Clinical utility of repeat fetal echocardiography in congenital heart disease

OBJECTIVES

To investigate the utility of repeat fetal echocardiography (FE) following a diagnosis of structural congenital heart disease (CHD) on the initial FE. We evaluated how often changes in management and counseling occurred based on subsequent FE findings and sought to determine which types of CHD were more likely to have changes in management and/or counseling based on repeat FE.

METHODS

This was a retrospective review of all patients who presented to our center between January 2012 and January 2019 and who had more than one FE performed for structural CHD. We reviewed consultation notes to determine whether management or counseling had changed based on FE findings at follow-up visits. Management variables included a change in location or mode of delivery, plan for atrial septostomy, initiation of prostaglandin infusion, umbilical line placement and planned admission location (nursery vs neonatal intensive care unit). We defined a counseling change as any of the above changes in management as well as any meaningful refinements in the cardiac diagnosis that led to a change in the overall prognosis or future management. Initial diagnoses were grouped into anatomically/hemodynamically relevant subgroups. Fisher's exact test was used to assess the relationship between the initial diagnosis and changes in management. Post-hoc pairwise comparisons were performed using Dunnett's test.

RESULTS

Between January 2012 and January 2019, 267 patients underwent 534 follow-up FE assessments performed for structural CHD. Management change based on repeat FE occurred in 41/267 (15.4%) cases. A change in management was associated with the diagnosis made at the initial visit (P < 0.001). The proportion of cases with a management change was highest among those with an initial diagnosis of pulmonary valve abnormality/non-critical pulmonary stenosis (4/11 (36.4%)), followed by balanced atrioventricular canal (AVC) defect (5/17 (29.4%)) and left ventricular outflow tract obstruction/aortic valve abnormality or coarctation/interrupted aortic arch (19/68 (27.9%)). No management change occurred in fetuses diagnosed with isolated ventricular septal defect (VSD), truncus arteriosus, pulmonary vein anomaly or isolated arch sidedness/branching abnormality. Compared to those with a VSD, management was significantly more likely to be changed in fetuses with a balanced AVC defect (P = 0.025) and left heart lesions (P = 0.002). Right heart lesions showed a trend towards an increased incidence of management change (P = 0.05). A counseling change based on repeat FE occurred in 108/267 (40.4%) cases. The proportion of cases with a counseling change was highest among those with an initial diagnosis of pulmonary valve abnormality/non-critical pulmonary stenosis (8/11 (72.7%)) and hypoplastic left heart syndrome/critical aortic stenosis (5/9 (55.6%)).

CONCLUSIONS

The clinical utility of follow-up FE is associated with the type of CHD diagnosed. Follow-up FE led to changes in management in several types of CHD, most commonly in cases with an initial diagnosis of right and left outflow obstructive lesions and balanced AVC defect. When developing programmatic protocols for the frequency of FE assessments, the type of CHD should be a major determinant, but additional studies are required to reach a consensus on how often serial FE should be performed for each type of CHD. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

Filamentous Bacteria Resembling Fungal Hyphae: A Diagnostic Pitfall

Introduction/Objective

When exposed to antibiotics or a host immune response, Gram-negative bacilli grow with inhibited septation producing long continuous cells; a phenomenon known as filamentation.

Methods/Case Report

We present a case of a 68-year-old man with quadriplegia, which was caused by the right vertebral artery dissection and subarachnoid hemorrhage requiring an emergent posterior inferior cerebellar artery direct bypass surgery. Lung lower lobe infiltrates were noted 3 days after the surgery. A bronchial wash culture was negative for growth, and a sputum specimen grew Serratia marcescens. The patient was treated with piperacillin/tazobactam, vancomycin, cefepime, cefazolin. After the surgery, he suddenly developed severe cerebral vasospasm of the posterior circulation with cerebellar strokes requiring emergent posterior fossa decompression. He remained on ventricular drainage by external ventricular drainage. After two days, the patient's cerebrospinal fluid (CSF) was sent for evaluation, on which a high segmented neutrophil count of 35% and Gram-negative filamentous organisms with occasional swellings were noted. Multi-drug resistant Serratia marcescens was isolated from the CSF specimen four days later. Neurosurgical procedures were reported to be highly associated with S. marcescens meningitis. The filamentous organisms noted on Gram-stained direct smear most likely represented Gram-negative S. marcescens with filamentation due to administration of sub-inhibitory concentrations of antibiotics.

Results (if a Case Study enter NA)

NA.

Conclusion

Gram-negative bacilli can develop abnormal morphology including elongation, swelling, and filamentation due to stress or sub-inhibitory antibiotic exposure, and it is important for microbiologists and pathologists to be aware of this phenomenon to avoid misinterpretation that may lead to inappropriate treatment.

POS0514 PREDICTION OF RESPONSE TO METHOTREXATE IN PATIENTS WITH RHEUMATOID ARTHRITIS: A MACHINE LEARNING APPROACH USING CLINICAL TRIAL DATA

Background

Methotrexate (MTX) is the preferred initial disease-modifying drug (DMARD) for rheumatoid arthritis (RA). However, up to 50% of patients respond inadequately to MTX (1). Clinically useful predictors that effectively identify patients with RA who are likely to respond to MTX are lacking. Whether machine learning (ML) can provide robust and clinically useful prediction of response to MTX monotherapy in the first months of treatment in patients with early RA using uniformly collected baseline demographics and clinical data has not been investigated in large patient populations.

Objectives

We aimed to identify clinical predictors of response to MTX as the first DMARD among patients with RA using ML methods.

Methods

Randomized clinical trials (RCT) of patients with RA who were DMARD-naïve and randomized to placebo plus MTX were identified and accessed through the Clinical Study Data Request Consortium and Vivli Center for Global Clinical Research Data. Studies with available Disease Activity Score with 28-joint count and erythrocyte sedimentation rate (DAS28-ESR) at baseline, 12 and 24 weeks were included. Latent class modeling of MTX response was performed. Least absolute shrinkage and selection operator (LASSO) and random forest were used to identify predictors of response.

Results

A total of 775 patients from 4 RCTs were included (mean age 50 years, 80% female). Two distinct classes of patients were identified based on DAS28-ESR change over 24 weeks: “good responders” and “poor responders” to MTX treatment (Figure 1). Baseline DAS28-ESR, anti-citrullinated protein antibody (ACPA) and health assessment questionnaire (HAQ) score were the top predictors of good response to MTX using LASSO (Area Under the Curve [AUC] 0.79) and Random Forest models (AUC 0.68) in the external validation set. DAS28-ESR≤7.4, ACPA positive and HAQ≤2 provided the highest likelihood of response (Table 1). Among patients with 12-week DAS28-ESR>3.2, at least 1 point improvement in DAS28-ESR baseline-to-12-week was predictive of achieving DAS28-ESR≤3.2 at 24 weeks.

Table 1.

Matrix prediction model: Probability of achieving a good response to methotrexate at 24 weeks

DAS28ESR≤7.480.1 (76.4, 83.8)77.3 (70.6, 84)PositiveACPA Status77.1 (68.6, 85.6)74.1 (63.3, 84.9)Negative>7.440.3 (32.1, 48.5)36.5 (29.3, 43.6)Positive36.2 (23.3, 49.1)32.5 (20.9, 44.1)Negative≤2>2HAQ

Footnote: The number in each cell represents the percentage and 95% CI of achieving the outcome, based on the combination of predictors at baseline. DAS28-ESR: Disease Activity Score with 28-joint count with erythrocyte sedimentation rate; HAQ: Health assessment questionnaire score; ACPA: Anti-citrullinated protein antibody.

Figure 1.

Two patient class trajectories identified with latent class modeling of DAS28-ESR (N=775)

Conclusion

We have developed and externally validated a prediction model for response to MTX within 24 weeks in DMARD-naïve patients with RA, providing variably weighted clinical features and defined cut-offs for clinical decision-making. Trajectory of DAS28-ESR change over 24 weeks in patients with moderate-to-high RA disease activity at baseline who are starting MTX can be predicted by baseline DAS28-ESR, ACPA status and HAQ-score. Patients with at least 1 unit decline in DAS28-ESR within the first 12 weeks of treatment who have not achieved low disease activity by week 12, may be more likely to achieve low disease activity at 24 weeks. These parameters should be considered as part of the clinical decision-making process when initiating MTX in DMARD-naïve patients with RA.

References

[1]Aletaha D, Smolen JS. Effectiveness profiles and dose dependent retention of traditional disease modifying antirheumatic drugs for rheumatoid arthritis. An observational study. J Rheumatol. 2002;29(8):1631-8.

Acknowledgements

This abstract is based on research using data from data contributors UCB and Roche that has been made available through Vivli, Inc. Vivli has not contributed to or approved, and is not in any way responsible for, the contents of this publication.

Disclosure of Interests

Stephanie Duong: None declared, Cynthia S. Crowson: None declared, Arjun Athreya: None declared, Elizabeth Atkinson: None declared, John M Davis III Grant/research support from: Pfizer, Kenneth J Warrington Speakers bureau: Chemocentryx, Consultant of: Roche/Genentech, Eric Matteson: None declared, Richard Weinshilboum Shareholder of: OneOme, Liewei Wang Shareholder of: OneOme, Elena Myasoedova: None declared.

POS0311 NEUROIMAGING BIOMARKERS IN INDIVIDUALS WITH AND WITHOUT RHEUMATOID ARTHRITIS: RESULTS FROM THE MAYO CLINIC STUDY OF AGING

Background:

Age-related increase in the burden of systemic inflammation is an established key player and potential treatment target in Alzheimer’s disease (AD) and other age-related dementias. (Dregan, Chowienczyk et al. 2015) Although rheumatoid arthritis (RA) is an autoimmune hyper-inflammatory disease, studies on RA and dementia or vascular neuroimaging biomarkers are lacking.

Objectives:

To examine the associations between RA and dementia/vascular neuroimaging biomarkers in the Mayo Clinic Study of Aging (MCSA).

Methods:

The study consisted of 35 RA cases in MCSA and 104 MCSA participants without RA matched 1:3 for age, sex, education, cognitive status (≥50 years old) at baseline and the availability of at least one magnetic resonance imaging (MRI). The primary outcome measures were well established dementia-related neuroimaging biomarkers, including global beta-amyloid (Aβ) using PiB-positron-emission tomography (PET; n=47); neurodegeneration (hypometabolism via FDG-PET (n=45), hippocampal volume (n=139), and cortical thickness via structural MRI [n=138], and cerebrovascular pathology via FLAIR-MRI (white matter hyperintensity [WMH; n=49] burden, subcortical, and cortical infarctions (n=55)). Elevated 11C-PiB-PET was defined as standardized uptake value ratio ≥1.48 in an Alzheimer’s disease (AD)-related region of interest and reduced AD signature cortical thickness as ≤2.68mm (neurodegeneration; N+). Kruskal-Wallis rank sum and Pearson’s chi-squared tests were used to compare the neuroimaging measures between participants with and without RA.

Results:

Participants with vs. without-RA did not differ in age, sex, years of education, major comorbidities, Aβ burden, hippocampal volume, and neurodegeneration measures (Table 1). Although the sample size was small, we observed that RA participants (vs. without-RA) had greater mean WMH volume (relative to the total intracranial volume (TIV) (mean (SD) %: 1.12 (0.57) % vs 0.76 (0.69) % of TIV, p=0.011), were more likely to have cortical infarctions (4 vs.1; p=0.013) and had a higher mean number of cortical infarctions (mean (SD): 0.24 (0.44) vs. 0.05 (0.32), p=0.017).

Table 1.

Participants’ baseline characteristics.

With RAWithout RATotalp value*Age, mean (SD)76.3 (7.9)75.9 (7.9)1390.82Male13 (37%)37 (36%)1390.87Education (years), mean (SD)14.5 (2.5)14.3 (2.4)1390.75Apolipoprotein E ε4 carrier6 (17%)28 (27%)1390.24Cognitively unimpaired27 (77%)83 (80%)1100.94Mild cognitive impairment7 (20%)18 (17%)25Dementia1 (3%)3 (3%)4Reduced AD signature cortical thickness20 (57%)60 (58%)1380.91Elevated β-amyloid4 (33%)11 (31%)470.90FDG PET SUVR1.52 (0.16)1.59 (0.18)450.46White matter hyperintensity volume % of TIV1.12 (0.57)0.76 (0.69)490.011With cortical infarctions4 (24%)1 (3%)550.013

N (%) unless otherwise stated; * Kruskal-Wallis rank sum or Pearson’s Chi-squared test.

SD=standard deviation; AD= Alzheimer’s disease; SUVR=standardized uptake value ratio; TIV= Total intracranial volume.

Conclusion:

Our preliminary data suggest significant differences in cerebrovascular biomarker measures by RA status. Further studies would add valuable information to our understanding and insight into the development of interventions for the prevention of cerebrovascular pathology in RA patients.

References:

[1]Dregan, A., P. Chowienczyk and M. C. Gulliford (2015). “Are Inflammation and Related Therapy Associated with All-Cause Dementia in a Primary Care Population?” J Alzheimers Dis 46(4): 1039-1047.

Acknowledgements:

The study was supported by the NIH AG068192. The Mayo Clinic Study of Aging was supported by the NIH (U01 AG006786, P50 AG016574, R01AG057708, R01 AG011378, R01 AG021927, R01 AG041851, R01 NS097495), the Alexander Family Alzheimer’s Disease Research Professorship of the Mayo Clinic, Mayo Foundation for Medical Education and Research, the Liston Award, the Schuler Foundation and was made possible by the Rochester Epidemiology Project (R01 AG034676).

Disclosure of Interests:

Maria Vassilaki Shareholder of: M. Vassilaki has equity ownership in Abbott Laboratories, Johnson and Johnson, Medronic and Amgen., Grant/research support from: M. Vassilaki has received research funding from Roche and Biogen in the past., Cynthia S. Crowson: None declared, John M Davis III Grant/research support from: JM. Davis III receives research funding from Pfizer., Stephanie Duong: None declared, David Jones: None declared, Michelle Mielke Consultant of: M. Mielke has consulted for Biogen and Brain Protection Company, Prashanthi Vemuri: None declared, Elena Myasoedova: None declared

POS1338 INCIDENCE, PREVALENCE, AND MORTALITY OF CHRONIC PERIAORTITIS: A POPULATION-BASED STUDY

Background:

Chronic periaortitis is an inflammatory condition that typically involves the infrarenal portion of the abdominal aorta. Few studies are available to outline the epidemiology of this rare condition. To date, no epidemiologic studies on periaoritis have been performed in North America.

Objectives:

To evaluate the epidemiology, presentation and outcomes of patients with chronic periaortitis from 1998 through 2018.

Methods:

An inception cohort of patients with incident chronic periaortitis from January 1, 1998 through December 31, 2018, in Olmsted County, Minnesota, USA, was identified based on comprehensive individual medical record review utilizing the Rochester Epidemiology Project medical record linkage system. Inclusion required radiographic and/or histologic confirmation of periarterial soft tissue thickening around at least part of the infra-renal abdominal aorta or the common iliac arteries. Data were collected on demographic characteristics, clinical presentation, renal and radiographic outcomes, and mortality. Incidence rates were age and sex adjusted to the 2010 United States white population.

Results:

Eleven incident cases of chronic periaortitis were identified during the study period. Mean±SD age at diagnosis was 61.8±13.4 years. The cohort included 9 men (82%) and 2 women (18%). The most common presenting symptom was pain with 55% (6/11) reporting abdominopelvic-pelvic pain, 36% (4/11) back pain, and 18% (2/11) flank pain. Obstructive uropathy was present in 73% (8/11) subjects: 3 (27%) unilateral left, 1 (9%) unilateral right, and 4 (36%) bilateral. Mean creatinine at presentation was 2.7±3.4 mg/dL. Ureteral stenting was required at diagnosis in seven patients: unilateral left in 2, unilateral right in 1 and bilateral in 4. All 11 patients received glucocorticoids with a median (IQR) dose of 40 (30, 60) mg/day. Additional non-glucocorticoid therapeutics were used in 10 patients.

Renal function stage at last follow up declined in 2 patients, remained the same in 3 patients and improved in 6 patients. Mean creatinine at last follow-up was 1.2±0.2 mg/dL. Among the seven patients requiring baseline indwelling ureteral stent placement only two required ongoing ureteral stenting at last follow up. None of the four patients without ureteral stenting at diagnosis progressed to require stenting during the follow-up period. No patient underwent ureterolysis surgery in this cohort. Periarterial soft tissue thickening at last follow up had increased in thickness in 1 (9%), was unchanged in 2 (18%), decreased in size but did not resolve in 6 (55%), and fully resolved in 18%.

Age- and sex-adjusted incidence rates per 100,000 population were 0.26 for females, 1.56 for males and 0.87 overall. Overall prevalence on January 1, 2015 was 8.98 per 100,000 population. Median (IQR) length of follow-up was 10.1 (2.5, 13.8) years. Overall mortality was similar to the expected age, sex, and calendar estimates of the Minnesota population with standardized mortality ratio (95% CI) for the entire cohort 2.07 (0.67, 4.84).

Conclusion:

This study reports the first epidemiologic data on chronic periaortitis in the United States. In this cohort of patients with chronic periaortitis, men were approximately 4 times more commonly affected than women. Mortality was not increased compared to the general population.

Disclosure of Interests:

None declared

Exophiala Dermatitidis Isolated From Blood In Patient With Steroid Use

Casestudy

Exophiala dermatitidis is a dematiaceous mold that is associated with subcutaneous, central nervous system and pulmonary infections; osteomyelitis; and disseminated disease. Isolation of E. dermatitidis from patients with mild symptoms may be difficult to interpret whether is a contaminant or asymptomatic patient with serious infection. However, it is important to diagnose asymptomatic patients early in the stage because of up to 25% mortality rate.

Results

77-year-old male with history of chronic obstructive pulmonary disease presented to his pulmonologist with cough. He was started on azithromycin and steroids. His cough worsened and he was transitioned to levofloxacin with continuation of steroid treatment. In addition, he developed fatigue, weakness, poor appetite, chills and nights sweat along with some urinary complaints. His chest X-ray showed infiltrates and he was diagnosed with left lower lung pneumonia and urinary tract infection and was treated with doxycycline and ciprofloxacin. Blood cultures were drawn. Additional past medical history was not significant.

Blood culture became positive on day 4 of incubation. Gram stain showed yeast-like cells, but the blood culture multiplex PCR was negative. Serum cryptococcus antigen was negative. Three days later, a dark shiny olive-colored colony with dark obverse side was isolated. It grew at 42 C. Microscopic examination revealed hyaline and pigmented hyphae with brown conidia. It was identified as Exophiala dermatitidis and confirmed by the state public health laboratory. Blood cultures drawn after hospital admission remained negative. Patient’s symptoms improved with antibiotic treatment. Therefore the clinicians believed that the E. dermatitidis was a probable contaminant and patient was discharged with follow-up. During the follow-up process he developed respiratory infection with Coronavirus (HKU1, NL63, 229E, OC43). Follow-up continues.

Conclusion

Blood cultures are not sensitive for mold infection especially for an uncommon contaminant like E. dermatitidis, it may be difficult to decide whether a positive culture is a real result or not. Fungal antigen tests such as beta-D-glucan test may be helpful in distinguishing between invasive infection and contaminant. Additionally, we believe that in our case, steroid use could have caused a temporary immunosuppression and led to Exophiala dermatitidis infection.

Modification of the sterol profile in milk through feeding

The fortification of milk with phytosterols is an increasingly common practice to enhance the sterol profile and offer consumers potential health benefits. This study investigated whether cattle feed can influence the profile of phytosterols and cholesterol in the milk produced as an alternative to direct fortification of milk. Five experiments were performed using feeds commonly used by Australian dairy farmers and selected formulated rumen-protected feeds. Statistical significances were observed for some individual plant sterols and cholesterol in milk under these differing feeding regimens compared with the respective controls. In the case of the phytosterols, where the daily recommended consumption is typically 2 g per day, the total phytosterols were <0.12 mg/100 mL of milk. An experiment using a rumen-protected feed with high phytosterol levels suggested a decreased transfer of cholesterol to the milk by as much as 20%, although further work is required to confirm these preliminary results. Overall, the study suggests that different feeding practices have minimal effect on the resulting sterol profile of the milk.

Abstract GS5-05: Primary endocrine therapy for ER-positive ductal carcinoma in situ (DCIS) CALGB 40903 (Alliance)

Background: Standard treatment for ductal carcinoma in situ (DCIS) consists of surgery, often followed by adjuvant radiation therapy or endocrine therapy. This current approach is thought to represent overtreatment for some patients. This study was undertaken to determine whether an alternate approach of primary endocrine therapy alone could result in measurable radiographic changes in unresected estrogen receptor (ER)-positive DCIS.

Methods: A phase II open-label single arm multi-center cooperative group trial (CALGB 40903) was conducted for postmenopausal patients diagnosed with ER-positive DCIS. All eligible patients underwent baseline mammography and MRI, followed by 6 months of preoperative therapy with letrozole. Follow up breast MRI was obtained at 3 and 6 months of treatment. The primary endpoint was change in total MRI volume of DCIS enhancement from baseline to 3 months and from baseline to 6 months. Secondary endpoints were change in MRI maximum diameter over baseline and change in mammographic extent of disease over baseline. Endpoints were analyzed via 2-sided paired t-tests (a=0.05).

Results: From 8/1/12 to 2/1/16 108 patients were enrolled; Of the 77 patients who completed letrozole treatment per protocol, 66 patients were assessable. 2 additional patients who did not complete treatment per protocol were considered assessable and thus included in the analysis for a total of 68 patients. Median age of the cohort was 62.7 years. DCIS nuclear grade was low in 10% of patients, intermediate in 49%, and high in 40%. 82% of patients had ER-positive, PR-positive DCIS. The total mean MRI volume decreased from baseline to 3 months by 1.93 cm3 (p&lt;0.001) and from baseline to 6 months by 1.82 cm3 (p&lt;0.001). There was no significant difference in tumor volume between 3 and 6 months. Mean total mammographic tumor diameter decreased from baseline to 6 months by 3.31 mm2 (p=0.078).

Conclusions: In a cohort of postmenopausal women treated with 6 months of preoperative endocrine therapy for ER-positive DCIS, MRI volume decreased markedly by 3 months, while mammographic extent of disease was not altered significantly. Correlation of imaging changes with pathology and baseline biomarkers will be conducted. These results will help determine whether MRI could be an effective modality for monitoring treatment response in some patients treated with primary endocrine therapy for ER-positive DCIS.

Citation Format: Hwang ES, Duong S, Bedrosian I, Allred J, Wisner D, Hyslop T, Caudle A, Guenther J, Hudis C, Winer E, Esserman L, Hylton N. Primary endocrine therapy for ER-positive ductal carcinoma in situ (DCIS) CALGB 40903 (Alliance) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr GS5-05.

Rapid measurement of phytosterols in fortified food using gas chromatography with flame ionization detection

A novel method for the measurement of total phytosterols in fortified food was developed and tested using gas chromatography with flame ionization detection. Unlike existing methods, this technique is capable of simultaneously extracting sterols during saponification thus significantly reducing extraction time and cost. The rapid method is suitable for sterol determination in a range of complex fortified foods including milk, cheese, fat spreads, oils and meat. The main enhancements of this new method include accuracy and precision, robustness, cost effectiveness and labour/time efficiencies. To achieve these advantages, quantification and the critical aspects of saponification were investigated and optimised. The final method demonstrated spiked recoveries in multiple matrices at 85-110% with a relative standard deviation of 1.9% and measurement uncertainty value of 10%.

Genetic diversity and molecular identification of mosquito species in the Anopheles maculatus group using the ITS2 region of rDNA

The species diversity and genetic structure of mosquitoes belonging to the Anopheles maculatus group in Southeast Asia were investigated using the internal transcribed spacer 2 (ITS2) of ribosomal DNA (rDNA). A molecular phylogeny indicates the presence of at least one hitherto unrecognised species. Mosquitoes of chromosomal form K from eastern Thailand have a unique ITS2 sequence that is 3.7% divergent from the next most closely related taxon (An. sawadwongporni) in the group. In the context of negligible intraspecific variation at ITS2, this suggests that chromosomal form K is most probably a distinct species. Although An. maculatus sensu stricto from northern Thailand and southern Thailand/peninsular Malaysia differ from each other in chromosomal banding pattern and vectorial capacity, no intraspecific variation was observed in the ITS2 sequences of this species over this entire geographic area despite an extensive survey. A PCR-based identification method was developed to distinguish five species of the group (An. maculatus, An. dravidicus, An. pseudowillmori, An. sawadwongporni and chromosomal form K) to assist field-based studies in northwestern Thailand. Sequences from 187 mosquitoes (mostly An. maculatus and An. sawadwongporni) revealed no intraspecific variation in specimens from Thailand, Cambodia, mainland China, Malaysia, Taiwan and Vietnam, suggesting that this identification method will be widely applicable in Southeast Asia. The lack of detectable genetic structure also suggests that populations of these species are either connected by gene flow and/or share a recent common history.

A common breakpoint on 11q23 in carriers of the constitutional t(11;22) translocation

Structural chromosomal rearrangements occur commonly in the general population. Individuals that carry a balanced translocation are at risk of having unbalanced offspring; therefore, the frequency of translocations in couples with recurrent spontaneous abortions is higher than that in the general population. The constitutional t(11;22) translocation is the most common recurrent non-Robertsonian translocation in humans and may serve as a model to determine the mechanism that causes recurrent meiotic translocations. We previously localized the t(11;22) translocation breakpoint to a region on 22q11 within a low-copy repeat, termed "LCR22." To define the breakpoint on 11q23 and to ascertain whether this region shares homology with LCR22 sequences, we performed haplotype analysis on patients with der(22) syndrome. We found that the breakpoint on 11q23 occurred between two genetic markers, D11S1340 and APOC3-tetra, both being present within a single bacterial-artificial-chromosome clone. To determine whether the breakpoint occurred within the same region among a larger set of carriers, we performed FISH mapping studies. The breakpoints were all within the same clone, suggesting that this region may harbor sequences that are prone to breakage. We narrowed the breakpoint interval, in both derivative chromosomes from two unrelated carriers, to a 190-bp, AT-rich repeat, which indicates that this repeat may mediate recombination events on chromosome 11. Interestingly, the LCR22s harbor AT-rich repeats, suggesting that this sequence motif may mediate recombination events in nonhomologous chromosomes during meiosis.