Extending the phenotypes associated with TRIO gene variants in a cohort of 25 patients and review of the literature.

The TRIO gene encodes a rho guanine exchange factor, the function of which is to exchange GDP to GTP, and hence to activate Rho GTPases, and has been described to impact neurodevelopment. Specific genotype-to-phenotype correlations have been established previously describing striking differentiating features seen in variants located in specific domains of the TRIO gene that are associated with opposite effects on RAC1 activity. Currently, 32 cases with a TRIO gene alteration have been published in the medical literature. Here, we report an additional 25, previously unreported individuals who possess heterozygous TRIO variants and we review the literature. In addition, functional studies were performed on the c.4394A > G (N1465S) and c.6244-2A > G TRIO variants to provide evidence for their pathogenicity. Variants reported by the current study include missense variants, truncating nonsense variants, and an intragenic deletion. Clinical features were previously described and included developmental delay, learning difficulties, microcephaly, macrocephaly, seizures, behavioral issues (aggression, stereotypies), skeletal problems including short, tapering fingers and scoliosis, dental problems (overcrowding/delayed eruption), and variable facial features. Here, we report clinical features that have not been described previously, including specific structural brain malformations such as abnormalities of the corpus callosum and ventriculomegaly, additional psychological and dental issues along with a more recognizable facial gestalt linked to the specific domains of the TRIO gene and the effect of the variant upon the function of the encoded protein. This current study further strengthens the genotype-to-phenotype correlation that was previously established and extends the range of phenotypes to include structural brain abnormalities, additional skeletal, dental, and psychiatric issues.

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.

Effect of mild hepatic or renal impairment on maternal serum screening biochemical measures.

BACKGROUND: Integrated maternal serum screening (MSS) is commonly used to screen for fetal trisomies and neural tube defects in early pregnancy. The kidney and liver each play an important role in hormone metabolism, and anecdotal data suggest that MSS biochemical measures may vary with a mother's health status. We examined the correlations between kidney and liver function parameters and MSS markers and the possible association of mild renal or hepatic impairment with MSS measures. METHODS: We completed a prospective cross-sectional study of 257 consecutive women who underwent integrated MSS at a single hospital. Serum analytes (pregnancy associated plasma protein A [PAPP-A], hCG, creatinine [Cr], and alanine aminotransferase [ALT]) were drawn at approximately 12 weeks' gestation, and alpha-fetoprotein and unconjugated estriol were drawn at 16 weeks' gestation. Creatinine clearance was calculated using the Cockcroft-Gault formula. Abnormally elevated serum Cr and ALT were each defined as ≥ 90th percentile among all women. A low creatinine clearance (CrCl) was set at ≤ 10th percentile. RESULTS: Serum hCG, PAPP-A, and alpha-fetoprotein were negatively correlated with CrCl, but not after correction for maternal age, weight, and ethnicity. No association between MSS and serum ALT was observed. The median serum concentrations of both PAPP-A (P = 0.04) and alpha-fetoprotein (P = 0.02) were significantly higher among those whose CrCl was ≤ 10th percentile. At the more extreme concentrations of PAPP-A and alpha-fetoprotein, no significant association with a low CrCl or an elevated serum ALT was seen. CONCLUSIONS: Among a group of apparently healthy pregnant women, mild renal or hepatic impairment had little or no significant correlation with individual MSS markers. Further work should focus on the effect of more severe renal or hepatic dysfunction on MSS measures.

Fragile X testing in obstetrics and gynaecology in Canada.

OBJECTIVE: To provide Canadian family physicians, genetic counsellors, medical geneticists, midwives, and obstetrician-gynaecologists with recommendations regarding screening for fragile X in the obstetrical and gynaecological population. METHODS: Medline, the Cochrane Library, journals, and textbooks were searched for English-language articles, published between 1966 and March 2008, relating to fragile X testing outcomes. Search terms included fragile X, screening, prenatal testing, pregnancy outcome, premutation, trinucleotide repeats, and ovarian failure. All study types were reviewed. Randomized controlled trial results were considered evidence of the highest quality, followed by results of cohort studies. Key individual studies on which the recommendations are based are referenced. Supporting data for each recommendation are summarized with evaluative comments and references. This document represents an abstraction of the information. EVIDENCE: The quality of evidence reported in this document has been described using the criteria outlined in the report of the Canadian Task Force on Preventive Health Care. RECOMMENDATIONS: 1. Any testing for fragile X syndrome must occur only following thorough counselling and with the informed consent of the woman to be tested. (III-A) 2. Fragile X testing is indicated for a woman with a family history of fragile X syndrome, fragile X tremor/ataxia syndrome, or premature ovarian failure (in more than one family member) if the pedigree structure indicates that she is at risk of inheriting the mutated gene. Referral to a medical geneticist for counselling and assessment should be considered in these cases. (II-2A) 3. Fragile X testing is indicated for women who have a personal history of autism or mental retardation/developmental delay of an unknown etiology or who have at least one male relative with these conditions within a three-generation pedigree. (II-2A) 4. Fragile X testing is indicated for women who have reproductive or fertility problems associated with an elevated level of follicle stimulating hormone before the age of 40. (III-A) 5. Prenatal fetal testing via chorionic villus sampling or amniocentesis should be offered to women who are confirmed to be carriers of a premutation or full mutation of the fragile X gene (FMR-1). (II-2A) Pre-implantation genetic diagnosis is available as another reproductive option. (III-A) 6. Population screening for fragile X syndrome for all women in the reproductive age-range is feasible. However, it should be considered only when there is a provincial/regional program that can test and adequately counsel the targeted population about the meaning and implications of the results. (II-2B).

Maternal obesity and the risk of placental vascular disease.

INTRODUCTION: While elevated maternal weight in early pregnancy is associated with a higher rate of preeclampsia, the risk of placental abruption and placental infarction is unknown. METHODS: We evaluated the risk of placental abruption, placental infarction, and preeclampsia in association with maternal weight quintile at approximately 17 weeks' gestation in 386 323 women with a singleton pregnancy who underwent maternal serum screening in Ontario. RESULTS: After adjusting for age, ethnicity, parity, diabetes mellitus, and tobacco use, the odds ratio (OR) for preeclampsia was 4.1 (95% confidence interval [CI] 3.8-4.4) comparing the highest and lowest weight quintiles. Conversely, there was a lower risk of placental abruption or placental infarction, despite further adjustment for preeclampsia, gestational hypertension and drug dependence (OR 0.81, 95% CI 0.75-0.87). CONCLUSION: Higher maternal weight in early pregnancy is associated with a higher risk of preeclampsia and a lower risk of placental abruption or placental infarction, a seeming paradox that requires further elucidation.

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.

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).

The identification of risk of spontaneous fetal loss through second-trimester maternal serum screening.

OBJECTIVE: The purpose of this study was to investigate associations between risk of spontaneous fetal loss and risk estimates for Down syndrome, trisomy 18, and neural tube defects assigned by second-trimester maternal serum screening. STUDY DESIGN: The study involved 264,653 women with available pregnancy outcomes who were screened between 15 and 20 weeks of gestation in the Ontario Maternal Serum Screening Program between October 1995 and September 2000. Pregnancies complicated by fetal chromosomal or structural abnormalities, insulin-dependent diabetes mellitus, and multiple pregnancies were excluded. Spontaneous fetal loss was defined as spontaneous miscarriage and intrauterine fetal demise as classified by the ICD-9 system, but including only those > or = 15 weeks of gestation. Women were grouped according to risk estimates for Down syndrome, trisomy 18, and neural tube defects, respectively. Spontaneous fetal loss rates by each risk group were evaluated after adjusting for losses associated with maternal age and amniocentesis. RESULTS: Fetal loss rates increased in women with risk estimates of > or = 1 in 1110 for trisomy 18 or neural tube defects, and > or = 1 in 130 for Down syndrome. The excessive fetal loss rates for these 3 groups of women were 14.4%, 3.2%, and 1.5% respectively. CONCLUSION: Fetal loss rate markedly increased in women with high-risk estimates for trisomy 18, neural tube defects, and Down syndrome. Risk estimates assigned by triple marker screening may provide an early means of stratifying pregnancies into risk for fetal loss.

Greater maternal weight and the ongoing risk of neural tube defects after folic acid flour fortification.

OBJECTIVE: Maternal obesity is likely a risk factor for neural tube defects (NTDs). By late 1997, it became mandatory in Canada that all refined wheat flour be fortified with folic acid. Because overweight women may consume greater quantities of refined wheat flour, we questioned whether their risk of NTD changed after flour fortification. METHODS: A retrospective population-based study was conducted between 1994 and late 2000. We included all Ontarian women who underwent antenatal maternal screening at 15 to 20 weeks of gestation. Self-declared maternal date of birth, ethnicity, current weight, and the presence of pregestational diabetes mellitus were recorded in a standardized fashion on the maternal screening requisition sheet. The presence of NTDs was systematically detected both antenatally and postnatally. The risk of open NTD was evaluated across maternal weight quartiles and deciles, and an interaction between greater maternal weight and the presence of flour fortification was tested using multiple logistic regression analysis. RESULTS: A total of 292 open NTDs were detected among 420,362 women. The adjusted odds ratio (OR) for NTD was 1.2 (95% confidence interval [CI] 1.1-1.3) per 10-kg incremental rise in maternal weight. Comparing the highest with the lowest quartile of maternal weight, the adjusted OR for NTD was 2.6 (95% CI 1.8-4.0). A similar finding was observed for the highest compared with lowest weight deciles (adjusted OR 3.3, 95% CI 1.7-6.2). The interaction between elevated maternal weight and the presence of folic acid flour fortification was of borderline significance (P = .09). Before fortification, greater maternal weight was associated with a modestly increased risk of NTD (adjusted OR 1.4, 95% CI 1.0-1.8); after flour fortification, this effect was more pronounced (adjusted OR 2.8, 95% CI 1.2-6.6). CONCLUSION: These data emphasize the higher risk of NTD associated with increased maternal weight, even after universal folic acid flour fortification. Beyond periconceptional folic acid use, consideration should be given to testing whether prepregnancy weight reduction is an independent means of preventing NTD. LEVEL OF EVIDENCE: II-2.

Age-specific risk of fetal loss observed in a second trimester serum screening population.

OBJECTIVE: The purpose of this study was to investigate age-specific spontaneous fetal loss rates of pregnancies without known chromosomal or structural abnormalities from mid-second trimester onward. STUDY DESIGN: The study consisted of 264,653 women screened between October 1995 and September 2000 with available pregnancy outcomes. Pregnancies associated with fetal chromosomal or structural abnormalities, insulin dependent diabetes mellitus, and multiple pregnancies were excluded. Spontaneous fetal losses at or after 15 weeks of gestation were identified. Women were grouped according to maternal age at expected date of delivery. Spontaneous fetal loss rates in each group were evaluated after adjusting fetal losses associated with amniocentesis and identifiable ethnic groups. RESULTS: Fetal loss rates increased in both younger and older women. The lowest rate was seen in women at mid-20s. Compared with Caucasian and Asian women, black women had higher fetal loss rate at nearly every age group. CONCLUSION: The results of the study provided a baseline age-specific spontaneous fetal loss rate of pregnancies at a specified gestational window.

Maternal ethnicity and risk of neural tube defects: a population-based study.

BACKGROUND: Maternal body mass and the presence of diabetes mellitus are probable risk factors for neural tube defects (NTDs). The association between maternal ethnicity and the risk of NTDs remains poorly understood, however. METHODS: We performed a retrospective population-based study and included all women in Ontario who underwent antenatal maternal screening (MSS) at 15 to 20 weeks' gestation between 1994 and late 2000. Self-declared maternal date of birth, ethnicity and weight and the presence of pregestational diabetes mellitus were recorded in a standardized fashion on the MSS requisition sheet. NTDs were detected antenatally by ultrasonography or fetal autopsy and postnatally by considering all live and stillborn affected infants beyond 20 weeks' gestation. The risk of open NTD was evaluated across the 5 broad ethnic groups used for MSS, with white ethnicity as the referent. RESULTS: Compared with white women (n = 290 799), women of First Nations origin (n = 1551) were at increased associated risk of an NTD-affected pregnancy (adjusted odds ratio [OR] 5.2, 95% confidence interval [CI] 2.1-12.9). Women of other ethnic origins were not at increased associated risk compared with white women (women of Asian origin [n = 75 590]: adjusted OR 0.9, 95% CI 0.6-1.3; black women [n = 25 966]: adjusted OR 0.6, 95% CI 0.3-1.1; women of "other" ethnic origin [n = 10 009]: adjusted OR 0.1, 95% CI 0.02-0.9). INTERPRETATION: The associated risk of NTD-affected pregnancies was higher among women of First Nations origin than among women of other ethnic origins. The mechanisms for this discrepancy should be explored.

Association between folic acid food fortification and congenital orofacial clefts.

By January 1998, most of Canada's cereal grain products were being fortified with folic acid. Among 336963 women who underwent antenatal maternal serum screening, the prevalence of orofacial clefts did not change from before (1.15 per 1000) to after (1.21 per 1000) food fortification (prevalence ratio, 1.06; 95% confidence interval, 0.86-1.30).

Prevalence of trisomy 21 following folic acid food fortification.

Polymorphisms of maternal genes responsible for normal folate metabolism may be associated with an increased risk of fetal trisomy 21. By January 1998, most of Canada's flour was being fortified with folic acid. We investigated whether the prevalence of antenatally and postnatally detected trisomy 21 changed before and after folic acid food fortification. A total of 218,977 women underwent second trimester maternal serum screening for trisomy 21 in the 48 months before fortification and 117,986 women were screened in the 29 months after fortification. There were 375 identified cases of trisomy 21 before fortification (1.71 per 1,000), compared to 201 cases thereafter (1.70 per 1,000) for a crude prevalence ratio (PR) of 0.99 (95% confidence interval [CI] 0.84-1.18). The associated risk of trisomy 21 did not change after adjustment for mean maternal age (adjusted PR 0.99 [95% CI 0.82-1.19]). Similarly, no significant decline in the monthly prevalence of trisomy 21 was observed using autoregressive integrated moving average time series analysis (P = 0.24). In conclusion, we failed to observe a decline in the occurrence of trisomy 21 following folic acid food fortification.

Accuracy of trisomy 18 screening using the second-trimester triple test.

OBJECTIVE: To assess the accuracy of the calculated risk for trisomy 18 assigned to individual women screened with the second-trimester triple test. METHODS: The study was based on 382598 women screened in the Ontario Maternal Serum Screening Programme between October 1993 and September 2000. Of the women screened, 111 cases of trisomy 18 were identified. Originally, 92874 women were screened using a risk cut-off level method. Estimated risks of trisomy 18 were calculated by applying published population parameters for the remaining women screened using a fixed analyte cut-off method. Women were ranked according to their individual risk for trisomy 18 syndrome in decreasing order and divided into 12 groups. The mean calculated risks of having an affected pregnancy at term for each group were compared with the birth prevalence of the corresponding group after allowing for spontaneous fetal losses. RESULTS: Agreement between the mean calculated risks and the observed prevalence was seen across the entire risk range, although women identified as having high-risk pregnancies had an actual prevalence that was somewhat lower than that estimated by the screen. CONCLUSION: The calculated risk for trisomy 18 syndrome assigned to the individual woman on the basis of the risk cut-off method accurately reflects their risk of having a term trisomy 18 syndrome pregnancy.

The implications of a false positive second-trimester serum screen for Down syndrome.

OBJECTIVE: To investigate the genetic and obstetric implications of false positive Down syndrome serum screening results. METHODS: The study population comprised 162774 women underwent triple marker screening in the Ontario Maternal Serum Screening program between October 1995 and September 1998, with outcomes obtained from the Canadian Institute of Health Information. The study compares the incidence of chromosomal abnormalities other than Down syndrome in screen positive women with background incidence from the literature. It also compares the risks of having a fetus with congenital abnormalities or of developing obstetric complications in 11549 screen positive women with their matched controls. RESULTS: A higher incidence of trisomy 13 (12.4 per 10000) was seen in screen positive women; the incidence of other chromosomal abnormalities in screen positive women was not increased relative to the general population. The higher incidence of trisomy 13 may have been biased by the selective uptake of amniocentesis in women who had high risks for Down syndrome or abnormal ultrasound findings. Incidences of fetal congenital abnormality in screen positive and negative women were similar. Women who screened positive for Down syndrome had increased risk of spontaneous fetal loss (odds ratio 1.80; 95% confidence interval 1.54, 2.07) but no other obstetric complications. CONCLUSION: Among women who screened positive for Down syndrome, we found a higher number of spontaneous fetal losses and a possibly higher risk of having a fetus with trisomy 13. We did not find an increased risk for other chromosomal abnormalities, congenital abnormalities, or other adverse obstetric outcomes.