The Role of cfDNA Biomarkers and Patient Data in the Early Prediction of Preeclampsia: Artificial Intelligence Model.

OBJECTIVE: Accurate individualized assessment of preeclampsia risk enables the identification of patients most likely to benefit from initiation of low-dose aspirin at 12-16 weeks' gestation when there is evidence for its effectiveness, as well as guiding appropriate pregnancy care pathways and surveillance. The primary objective of this study was to evaluate the performance of artificial neural network models for the prediction of preterm preeclampsia (<37 weeks' gestation) using patient characteristics available at the first antenatal visit and data from prenatal cell-free DNA (cfDNA) screening. Secondary outcomes were prediction of early onset preeclampsia (<34 weeks' gestation) and term preeclampsia (≥37 weeks' gestation). METHODS: This secondary analysis of a prospective, multicenter, observational prenatal cfDNA screening study (SMART) included singleton pregnancies with known pregnancy outcomes. Thirteen patient characteristics that are routinely collected at the first prenatal visit and two characteristics of cfDNA, total cfDNA and fetal fraction (FF), were used to develop predictive models for early-onset (<34 weeks), preterm (<37 weeks), and term (≥37 weeks) preeclampsia. For the models, the 'reference' classifier was a shallow logistic regression (LR) model. We also explored several feedforward (non-linear) neural network (NN) architectures with one or more hidden layers and compared their performance with the LR model. We selected a simple NN model built with one hidden layer and made up of 15 units. RESULTS: Of 17,520 participants included in the final analysis, 72 (0.4%) developed early onset, 251 (1.4%) preterm, and 420 (2.4%) term preeclampsia. Median gestational age at cfDNA measurement was 12.6 weeks and 2,155 (12.3%) had their cfDNA measurement at 16 weeks' gestation or greater. Preeclampsia was associated with higher total cfDNA (median 362.3 versus 339.0 copies/ml cfDNA; p<0.001) and lower FF (median 7.5% versus 9.4%; p<0.001). The expected, cross-validated area under the curve (AUC) scores for early onset, preterm, and term preeclampsia were 0.782, 0.801, and 0.712, respectively for the LR model, and 0.797, 0.800, and 0.713, respectively for the NN model. At a screen-positive rate of 15%, sensitivity for preterm preeclampsia was 58.4% (95% CI 0.569, 0.599) for the LR model and 59.3% (95% CI 0.578, 0.608) for the NN model.The contribution of both total cfDNA and FF to the prediction of term and preterm preeclampsia was negligible. For early-onset preeclampsia, removal of the total cfDNA and FF features from the NN model was associated with a 6.9% decrease in sensitivity at a 15% screen positive rate, from 54.9% (95% CI 52.9-56.9) to 48.0% (95% CI 45.0-51.0). CONCLUSION: Routinely available patient characteristics and cfDNA markers can be used to predict preeclampsia with performance comparable to other patient characteristic models for the prediction of preterm preeclampsia. Both LR and NN models showed similar performance.

Performance of prenatal cfDNA screening for sex chromosomes.

PURPOSE: The aim of this study was to assess the performance of cell-free DNA (cfDNA) screening to detect sex chromosome aneuploidies (SCAs) in an unselected obstetrical population with genetic confirmation. METHODS: This was a planned secondary analysis of the multicenter, prospective SNP-based Microdeletion and Aneuploidy RegisTry (SMART) study. Patients receiving cfDNA results for autosomal aneuploidies and who had confirmatory genetic results for the relevant sex chromosomal aneuploidies were included. Screening performance for SCAs, including monosomy X (MX) and the sex chromosome trisomies (SCT: 47,XXX; 47,XXY; 47,XYY) was determined. Fetal sex concordance between cfDNA and genetic screening was also evaluated in euploid pregnancies. RESULTS: A total of 17,538 cases met inclusion criteria. Performance of cfDNA for MX, SCTs, and fetal sex was determined in 17,297, 10,333, and 14,486 pregnancies, respectively. Sensitivity, specificity, and positive predictive value (PPV) of cfDNA were 83.3%, 99.9%, and 22.7% for MX and 70.4%, 99.9%, and 82.6%, respectively, for the combined SCTs. The accuracy of fetal sex prediction by cfDNA was 100%. CONCLUSION: Screening performance of cfDNA for SCAs is comparable to that reported in other studies. The PPV for the SCTs was similar to the autosomal trisomies, whereas the PPV for MX was substantially lower. No discordance in fetal sex was observed between cfDNA and postnatal genetic screening in euploid pregnancies. These data will assist interpretation and counseling for cfDNA results for sex chromosomes.

Multidisciplinary management of a pregnancy complicated by Glanzmann thrombasthenia: A case report.

BACKGROUND: Glanzmann thrombasthenia (GT) is a rare, autosomal recessive disorder of platelet glycoprotein IIb-IIIa receptors. Pregnant patients with GT are at increased risk of maternal and fetal bleeding. There is a paucity of literature on the peripartum management of patients. CASE DESCRIPTION: We present the antepartum through the postpartum course of a patient with GT who was managed by a multidisciplinary approach that included communication across maternal-fetal medicine, hematology, transfusion medicine, and anesthesiology services. In addition to routine prepartum obstetric imaging and hematologic laboratory studies, we proactively monitored the patient for anti-platelet antibodies every 4-6 weeks to gauge the risk for neonatal alloimmune thrombocytopenia. Furthermore, we prioritized uterotonics, tranexamic acid, and transfusion of HLA-matched platelets to manage bleeding for mother and fetus intrapartum through the postpartum periods. CONCLUSION: To date, there are limited guidelines for managing bleeding or preventing alloimmunization during pregnancy in patients with GT. Here, we present a complex case with aggressive management of bleeding prophylactically for the mother while serially monitoring both mother and fetus for peripartum bleeding risks and events. Moreover, future studies warrant continued evaluation of these approaches to mitigate increased bleeding risks in subsequent pregnancies.

Obstetrical, perinatal, and genetic outcomes associated with nonreportable prenatal cell-free DNA screening results.

BACKGROUND: The clinical implications of nonreportable cell-free DNA screening results are uncertain, but such results may indicate poor placental implantation in some cases and be associated with adverse obstetrical and perinatal outcomes. OBJECTIVE: This study aimed to assess the outcomes of pregnancies with nonreportable cell-free DNA screening in a cohort of patients with complete genetic and obstetrical outcomes. STUDY DESIGN: This was a prespecified secondary analysis of a multicenter prospective observational study of prenatal cell-free DNA screening for fetal aneuploidy and 22q11.2 deletion syndrome. Participants who underwent cell-free DNA screening from April 2015 through January 2019 were offered participation. Obstetrical outcomes and neonatal genetic testing results were collected from 21 primary-care and referral centers in the United States, Europe, and Australia. The primary outcome was risk for adverse obstetrical and perinatal outcomes (aneuploidy, preterm birth at <28, <34, and <37 weeks' gestation, preeclampsia, small for gestational age or birthweight <10th percentile for gestational week, and a composite outcome that included preterm birth at <37 weeks, preeclampsia, small for gestational age, and stillbirth at >20 weeks) after nonreportable cell-free DNA screening because of low fetal fraction or other causes. Multivariable analyses were performed, adjusting for variables known to be associated with obstetrical and perinatal outcomes, nonreportable results, or fetal fraction. RESULTS: In total, 25,199 pregnant individuals were screened, and 20,194 were enrolled. Genetic confirmation was missing in 1165 (5.8%), 1085 (5.4%) were lost to follow-up, and 93 (0.5%) withdrew; the final study cohort included 17,851 (88.4%) participants who had cell-free DNA, fetal or newborn genetic confirmatory testing, and obstetrical and perinatal outcomes collected. Results were nonreportable in 602 (3.4%) participants. A sample was redrawn and testing attempted again in 427; in 112 (26.2%) participants, results were again nonreportable. Nonreportable results were associated with higher body mass index, chronic hypertension, later gestational age, lower fetal fraction, and Black race. Trisomy 13, 18, or 21 was confirmed in 1.6% with nonreportable tests vs 0.7% with reported results (P=.013). Rates of preterm birth at <28, 34, and 37 weeks, preeclampsia, and the composite outcome were higher among participants with nonreportable results, and further increased among those with a second nonreportable test, whereas the rate of small for gestational age infants was not increased. After adjustment for confounders, the adjusted odds ratios were 2.2 (95% confidence interval, 1.1-4.4) and 2.6 (95% confidence interval, 0.6-10.8) for aneuploidy, and 1.5 (95% confidence interval, 1.2-1.8) and 2.1 (95% confidence interval, 1.4-3.2) for the composite outcome after a first and second nonreportable test, respectively. Of the patients with nonreportable tests, 94.9% had a live birth, as opposed to 98.8% of those with reported test results (adjusted odds ratio for livebirth, 0.20 [95% confidence interval, 0.13-0.30]). CONCLUSION: Patients with nonreportable cell-free DNA results are at increased risk for a number of adverse outcomes, including aneuploidy, preeclampsia, and preterm birth. They should be offered diagnostic genetic testing, and clinicians should be aware of the increased risk of pregnancy complications.

Impact of high-risk prenatal screening results for 22q11.2 deletion syndrome on obstetric and neonatal management: Secondary analysis from the SMART study.

OBJECTIVE: One goal of prenatal genetic screening is to optimize perinatal care and improve infant outcomes. We sought to determine whether high-risk cfDNA screening for 22q11.2 deletion syndrome (22q11.2DS) affected prenatal or neonatal management. METHODS: This was a secondary analysis from the SMART study. Patients with high-risk cfDNA results for 22q11.2DS were compared with the low-risk cohort for pregnancy characteristics and obstetrical management. To assess differences in neonatal care, we compared high-risk neonates without prenatal genetic confirmation with a 1:1 matched low-risk cohort. RESULTS: Of 18,020 eligible participants enrolled between 2015 and 2019, 38 (0.21%) were high-risk and 17,982 (99.79%) were low-risk for 22q11.2DS by cfDNA screening. High-risk participants had more prenatal diagnostic testing (55.3%; 21/38 vs. 2.0%; 352/17,982, p < 0.001) and fetal echocardiography (76.9%; 10/13 vs. 19.6%; 10/51, p < 0.001). High-risk newborns without prenatal diagnostic testing had higher rates of neonatal genetic testing (46.2%; 6/13 vs. 0%; 0/51, P < 0.001), echocardiography (30.8%; 4/13 vs. 4.0%; 2/50, p = 0.013), evaluation of calcium levels (46.2%; 6/13 vs. 4.1%; 2/49, P < 0.001) and lymphocyte count (53.8%; 7/13 vs. 15.7%; 8/51, p = 0.008). CONCLUSIONS: High-risk screening results for 22q11.2DS were associated with higher rates of prenatal and neonatal diagnostic genetic testing and other 22q11.2DS-specific evaluations. However, these interventions were not universally performed, and >50% of high-risk infants were discharged without genetic testing, representing possible missed opportunities to improve outcomes for affected individuals.

Cell-free DNA screening for prenatal detection of 22q11.2 deletion syndrome.

BACKGROUND: Historically, prenatal screening has focused primarily on the detection of fetal aneuploidies. Cell-free DNA now enables noninvasive screening for subchromosomal copy number variants, including 22q11.2 deletion syndrome (or DiGeorge syndrome), which is the most common microdeletion and a leading cause of congenital heart defects and neurodevelopmental delay. Although smaller studies have demonstrated the feasibility of screening for 22q11.2 deletion syndrome, large cohort studies with confirmatory postnatal testing to assess test performance have not been reported. OBJECTIVE: This study aimed to assess the performance of single-nucleotide polymorphism-based, prenatal cell-free DNA screening for detection of 22q11.2 deletion syndrome. STUDY DESIGN: Patients who underwent single-nucleotide polymorphism-based prenatal cell-free DNA screening for 22q11.2 deletion syndrome were prospectively enrolled at 21 centers in 6 countries. Prenatal or newborn DNA samples were requested in all cases for genetic confirmation using chromosomal microarrays. The primary outcome was sensitivity, specificity, positive predictive value, and negative predictive value of cell-free DNA screening for the detection of all deletions, including the classical deletion and nested deletions that are ≥500 kb, in the 22q11.2 low-copy repeat A-D region. Secondary outcomes included the prevalence of 22q11.2 deletion syndrome and performance of an updated cell-free DNA algorithm that was evaluated with blinding to the pregnancy outcome. RESULTS: Of the 20,887 women enrolled, a genetic outcome was available for 18,289 (87.6%). A total of 12 22q11.2 deletion syndrome cases were confirmed in the cohort, including 5 (41.7%) nested deletions, yielding a prevalence of 1 in 1524. In the total cohort, cell-free DNA screening identified 17,976 (98.3%) cases as low risk for 22q11.2 deletion syndrome and 38 (0.2%) cases as high risk; 275 (1.5%) cases were nonreportable. Overall, 9 of 12 cases of 22q11.2 were detected, yielding a sensitivity of 75.0% (95% confidence interval, 42.8-94.5); specificity of 99.84% (95% confidence interval, 99.77-99.89); positive predictive value of 23.7% (95% confidence interval, 11.44-40.24), and negative predictive value of 99.98% (95% confidence interval, 99.95-100). None of the cases with a nonreportable result was diagnosed with 22q11.2 deletion syndrome. The updated algorithm detected 10 of 12 cases (83.3%; 95% confidence interval, 51.6-97.9) with a lower false positive rate (0.05% vs 0.16%; P<.001) and a positive predictive value of 52.6% (10/19; 95% confidence interval, 28.9-75.6). CONCLUSION: Noninvasive cell-free DNA prenatal screening for 22q11.2 deletion syndrome can detect most affected cases, including smaller nested deletions, with a low false positive rate.

Implementation of an Enhanced Prenatal Checklist to Increase Rates of Counseling of Prenatal Fetal Aneuploidy Testing.

Aim This study aims to assess the effect of implementing an enhanced prenatal genetic checklist to guide the provider's discussion on both screening and diagnostic options for fetal aneuploidy testing at the initial prenatal visit. Methods A retrospective quality improvement (QI) project was performed at a single, large, urban academic medical center. The implementation of this project was prospective; however, data was examined retrospectively after the QI initiative was implemented for three months. Patients were included if they were less than 24 weeks gestational age with a live intrauterine gestation at their initial obstetric (OB) visit. Patients less than 18 years old at the initial OB visit were excluded. The results were analyzed using the statistical software R. Chi-squared tests were used to examine proportional differences between the pre- and post-intervention groups with respect to demographic and clinical characteristics and documented genetic counseling discussions. Results A total of 416 patients were included in the final cohort. As measured by documentation, the rate of discussion of diagnostic prenatal genetic testing increased significantly from the pre-intervention proportion of 54% to the post-intervention proportion of 72% (p < 0.001). In the subgroup analysis of patients with advanced maternal age, the rate of discussion of diagnostic prenatal genetic testing increased significantly from the pre-intervention proportion of 53% to the post-intervention proportion of 83% (p = 0.003), and the rate of genetics counseling referrals made at the initial prenatal visit increased significantly from 4% pre-intervention to 38% post-intervention (p < 0.001). Conclusions The use of an enhanced prenatal genetic checklist led to increased discussion of diagnostic fetal aneuploidy testing and increased rates of referral to genetics counseling.

Genetic counseling practices among outpatient obstetric providers in the Northeast.

BACKGROUND: The American College of Obstetricians and Gynecologists recommends all pregnant people be offered genetic screening and diagnostic testing regardless of risk factors. Previous studies have demonstrated disparities in referrals for genetic testing by race outside of pregnancy, but limited data exist regarding genetic counseling practices during pregnancy. OBJECTIVE: This study aimed to describe how patient, provider, and practice demographics influence the offering of diagnostic prenatal genetic testing by outpatient prenatal care providers. STUDY DESIGN: This was a multicenter anonymous survey study conducted between October 2021 and March 2022. Outpatient prenatal care providers, including family medicine and obstetrics attendings, residents, maternal-fetal medicine fellows, nurse practitioners, physician assistants, and midwives, were surveyed about their genetic counseling practices and practice demographics. The primary outcome was the proportion of respondents who answered "yes, all patients" to the survey question "Do you offer diagnostic genetic testing to all patients?" The secondary outcomes included the association between patient and practice demographics and offering diagnostic testing. Diagnostic testing was defined as chorionic villus sampling or amniocentesis. Screening genetic tests were defined as sequential screen, quadruple screen, cell-free DNA screening, or "other." The chi-square test or Fisher exact test was used as appropriate. For the outcome answers of diagnostic testing, logistic regression was performed to assess the association between the answer of diagnostic genetic testing and the current training level of providers, race and ethnicity, and insurance status variables. Multivariable analysis was performed to adjust for confounders. RESULTS: A total of 635 outpatient prenatal care providers across 7 sites were sent the survey. Overall, 419 providers responded for a total response rate of 66%. Of the providers who responded, most were attendings (44.9%), followed by residents (37.5%). Providers indicated the race, insurance status, and primary language of their patient population. Screening genetic testing was offered by 98% of providers. Per provider report, 37% offered diagnostic testing to all patients, 18% did not offer it at all, and 44% only offered it if certain patient factors were present. Moreover, 54.8% of attendings reported universally offering diagnostic testing. On univariable analysis, residents were less likely to offer diagnostic testing than attendings (odds ratio, 0.18; 95% confidence interval, 0.11-0.30). Providers who serve non-Hispanic Black, Hispanic Black, and other Hispanic patients were less likely to report offering diagnostic testing than other patient populations. Providers who served non-Hispanic Whites were more likely to offer diagnostic testing (odds ratio, 2.26; 95% confidence interval, 1.51-3.39). Patient populations who were primarily privately insured were more likely to be offered diagnostic testing compared with primarily publicly insured patients (odds ratio, 6.25; 95% confidence interval, 3.60-10.85). Providers who served a primarily English-speaking population were more likely to offer diagnostic genetic testing than other patient populations (odds ratio, 0.43; 95% confidence interval, 0.26-0.69). On multivariable analysis, the factors that remained significantly associated with offering diagnostic testing included level of training (resident odds ratio, 0.33; 95% confidence interval, 0.17-0.62; P=.0006; advanced practice provider odds ratio, 0.34; 95% confidence interval, 0.15-0.82; P=.02), having at least one-third of the patient population identify as "other Hispanic" (odds ratio, 0.42; 95% confidence interval, 0.23-0.77; P=.005), and having private insurance instead of public insurance (primarily private insured odds ratio, 2.84; 95% confidence interval, 1.20-6.74; P=.02). CONCLUSION: Although offering genetic screening and diagnostic testing to all patients is recommended, no provider group universally offers diagnostic testing. Providers who serve populations from a racial and ethnic minority, those with public insurance, and those whose primary language is not English are less likely to report universally offering diagnostic genetic testing.

The SunBEAm birth cohort: Protocol design.

Background: Food allergy (FA) and atopic dermatitis (AD) are common conditions that often present in the first year of life. Identification of underlying mechanisms and environmental determinants of FA and AD is essential to develop and implement effective prevention and treatment strategies. Objectives: We sought to describe the design of the Systems Biology of Early Atopy (SunBEAm) birth cohort. Methods: Funded by the National Institute of Allergy and Infectious Diseases (NIAID) and administered through the Consortium for Food Allergy Research (CoFAR), SunBEAm is a US population-based, multicenter birth cohort that enrolls pregnant mothers, fathers, and their newborns and follows them to 3 years. Questionnaire and biosampling strategies were developed to apply a systems biology approach to identify environmental, immunologic, and multiomic determinants of AD, FA, and other allergic outcomes. Results: Enrollment is currently underway. On the basis of an estimated FA prevalence of 6%, the enrollment goal is 2500 infants. AD is defined on the basis of questionnaire and assessment, and FA is defined by an algorithm combining history and testing. Although any FA will be recorded, we focus on the diagnosis of egg, milk, and peanut at 5 months, adding wheat, soy, cashew, hazelnut, walnut, codfish, shrimp, and sesame starting at 12 months. Sampling includes blood, hair, stool, dust, water, tape strips, skin swabs, nasal secretions, nasal swabs, saliva, urine, functional aspects of the skin, and maternal breast milk and vaginal swabs. Conclusions: The SunBEAm birth cohort will provide a rich repository of data and specimens to interrogate mechanisms and determinants of early allergic outcomes, with an emphasis on FA, AD, and systems biology.

Intravenous immunoglobulin induced pancytopenia while preventing development of gestational alloimmune liver disease: A case report.

Gestational alloimmune liver disease is a rare complication associated with reactive maternal immunoglobulins resulting in neonatal liver pathology. The mainstay treatment for prevention in future pregnancies is intravenous immunoglobulins. Although relatively well tolerated, adverse reactions may occur. In this report, we highlight a case of intravenous immunoglobulin induced pancytopenia diagnosed by exclusion after thorough work-up. The patient was counseled on options and an informed decision was made to proceed with re-trial of intravenous immunoglobulin without systemic prednisone. This resulted in the delivery of a healthy neonate. We propose that future adverse reactions to intravenous immunoglobulin in pregnancy may warrant the trial of a new medication lot and use of systemic steroids only if subsequently indicated.

Diagnosis and management of neonatal alloimmune thrombocytopenia in pregnancy.

Neonatal alloimmune thrombocytopenia (NAIT) is the most common cause of severe thrombocytopenia in the healthy newborn, occurring in 1 in 1000 live births. NAIT is analogous to rhesus alloimmunization in pathophysiology; however, it often presents unexpectedly in first pregnancies. Presentation of NAIT varies from mild thrombocytopenia to life-threatening intracranial hemorrhage. It has been observed to be more severe in subsequent affected pregnancies. It is important that the diagnosis of NAIT be considered in the work-up of all cases of neonatal thrombocytopenia to determine the risk to future pregnancies and corresponding management plans. This article discusses the pathogenesis and incidence of NAIT and the antenatal and postnatal management of this condition.

Familiality and co-occurrence of clinical features of systemic lupus erythematosus.

OBJECTIVE: To evaluate familiality of 15 clinical and laboratory features in systemic lupus erythematosus (SLE)-affected sibpairs, and to estimate correlations with the age at SLE diagnosis in affected sibpairs and parent-offspring pairs. METHODS: Concordance rates and sibling risk ratios were used as indicators of familiality for 15 manifestations of SLE. Pearson's correlations and paired t-tests were used to compare the age at SLE diagnosis in affected sibpairs and in parent-offspring pairs. RESULTS: Increased sibling risk ratios (1.9-3.9) for thrombocytopenia, discoid rash, neurologic disorder (defined as seizure or psychosis), and hemolytic anemia were observed in 159 SLE-affected sibpairs. Among these clinical features, paired expression of hemolytic anemia plus thrombocytopenia and hemolytic anemia plus neurologic disorder appeared to be more frequent in 709 SLE patients than would be expected by chance (P < 0.00001 and P < 0.007, respectively). The ratio of the presence of both hemolytic anemia and neurologic disorder was approximately 13 times higher in the younger affected sib than in the older affected sib (P < 0.02). Familiality of patient age at SLE diagnosis, as observed by relative correlations, was greater in 125 affected sibpairs (r = 0.67, P < 0.0001) than in 37 affected parent-offspring pairs (r = 0.47, P = 0.003). The median +/- SD age at SLE diagnosis was significantly lower in offspring (21.5 +/- 10.1 years) than in their parents (41.6 +/- 15.8 years) (P < 0.0001) but was not different in sibpairs. The combined non-Caucasian sibpairs had a younger mean age at SLE diagnosis compared with Caucasian sibpairs (P = 0.014). CONCLUSION: Evidence for familiality of thrombocytopenia, discoid rash, neurologic disorder, hemolytic anemia, and co-occurring neurologic disorder plus hemolytic anemia in SLE was observed in 159 affected sibpairs. Familiality of the age at SLE diagnosis in relative pairs suggests that shared genes and/or shared environmental exposures impact disease susceptibility. Shared immediate environmental triggers appear less compelling, because the average time between dates of diagnosis was 11 years in parent-offspring pairs and 7.5 years in affected sibpairs. The significantly earlier age at disease diagnosis in offspring compared with their parents suggests that some forms of anticipation might play a role in susceptibility to SLE. Stratifying families by subphenotypes that are familial may reduce heterogeneity and facilitate identification of genetic risk factors for SLE.

Linkage and interaction of loci on 1q23 and 16q12 may contribute to susceptibility to systemic lupus erythematosus.

OBJECTIVE: Six recent genome scans of different systemic lupus erythematosus (SLE) multiplex family cohorts showed multiple putative susceptibility loci. In the present study, we examined 4 previously identified loci to replicate findings of significant linkage to 1q23 and 16q12, and to support findings of suggestive linkage to 14q21-23 and 20p12 in a cohort of 115 multiethnic nuclear families containing 145 SLE-affected sibpairs. METHODS: Model-free, multipoint linkage analyses (SIBPAL2, SAGE version 4.0) and exclusion mapping (GeneHunter) were performed. RESULTS: Linkages to 1q23 (peak at D1S2675, mean allele sharing [MAS] 0.56; P = 0.003) and to 16q12 (peaks between D16S753 and D16S757, MAS 0.57; P = 0.003) were confirmed, but linkage evidence at 20p12 was weak and inconsistent (MAS 0.52-0.56; from P = 0.005 to P not significant). Evidence for linkage to 1q23 and 16q12 was stronger in 68 non-Caucasian affected sibpairs than in 77 Caucasian affected sibpairs. Exclusion mapping ruled out linkage at 14q21-23 (lambda(s) [sib recurrence risk or genotypic risk ratio] = 1.8). Because the pericentromeric region of chromosome 16 has been identified by genome scans in several autoimmune diseases, we postulated that it might harbor an autoimmune modifier gene. To explore this possibility, we tested for an interaction between 16q12 and 1q23, and between 16q12 and 20p12. Haplotype sharing at 1q23 increased concomitantly with increased haplotype sharing at 16q12 (P = 0.008 by nonparametric Jonckheere-Terpstra exact statistical test). No evidence supporting an interaction between 16q12 and 20p12 was observed. Analysis of sibpairs sharing 2 alleles at 16q12 also showed increased allele sharing at 1q23 (MAS from 0.56 to 0.65). CONCLUSION: These data support the presence of SLE susceptibility genes at 1q23 and 16q12, particularly in non-Caucasians. The skewed distribution of haplotypes suggests that genetic interaction of these two loci may affect SLE susceptibility.