Distal Gastrointestinal Tract Research Articles

In Vivo Assessment of Cytochrome P450 3A4 and P-Glycoprotein Activity:Impact on Clinical Practice

Both bioavailability and clearance of most drugs for human use are strongly determined by hepatic and intestinal metabolism and transport. This is especially relevant for so-called narrow therapeutic index drugs, necessitating the use of therapeutic drug monitoring in many clinical settings. Cytochrome P450 3A4 (CYP3A4) is a key enzyme involved in over half of all phase I drug metabolism reactions and is abundantly present in the endoplasmic reticulum of both hepatocytes and enterocytes. P-glycoprotein (PGP), also known as MDR1 or ABCB1, is one of the first discovered and still most important active drug efflux pumps. Its localization on the apical cell membrane of hepatocytes zooming bile canaliculi and its relative distribution along the intestinal tract (PGP is mainly situated in the distal gastrointestinal tract, as opposed to CYP3A4, which is most prevalent in the proximal part) strongly suggests an interplay between these two proteins, optimizing the organisms defence against xenobiotics. To date, the main part of all research on CYP3A4 and PGP has been conducted in vitro and mostly using systems expressing either CYP3A4 or PGP. Since it has proven difficult to ‘scale up’ from in vitro results to clinically relevant phenomena such as potentially life threatening drug-drug interactions, several attempts have been made to bridge this ‘gap’ by assessing CYP3A4 and PGP activity in vivo. This review will focus on currently available methods for CYP3A4/PGP measurement in vivo and its impact on clinical practice, particularly in the field of clinical immunosuppression.

Pharmacologic Agents in the Management of Hypertension—Nisoldipine Coat‐Core

Nisoldipine coat-core (CC), a 1,4-dihydropyridine calcium antagonist, is indicated for the treatment of hypertension and may be used alone or in combination with other antihypertensive agents. The CC technology allows for extended delivery of the drug and once-daily dosing. Nisoldipine CC tablets are absorbed across the entire gastrointestinal tract, including the colon. Eighty percent of the total dose is in the slow-release outer coat, while the core has immediate-release characteristics suitable for absorption in the distal gastrointestinal tract. Numerous double-blind, randomized studies of this agent have been done in patients with hypertension. The use of nisoldipine CC reduced both clinic and ambulatory blood pressure to a similar degree when compared with angiotensin-converting enzyme (ACE) inhibitors, beta-blockers, and the calcium antagonists amlodipine and felodipine. The drug has also been studied in hypertensive African Americans and demonstrated equivalent efficacy to amlodipine. Tolerability of the drug is good, with the most common side effect of edema at a rate similar to other dihydropyridine calcium antagonists. Thus, results of more than a decade of clinical trial data support the use of nisoldipine CC as once-daily therapy for the treatment of hypertension.

Ingestion of High-Power Magnets: A New Concern in Children

Emergency physicians know that the potential for serious problems is small when children ingest button batteries, as long as the battery traverses the esophagus successfully. This report summarizes injuries to the more distal gastrointestinal tract associated …

Dietary Synergies in Appetite Control: Distal Gastrointestinal Tract

AbstractWOODS, STEPHEN C. Dietary synergies in appetite control: distal gastrointestinal tract.

Influence of colostrum deprivation and concurrent Cryptosporidium parvum infection on the colonization and persistence of Escherichia coli O157 : H7 in young lambs

Escherichia coli O157 : H7 and Cryptosporidium parvum infections of man have been associated with direct contact with small ruminants. Colostrum protects neonates against gastrointestinal pathogens, and orphan lambs, which are common on petting farms, may be deprived of this protection. In a recent study, it was demonstrated that high shedding of E. coli O157 : H7 by an 8-week-old goat kid was associated with coincidental C. parvum infection. Furthermore, both pathogens were co-located in the distal gastrointestinal tract. It was hypothesized that colostrum deprivation and pre-infection with C. parvum predisposed young ruminants to colonization and increased shedding of E. coli O157 : H7. To test this, 21 lambs 5 weeks of age were divided into four groups as follows: (A) colostrum-deprived and inoculated with E. coli O157 : H7, (B) colostrum-deprived and inoculated with C. parvum and then E. coli O157 : H7, (C) conventionally reared and inoculated with E. coli O157 : H7, (D) conventionally reared and inoculated with C. parvum and then E. coli O157 : H7. C. parvum was detected between 8 and 12 days post-inoculation in most of the infected lambs. At 24 h post-inoculation with E. coli O157 : H7, all lambs were shedding between 5 x 10(4) and 5 x 10(7) c.f.u. E. coli O157 : H7 per gram of faeces. E. coli O157 : H7 was shed in higher numbers in the groups pre-inoculated with C. parvum, whether conventionally reared or colostrum-deprived. Interestingly, for the colostrum-deprived lambs on day 3, a significant difference in shedding of E. coli O157 : H7 was observed (P = 0.038), with the lambs inoculated with E. coli alone yielding higher counts than those pre-inoculated with C. parvum. From day 15 onwards, shedding of E. coli O157 : H7 was highest from the colostrum-deprived C. parvum-infected lambs, then (in descending order of shedding) the colostrum-deprived lambs, the conventionally reared lambs infected with C. parvum, and the conventionally reared animals. In total, four animals were euthanized, two at 24 h and two at 96 h post inoculation with E. coli O157 : H7 (two conventionally reared and two colostrum-deprived). All animals euthanized were from groups pre-inoculated with C. parvum prior to challenge with E. coli O157 : H7. On examination of tissues, in three of the four animals examined, multifocal attaching and effacing lesions were observed in the caecum, colon, rectum and at the recto-anal junction, and were confirmed by immunohistochemistry to be associated with E. coli O157 : H7.

Killing the Messenger in the Nick of Time: Persistence of Breast Milk sCD14 in the Neonatal Gastrointestinal Tract

Human breast milk contains several proteins that supplement the newborn mucosal defense system and prevent gastrointestinal illnesses. One of these recently identified breast milk proteins is soluble CD14 (sCD14). By being an important component of the lipopolysaccharide (LPS) receptor complex, it has been suggested that breast milk sCD14 could stimulate the newborn immune system and help reduce gastrointestinal Gram-negative infections. However, to deliver its potential immune benefits to the neonate, sCD14 would have to survive the passage through the gastrointestinal tract and retain its biologic activity. We analyzed the presence of breast milk sCD14 in the neonatal digestive system and found breast milk sCD14 to be absent from the stools of breast-fed infants. In vitro digestion analysis with simulated gastric and pancreatic fluids revealed that sCD14 is likely to survive the pepsin digestion but is more prone to been nicked and digested by pancreatin. These findings suggest that the presence of intact breast milk sCD14 in the upper digestive system could promote innate immunity in this low bacteria density lumen. The low concentration of sCD14 in the LPS-rich environment of the distal gastrointestinal tract (i.e. commensal microflora) could prevent excessive inflammation.

An Animal Model to Study Digesta Passage in Different Compartments of the Gastro-Intestinal Tract (GIT) as Affected by Dietary Composition

An animal model was developed which allows the testing of the effect of dietary factors on digesta passage in the stomach, the small intestine, the large intestine and the total gastrointestinal tract in growing pigs (46 - 119 kg BW). Rates of digesta passage were determined using a simultaneous pulse dose of titanium dioxide (TiO2) mixed in the diet and suspensions of chromiumIIIoxide (Cr2O3) and barium sulphate (BaSO4) in saline, introduced via cannulae to the proximal jejunum and to the terminal ileum, respectively. Faecal recovery of each of the markers was quantified using an one-compartment model from which the transit times (TT) of the markers were derived. The TT of TiO2 represented the passage of digesta over whole gastro-intestinal tract (GIT) whereas the TT of Cr2O3 and BaSO4 represented the TT over the small plus large intestines and over the large intestines, respectively. The TT over the stomach and small intestine were estimated from the TT determined over the whole GIT and over the two sections of the GIT. Besides a control diet (C diet), three diets were offered differing in the contents of non starch polysaccharides (NSP) and water-holding capacity (WHC). A combination of palm kernel expeller and toasted soy bean hulls were included in the diet as NSP sources (NSP diet) and hydrolysed maize starch was included to elevate WHC (WHC diet). The fourth diet had both a high NSP content and a high WHC content (NSP plus WHC diet). The mean transit time (MTT) of the marker passing the whole GIT was on average 75 h and NSP significantly decreased TT over the total GIT and through the large intestines (P < 0.05). In contrast, NSP tended to increase the TT of the stomach contents (P < 0.10). The effects of WHC were smaller and limited to tendencies for a decrease of the TT in the large intestines (P < 0.10) and an increase of the TT in the small intestine (P < 0.10). It is concluded that NSP and to a lesser extent WHC, have opposite effects on digesta passage in the proximal and distal GIT, respectively. The animal model developed in the present study seems a valuable method to test the effect of dietary factors on the passage of digesta. Keywords: Digesta, passage, gastro-intestinal tract, dietary composition, microbial activity, fermentation

Urinary retention during sacral nerve stimulation for faecal incontinence: report of a case

Sacral nerve stimulation (SNS) was proposed for the treatment of patients with urologic symptoms in 1967 but was not used until 1981. SNS has also proven to be a promising treatment in idiopathic faecal incontinence when conventional treatments have failed. The modality has been used for faecal incontinence since the mid-1990s. Eighty percent of the patients who were selected for percutaneous nerve evaluation (PNE) because of faecal incontinence report an improvement in the symptoms and qualify for a permanent implantation. Accordingly, SNS is now used for faecal incontinence and urologic symptoms. Reflex interactions between the bladder and the distal gastrointestinal tract are well known. The present case shows that SNS for faecal incontinence may significantly influence bladder function.

The Role of the Vagal Nerve in Peripheral PYY3–36-Induced Feeding Reduction in Rats

Peptide YY (PYY), an anorectic peptide, is secreted postprandially from the distal gastrointestinal tract. PYY(3-36), the major form of circulating PYY, binds to the hypothalamic neuropeptide Y Y2 receptor (Y2-R) with a high-affinity, reducing food intake in rodents and humans. Additional gastrointestinal hormones involved in feeding, including cholecystokinin, glucagon-like peptide 1, and ghrelin, transmit satiety or hunger signals to the brain via the vagal afferent nerve and/or the blood stream. Here we determined the role of the afferent vagus nerve in PYY function. Abdominal vagotomy abolished the anorectic effect of PYY(3-36) in rats. Peripheral administration of PYY(3-36) induced Fos expression in the arcuate nucleus of sham-operated rats but not vagotomized rats. We showed that Y2-R is synthesized in the rat nodose ganglion and transported to the vagal afferent terminals. PYY(3-36) stimulated firing of the gastric vagal afferent nerve when administered iv. Considering that Y2-R is present in the vagal afferent fibers, PYY(3-36) could directly alter the firing rate of the vagal afferent nerve via Y2-R. We also investigated the effect of ascending fibers from the nucleus of the solitary tract on the transmission of PYY(3-36)-mediated satiety signals. In rats, bilateral midbrain transections rostral to the nucleus of the solitary tract also abolished PYY(3-36)-induced reductions in feeding. This study indicates that peripheral PYY(3-36) may transmit satiety signals to the brain in part via the vagal afferent pathway.

Host-bacterial interactions in inflammatory bowel disease.

Large numbers of different bacterial species are resident in the lumen of the distal gastrointestinal tract. The normal intestinal host-microbial interactions are not well understood, but the relationship is generally believed to be either mutually beneficial or beneficial to one without disadvantage to the other. Animal model and clinical studies suggest that IBD (inflammatory bowel disease) may develop in a susceptible individual when the normal host-bacterial relationship is dysregulated. In addition to rodent models, this article reviews studies that have investigated the cellular and molecular mechanisms of interactions between intestinal mucosal cells and the resident luminal bacteria in healthy individuals and patients with ulcerative colitis and Crohn's disease. Mechanisms by which the intestinal mucosa is able to avoid pro-inflammatory responses to commensal bacteria (and their products) but able to respond appropriately to luminal pathogens is currently an area of active investigation. Such studies are beginning to provide important clues regarding possible alterations in the mucosa that lead to the development of pro-inflammatory responses to resident bacteria in patients with IBD. Approaches to alter the intestinal microflora for therapeutic purposes and their potential mechanisms of action are also discussed.

Clinical implications of COX-1 and/or COX-2 inhibition for the distal gastrointestinal tract.

Side effects of the distal gastrointestinal tract after NSAID use are common and more frequent than previously recognized. Increased mucosal permeability and mucosal inflammation are often silent but appear after NSAID treatment with most dual COX inhibitors. Other clinical manifestations include: anemia, occult blood loss, malabsorption, protein-loss, ileal dysfunction, diarrhea, mucosal ulceration and strictures due to diaphragm disease. More common complications are lower gastrointestinal bleeding and perforation, which represent at least one third of all gastrointestinal complications observed with NSAID use. Studies with selective COX-2 inhibitors have shown that, in the short term, these agents do not increase mucosal permeability or induce anemia due to occult bleeding and that, when compared to dual COX inhibitors, lower gastrointestinal complications may be reduced by 50%. In order to minimize the impact of these side effects, it is important to increase the current standards of suspicion by physicians who treat these patients, since drug discontinuation may further reduce damage, and clinical experience with agents that may prevent or treat distal tract damage is very limited. From this perspective, selective COX-2 inhibitors may be the drugs of choice in the high-risk patient that needs NSAIDs. Another important area of uncertainty is the impact of NSAID use in patients with inflammatory bowel diseases. Data from different animal models of inflammatory bowel disease suggest that inhibition of both COX-1 and COX-2 derived prostaglandins affects the severity of the mucosal inflammation. However, current epidemiological and clinical data are contradictory. Since many patients.

EPR spectroscopy and imaging of oxygen: applications to the gastrointestinal tract.

EPR imaging has emerged as an important tool for noninvasive three-dimensional (3D) spatial mapping of free radicals in biological tissues. Spectral-spatial EPR imaging enables mapping of the spectral information at each spatial position, and, from the observed linewidth, the localized tissue oxygenation can be mapped. We report the application of EPR imaging techniques enabling 3D spatial and spectral-spatial EPR imaging of small animals. This instrumentation, along with the use of a biocompatible charcoal oximetry-probe suspension, enabled 3D spatial imaging of the gastrointestinal (GI) tract, along with mapping of oxygenation in living mice. By using this technique, the oxygen tension was mapped at different levels of the GI tract from the stomach to the rectum. The results clearly show the presence of a marked oxygen gradient from the proximal to the distal GI tract, which decreases after respiratory arrest. This technique for in vivo mapping of oxygenation is a promising method, enabling the noninvasive imaging of oxygen within the normal GI tract. This method should be useful in determining the alterations in oxygenation associated with disease.

Evaluation of Pulsincap™ to provide regional delivery of dofetilide to the human GI tract

Pulsincap™ formulations designed to deliver a dose of drug following a 5-h delay were prepared to evaluate the capability of the formulation to deliver dofetilide to the lower gastrointestinal (GI) tract. By the expected 5-h release time, the preparations were well dispersed throughout the GI tract, from stomach to colon. Plasma analysis permitted drug absorption to be determined as a function of GI tract site of release. Dofetilide is a well-absorbed drug, but showed a reduction in observed bioavailability when delivered from the Pulsincap™ formulations, particularly at more distal GI tract sites. Dispersion of the drug from the soluble excipient used in this prototype formulation relies on a passive diffusion mechanism and the relevance of this factor to the reduced extent and consistency of absorption from the colon is discussed. In these studies the effects of the degree of dispersion versus the site of dispersion could not be ascertained; nevertheless the scintigraphic analysis demonstrated good in vitro–in vivo correlation for time of release from Pulsincap™ preparations. The combination of scintigraphic and pharmacokinetic analysis permits identification of the site of drug release from the dosage form and pharmacokinetic parameters to be studied in man in a non-invasive manner.

SQUAMOUS CELL CARCINOMA OF THE ANAL CANAL AND ANAL MARGIN

Squamous cell carcinomas of the anal canal and margin are relatively uncommon neoplasms of the distal gastrointestinal tract and surrounding skin. The major risk factors for tumor development have been defined through various epidemiologic studies. Randomized, phase III trials have defined the standard of care for anal cancer tumors to be a combined modality approach of radiation therapy and chemotherapy. This nonsurgical, organ-sparing regimen results in good anal sphincter function in the majority of patients, and treatment efficacy is favorable when compared with historic surgical series. Anal margin tumors are staged and treated as skin cancers, with a more favorable prognosis.

Interstitial cells of Cajal: primary targets of enteric motor innervation.

For many years morphologists have noted the close relationship between interstitial cells of Cajal (ICC) and nerve fibers within the tunica muscularis of gastrointestinal (GI) organs. These observations led to speculations about a role for ICC in mediating neural inputs to the GI tract. Immunohistochemical and functional studies demonstrated the presence of receptors for the neurotransmitters utilized by enteric motor neurons, and changes in second messengers in ICC after field stimulation of intrinsic enteric neurons showed that ICC were functionally innervated in GI muscles. Recent double labeling experiments have shown that both excitatory and inhibitory enteric motor neurons are closely associated with ICC in the deep muscular plexus (IC-DMP) of the small intestine and intramuscular ICC (IC-IM) of the proximal and distal GI tract. Enteric motor neurons form synaptic-like structures with IC-IM and IC-DMP. Far fewer close contacts are found between enteric motor neurons and smooth muscle cells. Experiments on W/W(V) mutants that lack IC-IM in the stomach, lower esophageal sphincter, and pylorus have shown that these ICC are critical components of the neuromuscular junction. Cholinergic excitatory and nitrergic inhibitory neurotransmission are severely decreased in tissues lacking IC-IM, yet there is no loss of cholinergic or nitrergic neurons in W/W(V) mutants. These data suggest that either the post-junctional mechanisms responsible for receiving and transducing neurotransmitter signals are specifically expressed by ICC, or that the large extracellular spaces typically between nerve terminals and smooth muscle cells may not allow effective concentrations of neurotransmitters to reach receptors expressed by smooth muscle cells. These findings indicate an important role for certain classes of ICC in enteric neurotransmission and predict that loss of ICC in human motor disturbances may significantly compromise neural regulation of GI motility.

A single-nucleotide polymorphic variant of the RET proto-oncogene is underrepresented in sporadic Hirschsprung disease.

Hirschsprung disease (HSCR) is an inherited disorder characterised by absence of intrinsic ganglion cells in the distal gastrointestinal tract. Different susceptibility genes, involved in either the Ret-tyrosine kinase or the endothelin signalling pathways, contribute to HSCR phenotype. Interestingly, alterations of these genes are detected in only 30-50% of all HSCR patients, suggesting the involvement of modifier genes and/or additional genetic or environmental risk factors. In complex disorders common polymorphic variants can be associated with the disease phenotype, thus modifying the risk of recurrence. To investigate whether sequence variants of the RET proto-oncogene may be associated with the development of the HSCR phenotype, we analysed 92 Italian patients for the 2508C > T synonymous substitution in exon 14 (S836S) finding that the T allele is clearly less frequent than in control individuals (Fisher exact test P = 0.0002). On the other hand, this RET variant allele is overrepresented in patients affected with medullary thyroid carcinoma. Assuming a direct effect of this single-nucleotide polymorphism in predisposing to RET associated pathologies, we have performed functional tests which excluded any possible involvement of the C and T alleles in DNA-protein binding, transcript stability and RNA splicing and editing.

In situ electrolyte interactions in a disk-compressed configuration system for up-curving and constant drug delivery

A new approach in drug delivery system design for meeting the needs that are associated with certain circadian variations is presented. The system is comprised of a pure compressed drug disk, which is encased by a polymeric coat using hydroxypropylmethylcellulose or polyethylene oxide. Within the polymeric coat, a physiologically acceptable binary electrolyte combination such as sodium deoxycholate and adipic acid is disposed. Through this process and upon exposure to dissolution media, ionic interactions occur and a texturally variable matrix is manifested in the form of ‘peripheral stiffening’ with self-correcting boundaries as demonstrated by texture analysis studies. The peripheral boundaries erode and progressively shift toward the disk-core, thus constantly reducing the diffusional pathlength with the resultant up-curving kinetics. Utilizing these mechanisms, a lag time is induced and drug is delivered over a 24-h period in one of two ways namely, in an up-curving or constant manner for drug models theophylline and diltiazem hydrochloride with water solubilities of 0.85% and >50% at 25°C, respectively. It appears that for both sparingly and highly soluble drugs, sum of the dissolution/diffusion rates, dynamics of diffusional pathlength and system erosion rate control the release process. The heterogeneous nature of changes in coat thickness, stiffening dynamics and erosion rate in relation to disk geometry is discussed. The developed technology has potential to provide release patterns, compatible with specific chronophysiological conditions, and overcome the absorption-limited capacity of the distal gastrointestinal tract.

A comparative histopathologic evaluation of the effects of three different solutions used for whole bowel irrigation: An experimental study

Purpose: Although whole bowel irrigation (WBI) is a widely used method of bowel preparation in daily surgical practice, almost nothing is known about the histopathologic alterations caused by WBI and whether these differences have any detrimental effect on the outcome of gastrointestinal surgical procedures. Therefore, an experimental study has been conducted to evaluate and compare the effects of WBI with various solutions on the histology of gastrointestinal tract. Methods: During the experimental procedures animals were divided into 4 groups consisting of 8 animals each as follows: group A, WBI performed by using isotonic saline solution; group B, WBI performed by using an isoosmolar solution containing polyethylene glycol (PEG); group C, WBI performed by using Lactated Ringer's solution; group D, Animals that were not irrigated but sham operations that were performed served as controls. Four hours after WBI the animals underwent laparotomy and a segment of transverse colon with intact vascular peduncle was prepared. After waiting for 30 minutes, specimens from duodenum, small intestine, large bowel, colonic segment, and liver were obtained from each animal. Histopathologically, all of the specimens were evaluated and graded by 3 parameters including congestion, edema, and inflammation. Results: Although varying degrees of congestion, edema, and inflammation were encountered from all of the specimens of group A, B, and C, only slight congestion was noted in all specimens of group D. The difference between group D and other groups was statistically very significant (P <.001). When the sections from duodenums of groups were evaluated, the degree of congestion, edema, and inflammation were found to be moderate in group B, mild-moderate in group A, and mild in group C. Histopathologic examinations of specimens of the small, large bowel, and isolated colonic segment showed severe congestion, edema, and inflammation in group A, moderate-mild in group B, and mild in group C. The difference between A and B, A and C, and A and D was statistically significant (P <.01). Although severe congestion was encountered in liver specimens of group A, only mild congestion was encountered in groups B and C (P =.0001). The matched durations of irrigations and total volume of irrigation solutions were found to be not related with the difference in histopathologic findings. Conclusions: WBI has induced varying degrees of histopathologic alterations from mild to severe in the rat gastrointestinal tract. Lactated Ringer's solution and PEG solution have induced the least alterations. Therefore, WBI with Lactated Ringer's solution and PEG solution seem to be safe alternatives of mechanical bowel preparation before elective large bowel surgery. Because saline solution has caused detrimental alterations in distal gastrointestinal tract histology, WBI with saline solution seems to be unadvisable. J Pediatr Surg 35:564-568. Copyright © 2000 by W.B. Saunders Company.

Noninvasive measurement of anatomic structure and intraluminal oxygenation in the gastrointestinal tract of living mice with spatial and spectral EPR imaging.

EPR imaging has emerged as an important tool for noninvasive three-dimensional (3D) spatial mapping of free radicals in biological tissues. Spectral-spatial EPR imaging enables mapping of the spectral information at each spatial position, and, from the observed line width, the localized tissue oxygenation can be mapped. We report the development of EPR imaging instrumentation enabling 3D spatial and spectral-spatial EPR imaging of small animals. This instrumentation, along with the use of a biocompatible charcoal oximetry-probe suspension, enabled 3D spatial imaging of the gastrointestinal (GI) tract, along with mapping of oxygenation in living mice. By using these techniques, the oxygen tension was mapped at different levels of the GI tract from the stomach to the rectum. The results clearly show the presence of a marked oxygen gradient from the proximal to the distal GI tract, which decreases after respiratory arrest. This technique for in vivo mapping of oxygenation is a promising method, enabling the noninvasive imaging of oxygen within the normal GI tract. This method should be useful in determining the alterations in oxygenation associated with disease.

The Sox10Dom Mouse: Modeling the Genetic Variation of Waardenburg-Shah (WS4) Syndrome

Hirschsprung disease (HSCR) is a multigenic neurocristopathy clinically recognized by aganglionosis of the distal gastrointestinal tract. Patients presenting with aganglionosis in association with hypopigmentation are classified as Waardenburg syndrome type 4 (Waardenburg-Shah, WS4). Variability in the disease phenotype of WS4 patients with equivalent mutations suggests the influence of genetic modifier loci in this disorder. Sox10(Dom)/+ mice exhibit variability of aganglionosis and hypopigmentation influenced by genetic background similar to that observed in WS4 patients. We have constructed Sox10(Dom)/+ congenic lines to segregate loci that modify the neural crest defects in these mice. Consistent with previous studies, increased lethality of Sox10(Dom)/+ animals resulted from a C57BL/6J locus(i). However, we also observed an increase in hypopigmentation in conjunction with a C3HeB/FeJLe-a/a locus(i). Linkage analysis localized a hypopigmentation modifier of the Dom phenotype to mouse chromosome 10 in close proximity to a previously reported modifier of hypopigmentation for the endothelin receptor B mouse model of WS4. To evaluate further the role of SOX10 in development and disease, we have performed comparative genomic analyses. An essential role for this gene in neural crest development is supported by zoo blot hybridizations that reveal extensive conservation throughout vertebrate evolution and by similar Northern blot expression profiles between mouse and man. Comparative sequence analysis of the mouse and human SOX10 gene have defined the exon-intron boundaries of SOX10 and facilitated mutation analysis leading to the identification of two new SOX10 mutations in individuals with WS4. Structural analysis of the HMG DNA-binding domain was performed to evaluate the effect of human mutations in this region.