Arteriovenous Fistula Histology, Hemodynamics, and Wall Mechanics: A Case Report of Successful and Failed Access in a Single Patient

The low 1-year patency rate of mature arteriovenous fistulas (AVFs) remains a significant clinical problem. Although vessel properties and biomechanics have been suggested to affect AVF function, understanding their roles in AVF patency failure is challenging owing to the heterogeneity within the patient population, including demographics and comorbid conditions. In this study, we present a case of a patient with 2 upper-arm AVFs with different 1-year patency outcomes and investigate whether they had different histologic features before the AVF creation surgery and biomechanics at 1 day and 6 weeks after the AVF creation surgery using magnetic resonance imaging-based fluid structure interaction simulations. Despite both AVFs being in the upper arm, created <1 year apart by the same surgeon, and having similar preoperative vessel diameters, the 1-year patent AVF had less preoperative intimal collagen and higher wall shear stress 1 day after AVF creation, when compared with the AVF that failed by 1 year. Thus, a low intimal collagen content before the AVF surgery and higher wall shear stress immediately after the AVF creation surgery may be important for long-term AVF patency and should be investigated with larger cohorts.

Effects of endothelial nitric oxide synthase on mouse arteriovenous fistula hemodynamics

Newly created arteriovenous fistulas (AVFs) often fail to mature for dialysis use due to disturbed blood flow at and near the AVF anastomosis. The disturbed flow inhibits the endothelial nitric oxide synthase (NOS3) pathway, thus decreasing the production of nitric oxide, a vasodilator. Previously, our group reported that NOS3 expression levels affect AVF lumen size in a mouse model. In this study, we performed MRI-based computational fluid dynamics simulations to investigate the hemodynamical parameters (velocity, wall shear stress (WSS), and vorticity) in a mouse AVF model at day 7 and day 21 post-AVF creation using three NOS3 strains: overexpression (OE), knockout (KO), and wild-type (WT) control. This study is the first to reveal hemodynamics over time in mouse AVFs, consider spatial heterogeneity along the vein, and reveal the effect of NOS3 on the natural history of mouse AVF hemodynamics. From day 7 to day 21, OE has smoother streamlines and had significantly lower vorticity and WSS than WT and KO, suggesting that WSS was attempting to return to pre-surgery baseline, respectively. Our results conclude that the overexpression of NOS3 leads to desired optimal hemodynamics during AVF remodeling. Future studies can investigate enhancing the NOS3 pathway to improve AVF development.

Differential hemodynamics between arteriovenous fistulas with or without intervention before successful use

A significant number of arteriovenous fistulas (AVFs) fail to maturate for dialysis. Although interventions promote maturation, functional primary patency loss is higher for AVFs with interventions (assisted maturation) than AVFs without interventions (un-assisted maturation). Although blood flow-associated hemodynamics have long been proposed to affect AVF remodeling, the optimal hemodynamic parameters for un-assisted maturation are unclear. Additionally, AVF maturation progress is generally not investigated until 6 weeks after AVF creation, and the examination is focused on the AVF's venous limb. In this exploratory study, patients (n = 6) underwent magnetic resonance imaging (MRI) at 1 day, 6 weeks, and 6 months after AVF creation surgery. Before successful use for hemodialysis, three AVFs required intervention and three did not. MRI of the AVFs were used to calculate lumen cross-sectional area (CSA) and perform computational fluid dynamics (CFD) to analyze hemodynamics, including velocity, wall shear stress (WSS), and vorticity. For the venous limb, the no-intervention group and intervention group had similar pre-surgery vein diameter and 1-day post-surgery venous CSA. However, the no-intervention group had statistically larger 1-day venous velocity (0.97 ± 0.67 m/s; mean ± SD), WSS (333 ± 336 dyne/cm2) and vorticity (1709 ± 1290 1/s) than the intervention group (velocity = 0.23 ± 0.10 m/s; WSS = 49 ± 40 dyne/cm2; vorticity = 493.1 ± 227 1/s) (P < 0.05). At 6 months, the no-intervention group had statistically larger venous CSA (43.5 ± 27.4 mm2) than the intervention group (15.1 ± 6.2 mm2) (P < 0.05). Regarding the arterial limb, no-intervention AVF arteries also had statistically larger 1-day velocity (1.17 ± 1.0 m/s), WSS (340 ± 423 dyne/cm2), vorticity (1787 ± 1694 1/s), and 6-month CSA (22.6 ± 22.7 mm2) than the intervention group (velocity = 0.64 ± 0.36 m/s; WSS = 104 ± 116 dyne/cm2, P < 0.05; vorticity = 867 ± 4551/s; CSA = 10.7 ± 6.0 mm2, P < 0.05). Larger venous velocity, WSS, and vorticity immediately after AVF creation surgery may be important for later lumen enlargement and AVF maturation, with the potential to be used as a tool to help diagnose poor AVF maturation earlier. However, future studies using a larger cohort are needed to validate this finding and determine cut off values, if any.

Medical Image-Based Computational Fluid Dynamics and Fluid-Structure Interaction Analysis in Vascular Diseases

Hemodynamic factors, induced by pulsatile blood flow, play a crucial role in vascular health and diseases, such as the initiation and progression of atherosclerosis. Computational fluid dynamics, finite element analysis, and fluid-structure interaction simulations have been widely used to quantify detailed hemodynamic forces based on vascular images commonly obtained from computed tomography angiography, magnetic resonance imaging, ultrasound, and optical coherence tomography. In this review, we focus on methods for obtaining accurate hemodynamic factors that regulate the structure and function of vascular endothelial and smooth muscle cells. We describe the multiple steps and recent advances in a typical patient-specific simulation pipeline, including medical imaging, image processing, spatial discretization to generate computational mesh, setting up boundary conditions and solver parameters, visualization and extraction of hemodynamic factors, and statistical analysis. These steps have not been standardized and thus have unavoidable uncertainties that should be thoroughly evaluated. We also discuss the recent development of combining patient-specific models with machine-learning methods to obtain hemodynamic factors faster and cheaper than conventional methods. These critical advances widen the use of biomechanical simulation tools in the research and potential personalized care of vascular diseases.

Nitric oxide releasing nanomatrix gel treatment inhibits venous intimal hyperplasia and improves vascular remodeling in a rodent arteriovenous fistula

Vascular access is the lifeline for hemodialysis patients and the single most important component of the hemodialysis procedure. Arteriovenous fistula (AVF) is the preferred vascular access for hemodialysis patients, but nearly 60% of AVFs created fail to successfully mature due to early intimal hyperplasia development and poor outward remodeling. There are currently no therapies available to prevent AVF maturation failure. First, we showed the important regulatory role of nitric oxide (NO) on AVF development by demonstrating that intimal hyperplasia development was reduced in an overexpressed endothelial nitric oxide synthase (NOS3) mouse AVF model. This supported the rationale for the potential application of NO to the AVF. Thus, we developed a self-assembled NO releasing nanomatrix gel and applied it perivascularly at the arteriovenous anastomosis immediately following rat AVF creation to investigate its therapeutic effect on AVF development. We demonstrated that the NO releasing nanomatrix gel inhibited intimal hyperplasia formation (more than 70% reduction), as well as improved vascular outward remodeling (increased vein diameter) and hemodynamic adaptation (lower wall shear stress approaching the preoperative level and less vorticity). Therefore, direct application of the NO releasing nanomatrix gel to the AVF anastomosis immediately following AVF creation may enhance AVF development, thereby providing long-term and durable vascular access for hemodialysis.

Analysis of Geometric and Hemodynamic Profiles in Rat Arteriovenous Fistula Following PDE5A Inhibition

Arteriovenous fistula (AVF) is essential for chronic kidney disease (CKD) patients on hemodialysis, but treatment for AVF maturation failure remains an unmet clinical need. Successful AVF remodeling occurs through sufficient lumen expansion to increase AVF blood flow and lumen area. Aberrant blood flow is thought to impair AVF remodeling, but previous literature has largely focused on hemodynamics averaged over the entire AVF or at a single location. We hypothesized that hemodynamics is heterogeneous, and thus any treatment's effect size is heterogeneous in the AVF. To test our hypothesis, we used the PDE5A inhibitor sildenafil to treat AVFs in a rat model and performed magnetic resonance imaging (MRI) based computational fluid dynamics (CFD) to generate a detailed spatial profile of hemodynamics in AVFs. 90 mg/kg of sildenafil was administered to rats in their drinking water for 14 days. On day 14 femoral AVFs were created in rats and sildenafil treatment continued for another 21 days. 21 days post-AVF creation, rats underwent non-contrast MRI for CFD and geometrical analysis. Lumen cross-sectional area (CSA) and flow rate were used to quantify AVF remodeling. Parameters used to describe aberrant blood flow include velocity magnitude, wall shear stress (WSS), oscillatory shear index (OSI), and vorticity. Geometrical parameters include arterial-venous (A-V) distance, anastomosis angle, tortuosity, and nonplanarity angle magnitude. When averaged across the entire AVF, sildenafil treated rats had significantly higher CSA, flow rate, velocity, WSS, OSI, and vorticity than control rats. To analyze heterogeneity, the vein was separated into zones: 0-5, 5-10, 10-15, and 15-20 mm from the anastomosis. In both groups: 1) CSA increased from the 0-5 to 15-20 zone; 2) velocity, WSS, and vorticity were highest in the 0-5 zone and dropped significantly thereafter; and 3) OSI increased at the 5-10 zone and then decreased gradually. Thus, the effect size of sildenafil on AVF remodeling and the relationship between hemodynamics and AVF remodeling depend on location. There was no significant difference between control and sildenafil groups for the other geometric parameters. Rats tolerated sildenafil treatment well, and our results suggest that sildenafil may be a safe and effective therapy for AVF maturation.

Human myelomeningocele risk and ultra-rare deleterious variants in genes associated with cilium, WNT-signaling, ECM, cytoskeleton and cell migration

Myelomeningocele (MMC) affects one in 1000 newborns annually worldwide and each surviving child faces tremendous lifetime medical and caregiving burdens. Both genetic and environmental factors contribute to disease risk but the mechanism is unclear. This study examined 506 MMC subjects for ultra-rare deleterious variants (URDVs, absent in gnomAD v2.1.1 controls that have Combined Annotation Dependent Depletion score ≥ 20) in candidate genes either known to cause abnormal neural tube closure in animals or previously associated with human MMC in the current study cohort. Approximately 70% of the study subjects carried one to nine URDVs among 302 candidate genes. Half of the study subjects carried heterozygous URDVs in multiple genes involved in the structure and/or function of cilium, cytoskeleton, extracellular matrix, WNT signaling, and/or cell migration. Another 20% of the study subjects carried heterozygous URDVs in candidate genes associated with gene transcription regulation, folate metabolism, or glucose metabolism. Presence of URDVs in the candidate genes involving these biological function groups may elevate the risk of developing myelomeningocele in the study cohort.

Analyses of hemodialysis arteriovenous fistula geometric configuration and its associations with maturation and reintervention

OBJECTIVE

An arteriovenous fistula (AVF) is the preferred vascular access for chronic hemodialysis; however, the rates of AVF maturation failure and reintervention remain high. We investigated the AVF geometric parameters and their associations with AVF physiologic maturation and reintervention in a prospective multicenter study.

METHODS

From 2011 to 2016, patients undergoing vein end-to-artery side upper extremity AVF creation surgery were recruited. Contrast-free dark blood and phase-contrast magnetic resonance imaging (MRI) scans were performed using 3.0T scanners to obtain the AVF lumen geometry and flow rates, respectively, at postoperative day 1, week 6, and month 6. The arteriovenous anastomosis angle, nonplanarity, and tortuosity of the fistula were calculated according to the lumen centerlines. AVFs were considered physiologically matured if, using the week 6 MRI data, the flow rate was ≥500 mL/min and the minimum vein lumen diameter was ≥5 mm. The associations of these geometric parameters with AVF maturation and reintervention due to perianastomotic and mid-vein stenosis within 1 year were assessed.

RESULTS

A total of 111 patients had a usable day 1 MRI scan, with most having upper arm AVFs (n = 73). Compared with the forearm AVFs, upper arm AVFs had greater anastomosis angles (P < .001), larger deviations from a plane (nonplanarity; P = .002), and more prominent tortuosity (P = .038) at day 1. These parameters significantly increased between day 1 and week 6 in upper arm AVFs. In contrast, significant changes in these parameters in forearm AVFs were not observed. The rate of maturation was 54% and 86% for forearm and upper arm AVFs, respectively. None of the geometric parameters at day 1 were associated with AVF maturation in either location. The rate of reintervention was 24% and 30% for forearm and upper arm AVFs, respectively, with a larger nonplanarity angle at day 1 associated with less reintervention (30° ± 15° vs 21° ± 10°; P = .034) in upper arm AVFs only. This relationship was unchanged after adjusting for age, sex, race, dialysis status, or diabetes.

CONCLUSIONS

In our study, upper arm fistulas had a larger anastomosis angle, were more nonplanar, and had more tortuous veins than forearm fistulas. For upper arm fistulas, a larger nonplanarity angle is associated with a lower rate of reintervention within 1 year. Once confirmed, vascular surgeons could consider increasing the nonplanarity angle by incorporating a tension-free gentle curvature in the proximal segment of the mobilized vein to reduce reinterventions when creating an upper arm fistula.

The geometry of arteriovenous fistulas using endothelial nitric oxide synthase mouse models

BACKGROUND

Arteriovenous fistula (AVF) maturation failure is a significant clinical problem in the hemodialysis population. Geometric parameters of human AVFs were associated with AVF development, but causative studies are lacking. We characterized mouse AVF geometry using endothelial nitric oxide synthase (NOS3) mouse models.

METHODS

Carotid-jugular AVFs were created in NOS3 overexpression (OE), knockout (KO), and wild type (WT) mice. At 7 and 21 days postcreation, black-blood magnetic resonance images of AVFs were acquired and used to build three-dimensional reconstructions of AVF lumens. We used these reconstructions to calculate the lumen area, lumen centerline, and centerline-derived parameters: anastomosis angle, tortuosity, nonplanarity angle, and location of maximal distance between the feeding artery and AVF vein. Inter- and intrauser variabilities were also determined.

RESULTS

When all mice were considered, increased minimum AVF venous lumen area was accompanied by increased venous tortuosity and increased distance between the artery and vein, with both remaining in-plane with the anastomosis. At day 7, the lumen area of AVFs from all strains was 1.5- to 2.5-fold larger than native veins. Furthermore, at day 21, AVF lumen in NOS3 OE (4.04±1.43 mm2) was significantly larger than KO (2.74±1.34 mm2) (P<0.001) and WT (2.94±1.30 mm2) mice (p<0.001). At day 21, the location of maximal artery-vein distance on the vein was further away from the anastomosis in OE (4.49±0.66 mm) than KO (2.87±0.38 mm) (p=0.001). Other geometric parameters were not significantly different between mouse strains or time points. Inter- and intrauser variabilities were small, indicating the reliability and reproducibility of our protocol.

CONCLUSIONS

Our study presents a detailed characterization of mouse AVF geometry, and a robust protocol for future mechanistic studies to investigate the role of molecular pathways in AVF geometry. Identifying a geometry related to desired AVF remodeling can help inform surgery to enhance AVF maturation.

Silica Nanoparticle-Endothelial Interaction: Uptake and Effect on Platelet Adhesion under Flow Conditions

Silica nanoparticles are extensively used in biomedical applications and consumer products. Little is known about the interaction of these NPs with the endothelium and effect on platelet adhesion under flow conditions in circulation. In this study, we investigated the effect of silica nanoparticles on the endothelium and its inflammation, and subsequent adhesion of flowing platelets in vitro. Platelet counts adhered onto the surface of endothelial cells in the presence of nanoparticles increased at both low and high concentrations of nanoparticles. Preincubation of endothelial cells with nanoparticles also increased platelet adhesion. Interestingly, platelet adhesion onto TNF-α-treated endothelial cells decreased in the presence of nanoparticles at different concentrations as compared with the absence of nanoparticles. We monitored the expression of different endothelial proteins, known to initiate platelet adhesion, in the presence and absence of silica nanoparticles. We found that silica nanoparticles caused changes in the endothelium such as overexpression of PECAM that promoted platelet adhesion to the endothelial cell.

Finding the genetic mechanisms of folate deficiency and neural tube defects-Leaving no stone unturned

Neural tube defects (NTDs) occur secondary to failed closure of the neural tube between the third and fourth weeks of gestation. The worldwide incidence ranges from 0.3 to 200 per 10,000 births with the United States of American NTD incidence at around 3-6.3 per 10,000 dependent on race and socioeconomic background. Human NTD incidence has fallen by 35-50% in North America due to mandatory folic acid fortification of enriched cereal grain products since 1998. The US Food and Drug Administration has approved the folic acid fortification of corn masa flour with the goal to further reduce the incidence of NTDs, especially among individuals who are Hispanic. However, the genetic mechanisms determining who will benefit most from folate enrichment of the diet remains unclear despite volumes of literature published on studies of association of genes with functions related to folate metabolism and risk of human NTDs. The advances in omics technologies provides hypothesis-free tools to interrogate every single gene within the genome of NTD affected individuals to discover pathogenic variants and methylation targets throughout the affected genome. By identifying genes with expression regulated by presence of folate through transcriptome profiling studies, the genetic mechanisms leading to human NTDs due to folate deficiency may begin to be more efficiently revealed.

Promotor genotype of the platelet-derived growth factor receptor-alpha gene shows population stratification but not association with spina bifida meningomyelocele

Neural tube defects (NTDs) constitute a major group of congenital malformations with an overall incidence of approximately 1-2 in 1,000 live births in the United States. Hispanic Americans have a 2.5 times higher risk than the Caucasian population. Spina bifida meningomyelocele (SBMM) is a major clinical presentation of NTDs resulting from lack of closure of the spinal cord caudal to the head. In a previous study of spina bifida (SB) patients of European Caucasian descent, it was suggested that specific haplotypes of the platelet-derived growth factor receptor-alpha (PDGFRA) gene P1 promoter strongly affected the rate of NTD genesis. In our study, we evaluated the association of PDGFRA P1 in a group of 407 parent-child triads (167 Caucasian, 240 Hispanics) and 164 unrelated controls (89 Caucasian, 75 Hispanic). To fully evaluate the association of PDGFRA P1, we performed both transmission-disequilibrium test (TDT) and association analyses to test the hypotheses that PDGFRA P1 was (1) transmitted preferentially in SBMM affected children and (2) associated with the condition of SBMM comparing affected children to unaffected controls. We did find that there was a different allelic and genotypic distribution of PDGFRA P1 when comparing Hispanics and Caucasians. However, neither ethnic group showed strong association between SBMM and the PDGFRA P1 region. These findings suggest that PDGFRA P1 does not have a major role in the development of SBMM.

Benign multicystic peritoneal mesothelioma: cases reports in the family with diverticulosis and literature review

We report on benign multicystic peritoneal mesothelioma in two siblings whose family had a history of multiple familial diseases including diverticulosis. After a genetic evaluation and a chromosomal analysis, we were not able to identify a specific genetic cause of the family's pattern of disease. We assumed that previous surgical procedures and the chronic inflammatory process from diverticulitis were the underlying etiology. Both patients had multiple recurrences with indolent courses similar to those reported in other cases. After the recurrences, one patient was treated with cystic aspiration and the other with hormones. The cysts in both cases regressed partially but the patients were relieved of their clinical symptoms, for 2 years after cystic drainage in one case and for 5 years after hormonal treatment in the other.

Testing for genetic associations in a spina bifida population: analysis of the HOX gene family and human candidate gene regions implicated by mouse models of neural tube defects

Neural tube defects (NTDs) are among the most common severely disabling birth defects in the United States, affecting approximately 1-2 of every 1,000 live births. The etiology of NTDs is multifactorial, involving the combined action of both genetic and environmental factors. HOX genes play a central role in establishing the initial body plan by providing positional information along the anterior-posterior body and limb axis and have been implicated in neural tube closure. There are many mouse models that exhibit both naturally occurring NTDs in various mouse strains as well as NTDs that have been created by "knocking out" various genes. A nonparametric linkage method, the transmission disequilibrium test (TDT), was utilized to test the HOX gene family and human equivalents of genes (when known) or the syntenic region in humans to those in mouse models which could play a role in the formation of NTDs. DNA from 459 spina bifida (SB) affected individuals and their parents was tested for linkage and association utilizing polymorphic markers from within or very close to the HOXA, HOXB, HOXC, and HOXD genes as well as from within the genes/gene regions of eight mouse models that exhibit NTDs. No significant findings were obtained for the tested markers.

Testing for genetic associations with the PAX gene family in a spina bifida population

Neural tube defects (NTDs) are among the most common severely disabling birth defects in the United States, affecting approximately 1-2 of every 1,000 live births. The etiology of NTDs is multifactorial, involving the combined action of both genetic and environmental factors. A nonparametric linkage method, the transmission disequilibrium test (TDT), was utilized to determine if the genes in the PAX family play a role in the formation of NTDs. DNA from 459 spina bifida (SB) patients and their parents (430 mothers and 239 fathers, for a total population of 1,128 subjects) was tested for linkage and association utilizing polymorphic markers from within or very close to the PAX genes of interest. Significant findings were obtained for the following markers: marker locus D20S101 flanking the PAX1 gene (P = 0.019), marker locus D1S228 within the PAX7 gene (P = 0.011), and marker locus D2S110 within the PAX8 gene (P = 0.013). Even though our findings are only mildly significant, given the known expression patterns of the PAX genes in development and the availability of their sequences, we elected to follow up these results by testing these genes directly for mutations utilizing single-strand conformational analysis (SSCA) and direct sequencing. Multiple variations were detected in each of the PAX genes with significant TDT results; however, these variations were not passed from parent to child in phase with the positively transmitted allele. Therefore, it is unlikely that these variations contribute to susceptibility for SB, but rather are previously unreported polymorphisms.

The generation and characterization of a cell line derived from a sporadic renal angiomyolipoma: use of telomerase to obtain stable populations of cells from benign neoplasms

Angiomyolipomas are benign tumors of the kidney derived from putative perivascular epithelioid cells, that may undergo differentiation into cells with features of melanocytes, smooth muscle, and fat. To gain further insight into angiomyolipomas, we have generated the first human angiomyolipoma cell line by sequential introduction of SV40 large T antigen and human telomerase into human angiomyolipoma cells. These cells show phenotypic characteristics of angiomyolipomas, namely differentiation markers of smooth muscle (smooth muscle actin), adipose tissue (peroxisome proliferator-activator receptor gamma, PPARgamma), and melanocytes (microophthalmia, MITF), thus demonstrating that a single cell type can exhibit all of these phenotypes. These cells should serve as a valuable tool to elucidate signal transduction pathways underlying renal angiomyolipomas.

Methylenetetrahydrofolate reductase and spina bifida: evaluation of level of defect and maternal genotypic risk in Hispanics

The C677T and A1298C mutations in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene are each associated with reduced MTHFR activity. The C677T mutation in the heterozygous and homozygous state correlates with increased enzyme thermolability, with homozygous mutant genotypes showing significantly elevated plasma homocysteine levels and decreased plasma folate levels. The A1298C mutation results in decreased MTHFR activity, but changes in neither homocysteine nor folate levels are associated with A1298C variant genotypes. Our study determined the frequencies of the C677T and A1298C MTHFR mutations for spina bifida (SB) cases, mothers and fathers of SB cases, and controls in Hispanics of Mexican-American descent. In addition, our subject population was further categorized as to whether the spina bifida lesion occurred as an upper or lower level defect, according to the Van Allen "multi-site closure" model. Hispanic SB cases with upper level defects and their mothers were homozygous for the C677T variant allele at a higher rate than their respective controls (OR = 1.5 [95% CI 0.8-2.9], P = 0.30; OR = 2.3 [1.1-4.8], P = 0.04, respectively), with statistically significant results seen only for the maternal homozygous genotype. Homozygosity for the A1298C mutation was seen at a higher rate only in Hispanic mothers of both upper and lower level SB cases when compared to controls, but these results were not statistically significant. Our study provides evidence that the maternal C677T MTHFR homozygous mutant genotype is a risk factor for upper level spina bifida defects in Hispanics.

Spina bifida and other neural tube defects

NTDs, resulting from failure of the neural tube to close during the fourth week of embryogenesis, are the most common severely disabling birth defects in the United States, with a frequency of approximately 1 of every 2000 births. Neural tube malformations involving the spinal cord and vertebral arches are referred to as spina bifida, with severe types of spina bifida involving protrusion of the spinal cord and/or meninges through a defect in the vertebral arch. Depending on the level of the lesion, interruption of the spinal cord at the site of the spina bifida defect causes paralysis of the legs, incontinence of urine and feces, anesthesia of the skin, and abnormalities of the hips, knees, and feet. Two additional abnormalities often seen in children with spina bifida include hydrocephalus and the Arnold-Chiari type II malformation. Despite the physical and particular learning disabilities children with spina bifida must cope with, participation in individualized educational programs can allow these children to develop skills necessary for autonomy in adulthood. Advances in research to uncover the molecular basis of NTDs is enhanced by knowledge of the link between both the environmental and genetic factors involved in the etiology of NTDs. The most recent development in NTD research for disease-causing genes is the discovery of a genetic link to the most well-known environmental cause of neural tube malformation, folate deficiency in pregnant women. Nearly a decade ago, periconceptional folic acid supplementation was proven to decrease both the recurrence and occurrence of NTDs. The study of folate and its association with NTDs is an ongoing endeavor that has led to numerous studies of different genes involved in the folate metabolism pathway, including the most commonly studied thermolabile mutation (C677T) in the MTHFR gene. An additional focus for NTD research involves mouse models that exhibit both naturally occurring NTDs, as well as those created by experimental design. We hope the search for genes involved in the risk and/or development of NTDs will lead to the development of strategies for prevention and treatment. The most recent achievement in treatment of NTDs involves the repair of meningomyelocele through advancements in fetal surgery. Convincing experimental evidence exists that in utero repair preserves neurologic function, as well as resolving the hydrocephalus and Arnold-Chiari malformation that often accompany meningomyelocele defects. However, follow-up is needed to completely evaluate long-term neurologic function and overall improved quality of life. And in the words of Olutoye and Adzick, "until the benefits of fetal [meningomyelocele] repair are carefully elucidated, weighed against maternal and fetal risks, and compared to conventional postnatal therapy, this procedure should be restricted to a few centers that are committed (clinically and experimentally) to investigating these issues."

Exon scanning of the entire TSC2 gene for germline mutations in 40 unrelated patients with tuberous sclerosis

Tuberous sclerosis complex (TSC) is a dominantly inherited multisystem disorder resulting in the development of hamartomatous growths in many organs. Genetic heterogeneity has been demonstrated linking the familial cases to either TSC1 at 9q34.3, or TSC2 at 16p13.3. About two-thirds of the TSC cases are sporadic and appear to represent new mutations. While both genes are thought to account for all familial cases, with each representing approximately 50% of the mutations, the proportion of sporadic cases with mutations in TSC1 and TSC2 is yet to be determined. We have examined the entire coding sequence of the TSC2 gene in 20 familial and 20 sporadic cases and identified a total of twenty-one mutations representing 50% and 55% of familial and sporadic cases respectively. Our rate of mutation detection is significantly higher than other published reports. Twenty out of 21 mutations are novel and include 6 missense, 6 nonsense, 5 frameshifts, 2 splice alterations, a 34 bp deletion resulting in abnormal splicing, and an 18 bp deletion which maintains the reading frame. The mutations are distributed throughout the coding sequence with no specific hot spots. There is no apparent correlation between mutation type and clinical severity of the disease. Our results document that at least 50% of sporadic cases arise from mutations in the TSC2 gene. The location of the mutations described here, particularly the missense events, should be valuable for further functional analysis of this tumor suppressor protein.

Mutational analysis of the tuberous sclerosis gene TSC2 in patients with pulmonary lymphangioleiomyomatosis

Pulmonary lymphangioleiomyomatosis (LAM) is a rare disorder limited almost exclusively to women of reproductive age. LAM affects about 5% of women with tuberous sclerosis complex (TSC). LAM also occurs in women who do not have TSC (sporadic LAM). TSC is a tumour suppressor gene syndrome characterised by seizures, mental retardation, and tumours in the brain, heart, and kidney. Angiomyolipomas, which are benign tumours with smooth muscle, fat, and dysplastic vascular components, are the most common renal tumour in TSC. Renal angiomyolipomas also occur in 63% of sporadic LAM patients. We recently found that 54% of these angiomyolipomas have TSC2 loss of heterozygosity, leading to the hypothesis that sporadic LAM is genetically related to TSC. In this study, we screened DNA from 21 women with sporadic LAM for mutations in all 41 exons of TSC2. Twelve of the patients had known renal angiomyolipomas. No TSC2 mutations were detected. We did find three silent TSC2 polymorphisms. We conclude that patients with sporadic LAM, including those with renal angiomyolipomas, do not have a high frequency of germline mutations in the coding region of TSC2.

Tuberous Sclerosis Consensus Conference: recommendations for diagnostic evaluation. National Tuberous Sclerosis Association

At the recent Tuberous Sclerosis Consensus Conference, a subcommittee proposed recommendations to guide the rational use of diagnostic studies in patients with tuberous sclerosis complex. Recommendations were made for diagnostic evaluation at the time of diagnosis, when testing helps both to establish the diagnosis and to identify potential complications. Additional guidelines were proposed for the ongoing surveillance of established patients to detect later complications of tuberous sclerosis complex. In the absence of comprehensive population studies to govern the use of diagnostic studies in individuals with tuberous sclerosis complex, the panel developed guidelines based on the disorder's natural history, concentrating on complications that are common, clinically significant, and more easily managed when found early. Finally, the group made suggestions for the use of diagnostic tests to identify family members who have tuberous sclerosis complex. Although these recommendations should standardize and improve our use of diagnostic studies in individuals with tuberous sclerosis complex, the clinical approach in a given patient must remain flexible enough to meet the needs of individual patients and families.

Germ-line mosaicism in tuberous sclerosis: how common?

Two-thirds of cases of tuberous sclerosis complex (TSC) are sporadic and usually are attributed to new mutations, but unaffected parents sometimes have more than one affected child. We sought to determine how many of these cases represent germ-line mosaicism, as has been reported for other genetic diseases. In our sample of 120 families with TSC, 7 families had two affected children and clinically unaffected parents. These families were tested for mutations in the TSC1 and TSC2 genes, by Southern blotting and by single-strand conformational analysis. Unique variants were detected in six families. Each variant was present and identical in both affected children of a family but was absent in both parents and the unaffected siblings. Sequencing of the variants yielded two frameshift mutations, one missense mutation, and two nonsense mutations in TSC2 and one nonsense mutation in TSC1. To determine which parent contributed the affected gametes, the families were analyzed for linkage to TSC1 and TSC2, by construction of haplotypes with markers flanking the two genes. Linkage analysis and loss-of-heterozygosity studies indicated maternal origin in three families, paternal origin in one family, and either being possible in two families. To evaluate the possibility of low-level somatic mosaicism for TSC, DNA from lymphocytes of members of the six families were tested by allele-specific PCR. In all the families, the mutant allele was detected only in the known affected individuals. We conclude that germ-line mosaicism was present in five families with mutations in the TSC2 gene and in one family with the causative mutation in the TSC1 gene. The results have implications for genetic counseling of families with seemingly sporadic TSC.

Tuberous sclerosis complex consensus conference: revised clinical diagnostic criteria

At the recent tuberous sclerosis complex consensus conference, the clinical diagnostic criteria for tuberous sclerosis complex were simplified and revised to reflect both new clinical information about tuberous sclerosis complex and an improved understanding of the disorder derived from molecular genetic studies. Based on this new information, some clinical signs once regarded as pathognomonic for tuberous sclerosis complex are now known to be less specific. No single sign is present in all affected patients, and there is no proof that any single clinical or radiographic sign is absolutely specific for tuberous sclerosis complex. Accordingly, the clinical and radiographic features of tuberous sclerosis complex have now been divided into major and minor categories based on the apparent degree of specificity for tuberous sclerosis complex of each feature. A definitive diagnosis of tuberous sclerosis complex now requires two or more distinct types of lesions, rather than multiple lesions of the same type in the same organ system. Although diagnosis on purely clinical grounds can continue to be difficult in a few patients, there should be little doubt about the diagnosis for those individuals who fulfill these strict criteria. Couples with more than one child with tuberous sclerosis complex, no extended family history, and no clinical features of tuberous sclerosis complex are more likely to have germline mosaicism for tuberous sclerosis than nonexpression of the mutation. Germline mosaicism, while fortunately rare, will not be suspected from either diagnostic criteria or molecular testing until a couple has multiple affected children. Genetic counseling for families with one affected child should include a small (1% to 2%) possibility of recurrence, even for parents who have no evidence of tuberous sclerosis complex after a thorough diagnostic evaluation.

Germ-line mutational analysis of the TSC2 gene in 90 tuberous-sclerosis patients

Ninety patients with tuberous-sclerosis complex (TSC) were tested for subtle mutations in the TSC2 gene, by means of single-strand conformational analysis (SSCA) of genomic DNA. Patients included 56 sporadic cases and 34 familial probands. For all patients, SSCA was performed for each of the 41 exons of the TSC2 gene. We identified 32 SSCA changes, 22 disease-causing mutations, and 10 polymorphic variants. Interestingly, we detected mutations at a much higher frequency in the sporadic cases (32%) than in the multiplex families (9%). Among the eight families for which linkage to the TSC2 region had been determined, only one mutation was found. Mutations were distributed equally across the gene; they included 5 deletions, 3 insertions, 10 missense mutations, 2 nonsense mutations, and 2 tandem duplications. We did not detect an increase in mutations either in the GTPase-activating protein (GAP)-related domains of TSC2 or in the activating domains that have been identified in rat tuberin. We did not detect any mutations in the exons (25 and 31) that are spliced out in the isoforms. There was no evidence for correspondence between variability of phenotype and type of mutation (missense versus early termination). Diagnostic testing will be difficult because of the genetic heterogeneity of TSC (which has at least two causative genes: TSC1 and TSC2), the large size of the TSC2 gene, and the variety of mutations. More than half of the mutations that we identified (missense, small in-frame deletion, and tandem duplication) are not amenable to the mutation-detection methods, such as protein-truncation testing, that are commonly employed for genes that encode proteins with tumor-suppressor function.

On the surgical treatment of refractory epilepsy in tuberous sclerosis complex

The role of surgery in the treatment of refractory epilepsy (RE) in tuberous sclerosis complex (TSC) is poorly defined. Four patients with RE and TSC were evaluated for epilepsy surgery from 1994 to 1996. Three of four patients developed infantile spasms within 5 months of birth. These progressed to frequent complex partial and generalized tonic/myoclonic seizures refractory to antiepileptic drug therapy. Neuroimaging revealed typical findings of TSC including calcified lesions consistent with hamartomas. Clinical and EEG evidence suggested an epileptic focus near a prominent lesion in each child. This was confirmed using magnetic source imaging in 1 case. All patients underwent inpatient continuous video-EEG monitoring followed by temporal lobectomy or focal cortical resection with intraoperative EEG. Age at operation ranged from 5 to 13 years. Three out of 4 patients experienced a greater than 90% decrease in seizure activity. One patient continues to have rare complex partial seizures, and 1 has rare simple partial seizures. Tumor DNA analysis revealed mutations in the TSC1 gene in case 1 and the TSC2 gene in case 2; no mutations have been identified yet in cases 3 and 4. Temporal lobectomy and focal cortical resection can result in improved seizure control in patients with TSC and RE.

Chromosome 1p36 deletions: the clinical phenotype and molecular characterization of a common newly delineated syndrome

Deletions of the distal short arm of chromosome 1 (1p36) represent a common, newly delineated deletion syndrome, characterized by moderate to severe psychomotor retardation, seizures, growth delay, and dysmorphic features. Previous cytogenetic underascertainment of this chromosomal deletion has made it difficult to characterize the clinical and molecular aspects of the syndrome. Recent advances in cytogenetic technology, particularly FISH, have greatly improved the ability to identify 1p36 deletions and have allowed a clearer definition of the clinical phenotype and molecular characteristics of this syndrome. We have identified 14 patients with chromosome 1p36 deletions and have assessed the frequency of each phenotypic feature and clinical manifestation in the 13 patients with pure 1p36 deletions. The physical extent and parental origin of each deletion were determined by use of FISH probes on cytogenetic preparations and by analysis of polymorphic DNA markers in the patients and their available parents. Clinical examinations revealed that the most common features and medical problems in patients with this deletion syndrome include large anterior fontanelle (100%), motor delay/hypotonia (92%), moderate to severe mental retardation (92%), growth delay (85%), pointed chin (80%), eye/vision problems (75%), seizures (72%), flat nasal bridge (65%), clinodactyly and/or short fifth finger(s) (64%), low-set ear(s) (59%), ear asymmetry (57%), hearing deficits (56%), abusive behavior (56%), thickened ear helices (53%), and deep-set eyes (50%). FISH and DNA polymorphism analysis showed that there is no uniform region of deletion but, rather, a spectrum of different deletion sizes with a common minimal region of deletion overlap.

Molecular analysis of the human vitamin D binding protein (group specific component, Gc) in tuberous sclerosis complex (TSC)

Group specific component (Gc) is an abundant plasma protein whose functional role is not clearly established. Gc protein is synthesised in the liver and is known to bind vitamin D, vitamin D metabolites, and G actin; Gc protein is also implicated in macrophage activation. Several polymorphic electrophoretic variants of Gc protein are found in all human populations; the most common alleles are Gc-1f, Gc-1s, and Gc-2. In previous studies, Gc allele frequencies, determined using isoelectric focusing or immunofixation or both, were significantly different in patients with tuberous sclerosis complex (TSC) from matched controls, with an excess of Gc-2 in patients. Linkage association between Gc and TSC is unlikely since the Gc locus maps to chromosome 4q12, whereas the two common forms of TSC map to 9q34 and 16p13.1, respectively. However, a direct cause and effect relationship between Gc protein and TSC symptoms is possible. To investigate further the relationship between the Gc locus and TSC, two Gc restriction site polymorphisms, HaeIII and StyI, were typed in 43 unrelated white subjects with TSC. The frequencies of the restriction site polymorphisms in the TSC patients did not differ from those in control populations. Therefore a direct association between Gc type and TSC is unlikely. The previously reported association was either spurious or the result of typing errors in plasma from subjects with underlying abnormalities in plasma proteins.

Mutations and polymorphisms in the tuberous sclerosis complex gene on chromosome 16

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder of benign tumor formation, hamartomata, and hamartias. TSC has been shown to be genetically heterogeneous, with one causative gene mapping to chromosome 9q (denoted TSC1) and at least one other gene on chromosome 16p (denoted TSC2). The TSC2 gene was recently cloned. We have tested 88 TSC probands with the TSC2 cDNA by Southern blotting searching for gross deletions/rearrangements/insertions. We detected two deletions and a rare intragenic polymorphic variant. This is a similar rate of mutation detection (2/88; 2.3%) to that in the original report (10/260/; 3.8%). The rare polymorphic variant was initially detected in the proband of a chromosome 9-linked multiplex TSC family. The polymorphism segregated with previously tested markers on chromosome 16 independently of the disease gene, verifying that the variation was unrelated to TSC status. We have also begun searching for subtle mutations by SSCA and direct sequencing. After screening three exons, we found two intragenic polymorphic variants. Both polymorphisms are common, making them useful for linkage studies in known affected families.

Brachmann-de Lange syndrome: autosomal dominant inheritance and male-to-male transmission

We report on familial occurrence of the Brachmann-de Lange syndrome (BDLS): a mildly affected father and his severely affected son and daughter who have different mothers. Both children are severely affected while the father has a much milder but definite BDLS phenotype. Our report documents the third example of male-to-male transmission and adds to the argument against exclusively maternal transmission in familial cases. In addition, our findings illustrate the occurrence of severe manifestations in cases of familial BDLS.

Report of a critical recombination further narrowing the TSC1 region

A large tuberous sclerosis multigenerational family segregating with markers on chromosome 9q from the TSC1 region was studied with a new highly polymorphic marker (designated A6) from the region. A critical affected person showed recombination with the marker, eliminating approximately 100 kilobases from the telomeric end of the critical region, which contains three genes and three to four additional exons for which the associated genes have not been delineated. This information serves to further the search for the TSC1 gene.

Cobblestone lissencephaly with normal eyes and muscle

Cobblestone lissencephaly is the characteristic brain malformation observed in Fukuyama congenital muscular dystrophy (FCMD), muscle-eye-brain disease (MEB), and Walker-Warburg syndrome (WWS). The diagnostic criteria for all three require the presence of congenital muscular dystrophy, and criteria for MEB and WWS require retinal abnormalities. We report three patients from two consanguineous families of Middle Eastern origin with cobblestone lissencephaly but no abnormalities of the eyes or muscle. Based on the current diagnostic criteria for the cobblestone lissencephaly syndromes, this disorder must be classified separately from the others, but it may well be allelic to MEB and WWS. Linkage studies have excluded the gene for this disorder from the region of the FCMD gene on chromosome 9q31-32.

Evaluation of candidate genes for familial brachydactyly

Type A1 brachydactyly in humans is a recognisable syndrome characterised by shortening of the middle phalanx of all digits with occasional fusion of the middle and terminal phalanges. The purpose of this study was to evaluate candidate genes for type A1 brachydactyly in two families with multiple affected members. Several classes of genes have been implicated in the control of distal limb development including homeobox containing genes (MSX1, MSX2) some members of the homeobox gene family, and genes encoding growth factors of the FGF, TGF, and PDGF families. Homeobox (Hox) genes are a family of developmental control genes activated early in embryogenesis that encode positional information along the anterior-posterior body axis and specify distinct spatial domains within developing limbs. Growth factor genes can regulate the proliferation and differentiation of various embryonic structures including limb buds and have been shown to influence Hox gene expression. Candidate genes HOXD, MSX1, MSX2, FGF-1, and FGF-2 were excluded in one family. The brachydactyly type A1 gene or locus was not found in either of the two families studied.

A 4-megabase YAC contig that spans the Langer-Giedion syndrome region on human chromosome 8q24.1: use in refining the location of the trichorhinophalangeal syndrome and multiple exostoses genes (TRPS1 and EXT1)

We have constructed a physical map covering over 4 Mb of human chromosome 8q24.1 and used this map to refine the locations of the genes responsible for Langer-Giedion syndrome. The map is composed of overlapping YAC clones that were identified and ordered in relation to sequence tagged sites mapped to the Langer-Giedion chromosomal region on somatic cell hybrids. The minimal region of overlap of Langer-Giedion syndrome deletions, previously identified by analysis of 15 patients, was placed on the map by analysis of 2 patients whose deletions define the endpoints. The chromosome 8 breakpoint of a balanced t(8;9)(q24.11;q33.3) translocation from a patient with trichorhinophalangeal syndrome (TRPS I) was found to be located just within the proximal end of the minimal deletion region. A deletion of 8q24.11-q24.3 in a patient with multiple exostoses was found to overlap the distal end of the LGS deletion region, indicating that the EXT1 gene is distal to the TRPS1 gene and supporting the hypothesis that Langer-Giedion syndrome is due to loss of functional copies of both the TRPS1 and the EXT1 genes.

COL5A1: fine genetic mapping and exclusion as candidate gene in families with nail-patella syndrome, tuberous sclerosis 1, hereditary hemorrhagic telangiectasia, and Ehlers-Danlos Syndrome type II

COL5A1, the gene for the alpha 1 chain of type V collagen, has been considered a candidate gene for certain diseases based on chromosomal location and/or disease phenotype. We have employed 3'-untranslated region RFLPs to exclude COL5A1 as a candidate gene in families with tuberous sclerosis 1, Ehlers-Danlos syndrome type II, and nail-patella syndrome. In addition, we describe a polymorphic simple sequence repeat (SSR) within a COL5A1 intron. This SSR is used to exclude COL5A1 as a candidate gene in hereditary hemorrhagic telangiectasia (Osler-Rendu-Weber disease) and to add COL5A1 to the existing map of "index" markers of chromosome 9 by evaluation of the COL5A1 locus on the CEPH 40-family reference pedigree set. This genetic mapping places COL5A1 between markers D9S66 and D9S67.

Variability of expression in tuberous sclerosis

We present three families in whom a diagnosis of tuberous sclerosis is difficult to secure and we review published reports about similar cases. Tuberous sclerosis has been reported to affect as many as 1 in 9400 subjects in the population. The manifestations of this disease vary not only between but also within families. Currently no reliable method of prenatal diagnosis is available. For these reasons, subjects known to be at 50% risk should be assessed scrupulously to clarify their status. These cases illustrate the difficulties in the clinical diagnosis of tuberous sclerosis and further reinforce the need for a molecular method of determining whether an at risk subject has the disease.

Symptomatic hyperammonemia caused by a congenital portosystemic shunt

A child with trisomy 21 had altered mental status and hyperammonemia at presentation and was found to have a congenital portosystemic shunt as a result of a congenital abnormality of the portal venous system. Anomalies of the portal venous system leading to portosystemic shunting, although they are infrequent, should be considered in the differential diagnosis of hyperammonemia.

Tuberous sclerosis complex: genetic aspects

Much has been learned about tuberous sclerosis complex (TSC) since it was described at the end of the nineteenth century. TSC was recognized to be a genetic disease with autosomal dominant inheritance in the early twentieth century. The prevalence in the general population is at least 1 in 10,000 with two-thirds of cases occurring sporadically and one-third of cases being familial. The disease exhibits variable expression which may cause mildly affected individuals to be undiagnosed. Because the aberrant or missing proteins which result in TSC have eluded investigators, a positional cloning approach has been pursued to find the mutated genes. Genetic linkages have been reported to chromosomes 9, 11, and 12. There is definite evidence for a TSC-causing locus on chromosome 9 which is thought to account for between one-third and one-half of all familial cases. Investigators have narrowed the location on chromosome 9 to approximately two megabases of physical distance. There is some evidence for a locus on chromosome 11 which probably accounts only for a small percentage of familial cases. The locus proposed on chromosome 12 was reported by a single group and has not been confirmed by other research groups. Evidence for genetic heterogeneity is abundant. There is definitely a TSC-causing locus on chromosome 9q (TSC-1) and there is at least one additional locus, maybe more than one. As the molecular basis of TSC unfolds, new insight will be gained about the protean nature of the disorder and the genetic heterogeneity.

Evidence for genetic heterogeneity in tuberous sclerosis: one locus on chromosome 9 and at least one locus elsewhere

Linkage of tuberous sclerosis complex (TSC), an autosomal dominant disorder, to markers on chromosome 9 was reported first in 1987. This assignment was confirmed by an international collaborative study that suggested more than one locus may be responsible for the phenotype. We studied 14 multigenerational TSC families (13 previously unreported) with markers for nine loci in the linked region of chromosome 9q32-q34. Our results confirm the previous reports that the genetic locus in one-third to one-half of families maps to chromosome 9. Comparison of clinical findings in the chromosome 9-linked families with those in the chromosome 9-unlinked families reveals only a higher incidence of ungual fibromata in the chromosome 9-linked families.

Linkage of an important gene locus for tuberous sclerosis to a chromosome 16 marker for polycystic kidney disease

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder of unknown aetiology that affects numerous body systems including skin, brain and kidneys. Some TSC has been linked to chromosome 9, additional TSC genes on chromosomes 11 and 12 have been proposed, but the majority of TSC families remain unlinked. Using TSC families in which data had excluded linkage to chromosome 9, we failed to detect linkage with loci on chromosomes 11, 12 and others. One marker examined was D16S283, the closest locus on the proximal side of the polycystic kidney disease type 1 (PKD1) gene. Linkage between TSC and D16S283 demonstrated a lod score of 9.50 at theta = 0.02 with one family independently presenting a lod score of 4.44 at theta = 0.05. These data reveal an important TSC locus near the region of PKD1 on chromosome 16p13.

Prenatal diagnosis of citrullinaemia: review of a 10-year experience including recent use of DNA analysis

Prenatal diagnosis of citrullinaemia has been accomplished by three different methods to date: (1) enzyme assay of cultured fetal cells; (2) quantification of citrulline in amniotic fluid supernatant; and (3) incorporation of [14C]citrulline into protein by cultured fetal cells. Our laboratory has used these methods to perform prenatal diagnosis for 28 fetuses over a 10-year period. More recently, DNA polymorphisms were used for prenatal diagnosis by linkage analysis. Of the 28 fetuses studied, 23 were predicted to be unaffected, four were predicted to be affected, and results were conflicting in one case where [14C]citrulline incorporation erroneously indicated an affected fetus but linkage analysis correctly predicted an unaffected fetus. Because of low levels of enzyme activity in heterozygotes and in certain amniotic fluid cell types, biochemical diagnosis of citrullinaemia is complicated by the risk of false affected results, although [14C]citrulline incorporation is relatively reliable. When informative, linkage analysis is the preferable method for cases with a 25 per cent risk. The risk of false affected results makes prenatal diagnosis for cases with less than 25 per cent risk of questionable value.