes from a new, overlapping microdeletion of 2p13.2 region (from 72,140,702-72,924,626). The subjects shared intellectual disability (ID), language delay, hyperactivity, facial asymmetry, ear malformations, and vertebral and/or craniofacial abnormalities. The overlapping region included two genes, EXOC6B and CYP26B1, which are involved in exocytosis/Notch signaling and retinoic acid (RA) metabolism, respectively, and are of critical importance for early morphogenesis, symmetry as well as craniofacial, skeleton and brain development. The abnormal function of EXOC6B was documented in patient lymphoblasts by its reduced expression and with perturbed expression of Notch signaling pathway genes HES1 and RBPJ, previously noted to be the consequence of EXOC6B dysfunction in animal and cell line models. Similarly, the function of CYP26B1 was affected by the deletion since the retinoic acid induced expression of this gene in patient lymphoblasts was significantly lower compared to controls (8% of controls). CONCLUSION: Haploinsufficiency of CYP26B1 and EXOC6B genes involved in retinoic acid and exocyst/Notch signaling pathways, respectively, has not been reported previously in humans. The developmental anomalies and phenotypic features of our subjects are in keeping with the dysfunction of these genes, considering their known role. Documenting their dysfunction at the cellular level in patient cells enhanced our understanding of biological processes which contribute to the clinical phenotype.

Standardized Procedural Practices of the Ontario Prenatal Screening Program for aneuploidies and open neural tube defects.

BACKGROUND/OBJECTIVES: The Ontario Prenatal Screening Program (OPSP) follows internationally recognized standardized procedures for laboratories and genetics clinics. However, it has been found that some procedures are subject to interpretation, so the current procedures are designed to facilitate a unified approach in the interpretation of literature recommendations. In Ontario, the OPSP offers multiple screening modalities with integrated prenatal screening (including both first and second trimester markers) being the most commonly chosen option. Other screening modalities include first trimester screening, second trimester quad screening, serum integrated screening, and NT-Quad. METHODS: The standardization was based on a literature review and on current practices in Ontario. RESULTS/DISCUSSION: The main finding of the review was a paucity of published data relating to the procedures and the decision-making processes involved in prenatal screening. The purpose of this publication is to provide the most up-to-date and pertinent information for clinical laboratory professionals involved with prenatal screening for Down syndrome, trisomy 18 and open neural tube defects.

Mutations in FAM134B, encoding a newly identified Golgi protein, cause severe sensory and autonomic neuropathy.

Hereditary sensory and autonomic neuropathy type II (HSAN II) leads to severe mutilations because of impaired nociception and autonomic dysfunction. Here we show that loss-of-function mutations in FAM134B, encoding a newly identified cis-Golgi protein, cause HSAN II. Fam134b knockdown results in structural alterations of the cis-Golgi compartment and induces apoptosis in some primary dorsal root ganglion neurons. This implicates FAM134B as critical in long-term survival of nociceptive and autonomic ganglion neurons.

Submicroscopic deletions of 11q24-25 in individuals without Jacobsen syndrome: re-examination of the critical region by high-resolution array-CGH.

BACKGROUND: Jacobsen syndrome is a rare contiguous gene disorder that results from a terminal deletion of the long arm of chromosome 11. It is typically characterized by intellectual disability, a variety of physical anomalies and a distinctive facial appearance. The 11q deletion has traditionally been identified by routine chromosome analysis. Array-based comparative genomic hybridization (array-CGH) has offered new opportunities to identify and refine chromosomal abnormalities in regions known to be associated with clinical syndromes. RESULTS: Using the 1 Mb BAC array (Spectral Genomics), we screened 70 chromosomally normal children with idiopathic intellectual disability (ID) and congenital abnormalities, and identified five cases with submicroscopic abnormalities believed to contribute to their phenotypes. Here, we provide detailed molecular cytogenetic descriptions and clinical presentation of two unrelated subjects with de novo submicroscopic deletions within chromosome bands 11q24-25. In subject 1 the chromosome rearrangement consisted of a 6.18 Mb deletion (from 128.25-134.43 Mb) and an adjacent 5.04 Mb duplication (from 123.15-128.19 Mb), while in subject 2, a 4.74 Mb interstitial deletion was found (from 124.29-129.03 Mb). Higher resolution array analysis (385 K Nimblegen) was used to refine all breakpoints. Deletions of the 11q24-25 region are known to be associated with Jacobsen syndrome (JBS: OMIM 147791). However, neither of the subjects had the typical features of JBS (trigonocephaly, platelet disorder, heart abnormalities). Both subjects had ID, dysmorphic features and additional phenotypic abnormalities: subject 1 had a kidney abnormality, bilateral preauricular pits, pectus excavatum, mild to moderate conductive hearing loss and behavioral concerns; subject 2 had macrocephaly, an abnormal MRI with delayed myelination, fifth finger shortening and squaring of all fingertips, and sensorineural hearing loss. CONCLUSION: Two individuals with ID who did not have the typical clinical features of Jacobsen syndrome were found to have deletions within the JBS region at 11q24-25. Their rearrangements facilitate the refinement of the JBS critical region and suggest that a) deletion of at least 3 of the 4 platelet function critical genes (ETS-1, FLI-1 and NFRKB and JAM3) is necessary for thrombocytopenia; b) one of the critical regions for heart abnormalities (conotruncal heart defects) may lie within 129.03 - 130.6 Mb; c) deletions of KCNJ1 and ADAMTS15 may contribute to the renal anomalies in Jacobsen Syndrome; d) the critical region for MRI abnormalities involves a region from 124.6 - 129.03 Mb. Our results reiterate the benefits of array-CGH for description of new phenotype/genotype associations and refinement of previously established ones.

Vitamin B12 and the risk of neural tube defects in a folic-acid-fortified population.

BACKGROUND: Low maternal vitamin B(12) status may be a risk factor for neural tube defects (NTDs). Prior studies used relatively insensitive measures of B(12), did not adjust for folate levels, and were conducted in countries without folic acid food fortification. In Canada, flour has been fortified with folic acid since mid-1997. METHODS: We completed a population-based case-control study in Ontario. We measured serum holotranscobalamin (holoTC), a sensitive indicator of B(12) status, at 15 to 20 weeks' gestation. There were 89 women with an NTD and 422 unaffected pregnant controls. A low serum holoTC was defined as less than 55.3 pmol/L, the bottom quartile value in the controls. RESULTS: The geometric mean serum holoTC levels were 67.8 pmol/L in cases and 81.2 pmol/L in controls. There was a trend of increasing risk with lower levels of holoTC, reaching an adjusted odds ratio of 2.9 (95% confidence interval = 1.2-6.9) when comparing the lowest versus highest quartile. CONCLUSIONS: There was almost a tripling in the risk for NTD in the presence of low maternal B(12) status, measured by holoTC. The benefits of adding synthetic B(12) to current recommendations for periconceptional folic acid tablet supplements or folic-acid-fortified foods need to be considered. It remains to be determined what fraction of NTD cases in a universally folate-fortified environment might be prevented by higher periconceptional intake of B(12).

A novel lysozyme mutation Phe57Ile associated with hereditary renal amyloidosis.

BACKGROUND: Variant forms of lysozyme, a ubiquitous bacteriolytic enzyme, are known to lead to hereditary non-neuropathic renal amyloidosis and, so far, three different mutations of the lysozyme gene have been reported. In this study, we report a novel lysozyme variant, Phe57Ile, associated with renal amyloidosis in three patients in one Italian Canadian family. METHODS: The proband was a 52-year-old woman who developed renal failure at the age of 42 years. Renal biopsy demonstrated replacement of glomeruli by amyloid. Her younger sister and her younger daughter who underwent renal transplantation also had renal amyloidosis. The proband's older daughter and her niece were in good health. To elucidate pathogenesis of this hereditary renal amyloidosis, DNA analyses of the lysozyme gene, including single strand confirmation polymorphism, direct DNA sequence, and restriction fragment length polymorphism analyses, were performed. RESULTS: DNA analyses of the lysozyme gene revealed a T to A transversion at the first position of codon 57 of the lysozyme gene in the proband, her sister, and her affected and unaffected daughters, indicating a replacement of Phe by Ile at residue 57. In addition, DNA sequencing demonstrated a C to A transversion at the second position of codon 70, denoting a replacement of Thr by Asn at residue 70, in the proband's sister and her niece. Thus, the proband's sister is compound heterozygous for the Phe57Ile and Thr70Asn alleles. CONCLUSION: Distinctive clinical features in patients of this family are nephropathy due to renal amyloidosis. Our results indicate that the novel lysozyme variant Phe57Ile is associated with renal amyloidosis in this family. From our results, a clear relation between the Thr70Asn polymorphism and renal amyloidosis could not be demonstrated.

Molecular characterization of an inherited ring (19) demonstrating ring opening.

Ring chromosomes arise following breakage in both chromosome arms and rejoining of the centric segment at the broken ends or by end-to-end fusion of the telomeres. The phenotype of ring carriers is unpredictable, and developmental abnormalities may occur even when the ring appears to be structurally balanced. This is believed to be due to mitotic instability from abnormal segregation and sister chromatid exchange in somatic cells. Although ring chromosomes usually arise as de novo events, transmittal from mosaic carriers to offspring sometimes occurs. In such cases, offspring with ring mosaicism in combination with a normal cell line remain unexplained. In this report, we used detailed molecular and cytogenetic analyses of a prenatally detected, inherited ring (19) to observe the behavior of the ring chromosome in culture, and to investigate the mechanism of inherited ring chromosome mosaicism.

Double-positive maternal serum screening results for down syndrome and open neural tube defects: An indicator for fetal structural or chromosomal abnormalities and adverse obstetric outcomes.

OBJECTIVE: The study was designed to evaluate whether double positive maternal serum screening results for Down syndrome and open neural tube defects indicate an increased risk of adverse perinatal outcome. STUDY DESIGN: A retrospective case-control study was conducted. In a cohort of 170,394 women who underwent maternal serum triple screening in Ontario, Canada, between October 1995 and September 1998, 189 women received positive screening results for both Down syndrome and neural tube defects. Each case was matched to 5 control subjects who had negative screening results for test center, maternal age, and specimen date. The risks for adverse perinatal outcomes were compared. RESULTS: Women with double-positive screening results had significantly higher risks of having fetuses with structural abnormalities (odds ratio, 14.5) and chromosomal anomalies (odds ratio, 36.3). They also had higher risks of having preeclampsia (odds ratio, 6.7), small-for-gestational age (odds ratio, 9.7), preterm delivery (odds ratio, 5.9), miscarriage, and intrauterine fetal death (odds ratio, 11.8). CONCLUSION: Double-positive maternal serum screening results are associated with fetal structural and chromosomal abnormalities and/or adverse pregnancy outcomes. Close fetal and maternal surveillance are indicated when such pregnancies are identified.