Stress imaging in patients with a Fontan circulation: A systematic review.

INTRODUCTION: The aims of this study were to provide an overview of the cardiac stress response in Fontan patients and of the use, safety and clinical value of stress imaging in Fontan patients. METHODS: Studies evaluating cardiac function using stress imaging in Fontan patients published up until 12 December 2021 were included in this review. RESULTS: From 1603 potential studies, 32 studies met the inclusion criteria. In total, stress imaging tests of 728 Fontan patients were included. Cardiac function was most often measured using physical stress (61%), all other studies used dobutamine-induced stress. Stroke volume (SV) increased in most studies (71%), mean SV at rest ranged from 27 mL/m2 to 60 mL/m2 versus 27 mL/m2 to 101 mL/m2 during stress, and increased with an average of 4%. Ejection fraction increased in almost all studies, whereas both end-systolic volume and end-diastolic volume decreased during stress. Higher heart rates were obtained with physical stress (82-180) compared to dobutamine induced stress (73-128). Compared to controls, increases in heartrate and SV were lower and end-diastolic volume decreased abnormally in 75% of reporting studies. No major adverse events were reported. Poorer cardiac stress response was related to decreased exercise capacity and higher risk for long-term (adverse) outcomes in Fontan patients. DISCUSSION: Cardiac stress response in Fontan patients differs from healthy subjects, reflected by lower increases in heart rate, diminished preload and decreased cardiac output, especially during higher levels of exercise. Stress imaging is safe, however the added clinical value needs to be investigated in more detail.

Differential vasodilation of human placental and myometrial arteries related to myofilament Ca(2+)-desensitization and the expression of Hsp20 but not MYPT1.

Endothelial-dependent regulation of vascular tone occurs in part via protein kinase G1α-mediated changes in smooth muscle myofilament sensitivity to Ca(2+). Tissue-specific differences in PKG-dependent relaxation have been attributed to altered expression of myofilament-associated proteins that are substrates for PKG binding. These include the alternative splicing of the myosin targeting subunit (MYPT1) of myosin light chain phosphatase to yield leucine zipper positive (LZ(+)) and negative (LZ(-)) isovariants, with the former being required for PKG-mediated relaxation, and/or altered expressions of telokin, vasodilator-stimulated phosphoprotein (VASP) or heat shock protein Hsp20. During human pregnancy the uterine and placental circulations remain distinct entities and, as such, their mechanisms of vascular tone regulation may differ. Indeed, the sensitivity of myometrial arteries to endothelial-dependent agonists has been suggested to be greater than that of placental arteries. We tested the hypothesis that this was related to tissue-specific changes in PKG-mediated myofilament Ca(2+)-desensitization and/or the expressions of PKG-interacting myofilament-associated proteins. Permeabilized human placental and myometrial arteries were constricted with maximal activating Ca(2+) (pCa 4.5), or sub-maximal Ca(2+) (pCa 6.7) and the thrombane mimetic U46619, and exposed to 8-Br-cGMP. In each case, relaxation was significantly greater in myometrial arteries (e.g. relaxation in pCa 4.5 to 8-Br-cGMP was 49 ± 9.7%, n = 7) than placental arteries (relaxation of 23 ± 6.6%, n = 6, P < 0.05). MYPT1 protein levels, or MYPT1 LZ(+)/LZ(-) mRNA ratios, were similar for both artery types. Of other proteins examined, only Hsp20 expression was significantly elevated in myometrial arteries than placental arteries. These results demonstrate that the reduced human placental artery relaxation to PKG stimulation lies partly at the level of myofilament (de)activation and may be related to a lower expression of Hsp20 than in myometrial arteries.

Clonus is explained from increased reflex gain and enlarged tissue viscoelasticity.

Upper motor neuron diseases (UMND), such as stroke and spinal cord injury (SCI), are assumed to produce alterations in muscle tissue in association with neural damage. Distinguishing between these two factors is of clinical importance in choosing appropriate therapy. We studied the effect of changes in the gain of the Ia reflex pathway and tissue viscoelasticity on the emergence, frequency, and persistence of ankle clonus: a clinically significant, involuntary oscillatory movement disorder. Monte Carlo simulations were performed to explain our experimental observations in patients with stroke (n = 3) and SCI (n = 4) using a nonlinear antagonistic muscle model of the human ankle joint. Ia reflex gain was varied by changing motor unit pool threshold and gain, and passive tissue viscosity and elasticity were varied by changing optimal muscle length. Tissue viscoelasticity appeared to have a strong effect on the emergence and persistence of clonus. Observed frequencies of ankle movement, prior to and after the experimental intervention of a sudden damper, was predicted by the model. The simulations revealed that reflex gains were largest in patients with the largest tissue viscoelasticity. We conclude that ankle clonus in stroke and SCI is the result of a combination of, and suggests a relation between, (i) a decrease in threshold and an increase in gain of the motor unit pool and (ii) a decrease in optimal muscle length.

Factors associated with antenatal care utilization among rural women in Lao People's Democratic Republic.

This study aims at exploring factors related to the antenatal care (ANC) utilization in rural areas of Lao PDR. A quantitative, cross-sectional interview study was conducted in the Khammouane and Champasack provinces. The study population comprised all currently pregnant women 15-45 years of age with a gestational period beyond 32 weeks plus all women who had given birth during the last 12 months. With the informed consent of all eligible women, 460 respondents were included in the study and interviewed using a structured questionnaire. Multiple logistic regression analysis was applied to determine factors significantly related to ANC use. Fifty-one percent of the respondents had at least one ANC visit. Among the users, 63% had visited ANC three times or more but only 28% attended during the first trimester. After adjusting for other factors, using a 95% Confidence Interval (CI), statistically significant associations were found between ANC use and the following factors: women whose husbands were salaried employees (OR=2.66, CI=1.45-4.88); women younger than 18 years old at first pregnancy (OR 0.56, CI=0.28-0.97); women perceiving ANC as somewhat useful (OR=2.88, CI=1.26-6.61) or very useful (OR=7.45, CI=3.59-15.46). Awareness of the usefulness of ANC was related to more frequent use and could be one focus of community intervention to increase utilization.

Mutations in LAMB2 causing a severe form of synaptic congenital myasthenic syndrome.

BACKGROUND: We describe a severe form of congenital myasthenic syndrome (CMS) associated with congenital nephrosis and ocular malformations caused by two truncating mutations in the gene encoding the laminin beta2 subunit (LAMB2). METHODS AND RESULTS: Mutational analysis in the affected patient, who has a history of a serious untoward reaction to treatment with acetylcholinesterase inhibition, revealed two frame-shifting heteroallelic mutations, a maternally inherited 1478delG and a paternally inherited 4804delC. An anconeus muscle biopsy demonstrated a profound distortion of the architecture and function of the neuromuscular junction, which was strikingly similar to that seen in mice lacking laminin beta2 subunit. The findings included: pronounced reduction of the axon terminal size with encasement of the nerve endings by Schwann cells, severe widening of the primary synaptic cleft and invasion of the synaptic space by the processes of Schwann cells, and moderate simplification of postsynaptic folds and intact expression of the endplate acetylcholinesterase. The endplate potential quantal content was notably reduced, while the frequencies and amplitudes of miniature endplate potentials were only moderately diminished and the decay phases of miniature endplate potentials were normal. Western blot analysis of muscle and kidney tissue and immunohistochemistry of kidney tissue showed no laminin beta2 expression. CONCLUSION: This case, which represents a new type of synaptic CMS, exemplifies the wide variability of phenotypes associated with LAMB2 mutations and underscores the fundamental role that laminin beta2 plays in the development of the human neuromuscular junction.

Prediction of hypotension during spinal anesthesia for Cesarean section and its relation to the effect of crystalloid or colloid preload.

BACKGROUND: If parturients prone to develop caval compression in the supine position were identified before delivery, this might be a method of predicting hypotension during caesarean section under spinal anesthesia. Colloid preloading is superior to crystalloid in reducing the risk for spinal anesthetic-induced hypotension. It is postulated that parturients preoperatively susceptible to the supine position would benefit the most from colloid preloading. METHODS: Fifty-five healthy parturients scheduled for elective cesarean section under spinal anesthesia were preoperatively investigated with a supine stress test with measurement of maternal heart rate, blood pressure, right uterine artery pulsatility index and symptoms in the left lateral and supine positions. They were then randomized to receive a colloid or crystalloid preload before anesthesia. RESULTS: The stress test was positive, indicating a reduced tolerance to the supine position, in 36%. The sensitivity and specificity of the stress test for clinically significant hypotension (symptomatic hypotension) for patients randomized to the crystalloid group (n=25) were 69 and 92% respectively. Patients with a positive stress test receiving a crystalloid preload showed a higher frequency of hypotension compared to all other groups, 90% vs. 33%, (P=0.003) and also a greater need for ephedrine, mean dose (SD): 20.0 (9.7) vs. 8.4 (9.0) mg (P=0.002). CONCLUSIONS: Pregnant women with a positive preoperative supine stress test constitute a subset at increased risk for clinically significant hypotension during cesarean delivery under spinal anesthesia. These women seem more likely to benefit from prophylactic colloid solution than women with a negative stress test.

Colloid vs. crystalloid preloading to prevent maternal hypotension during spinal anesthesia for elective cesarean section.

BACKGROUND: Hypotension associated with spinal anesthesia for cesarean section is still a clinical problem. Colloid solutions seem preferable to crystalloid solutions for preloading. In most studies the overall rate of hypotension is reported. Few studies have, however, investigated the maternal and neonatal consequences of different levels of maternal hypotension. METHODS: In this randomized, double-blinded study 110 patients presenting for elective cesarean section received either 1000 ml acetated Ringer's solution or 1000 ml 3% dextran 60 solution immediately before spinal anesthesia. The effect on overall hypotension, clinically significant hypotension (hypotension associated with maternal discomfort defined as nausea, retching/vomiting, dizziness or chest symptoms) and severe hypotension (systolic arterial pressure <80 mmHg) was studied. RESULTS: Dextran reduced the incidence of overall hypotension from 85 to 66% (P=0.03), reduced the incidence of clinically significant hypotension from 60 to 30% (P=0.002) and reduced the incidence of severe hypotension from 23 to 3.6% (P=0.004) compared to Ringer's solution. There were neither differences in neonatal outcome between treatment groups nor between neonates grouped after severity of maternal hypotension. CONCLUSION: Clinically significant hypotension seems to be a more suitable outcome variable than overall hypotension. The protective effect of the colloid solution increased with increased severity of hypotension.

Serial exercise performance in children with surgically corrected congenital aortic stenosis.

We examined serial exercise test performance in children with congenital aortic stenosis (AS) treated surgically compared to that of nonoperated children with mild to moderate AS. Maximal treadmill exercise data were assessed in 21 children 5.5 +/- 3.8 years after aortic valve (AO) surgery. Patients had undergone the Ross procedure (n = 6) or previous aortic valvotomy, balloon valvuloplasty, or neonatal aortic valvotomy (n = 15). Follow-up treadmill tests were conducted 3.7 +/- 2.8 years later. Data were compared to those of 19 nonoperated AS patients (mean gradient by echocardiogram <50 mmHg). These patients were exercised 3.6 +/- 3.2 years apart. Endurance time, heart rate, systemic blood pressure, and electrocardiogram were compared as repeated measures between tests and to age- and sex-matched normative data. Postsurgical children with AS had normal endurance times despite low peak heart rates on the initial test, and they maintained endurance over time. Nonoperated children with mean AO gradients <50 mmHg also had normal endurance times on the initial test but increased endurance over 3.6 years. Children with operated and nonoperated AS were able to reach or exceed normal endurance times, which may make it difficult to achieve compliance to imposed activity restrictions in this population.

Inhibition of selectin-mediated cell adhesion and prevention of acute inflammation by nonanticoagulant sulfated saccharides. Studies with carboxyl-reduced and sulfated heparin and with trestatin a sulfate.

Selectins play a major role in the inflammatory reaction by initiating neutrophil attachment to activated vascular endothelium. Some heparin preparations can interact with L- and P-selectin; however, the determinants required for inhibiting selectin-mediated cell adhesion have not yet been characterized. We now report that carboxyl-reduced and sulfated heparin (prepared by chemical modifications of porcine intestinal mucosal heparin leading to the replacement of carboxylates by O-sulfate groups) and trestatin A sulfate (obtained by sulfation of trestatin A, a non-uronic pseudo-nonasaccharide extracted from Streptomyces dimorphogenes) exhibit strong anti-P-selectin and anti-L-selectin activity while lacking antithrombin-mediated anticoagulant activity. In vitro experiments revealed that both compounds inhibited P-selectin- and L-selectin-mediated cell adhesion under laminar flow conditions. Moreover, carboxyl-reduced and sulfated heparin and trestatin A sulfate were also active in vivo, as assessed by experiments showing 1) that microinfusion of trestatin A sulfate reduced by 96% leukocyte rolling along rat mesenteric postcapillary venules and 2) that both compounds inhibited (by 58-81%) neutrophil migration into thioglycollate-inflamed peritoneum of BALB/c mice. These results indicate that nonanticoagulant sulfated saccharides targeted at P-selectin and L-selectin may have therapeutic potential in inflammatory disorders.

Developmentally regulated appearance of spliced variants of type XII collagen in the cornea.

PURPOSE: To determine whether temporal and spatial changes in the distribution of the long and short alternatively spliced variants of type XII collagen are associated with any specific morphogenetic events in pre- and postnatal development of the cornea and surrounding tissues. METHODS: The distribution of alternatively spliced variants of type XII collagen in fetal and newborn rabbit tissues was analyzed immunohistochemically using monoclonal antibodies that recognize either only the long form or both the short and the long forms of type XII collagen. RESULTS: During early fetal development of the cornea in rabbit (days 14 -17), the short form of type XII collagen was detected in the corneal stroma, the sclera, and the stroma in the rudimentary eyelid folds, whereas the long form was present only in the sclera. The long form was first evident in the cornea at day 24 but only in the posterior stroma. At later stages of prenatal development, the distribution of the long variant gradually extended toward the anterior stroma and in the newborn rabbit, the long variant was distributed throughout the entire stroma. However, in the eyelid, although the short form was present along the entire subepidermal regions both during fetal and neonatal development, the long form was transiently expressed between days 21 and 24 and was restricted to the subepidermal regions at the junction of the opposing eyelids. The long form of type XII collagen was first detectable in the basal epithelial cells and in its basement membrane (BM) at day 12 after birth, just before the opening of the eyelids. It continued to be present in the corneal BM zone in the adult rabbit but was not present in the limbal or conjunctival BM zone. CONCLUSIONS: The expression and distribution of the alternatively spliced forms of type XII collagen are developmentally and differentially regulated in the cornea, the sclera, and the eyelid. Although the short form is expressed in the stromal matrices of the cornea and surrounding tissues from early stages of corneal development, the appearance and distribution of the long variant form of type XII collagen coincide with the pattern of stromal condensation. Its first appearance in the corneal epithelial BM precedes the eyelid opening by 1 to 2 days, possibly suggesting that it may be involved in the tighter anchoring of the corneal epithelium to the underlying tissue or in promoting stromal condensation to assist in the separation of the corneal epithelium from the juxtaposed palpebral conjunctival epithelium of the eyelid.

Calpain III mutation analysis of a heterogeneous limb-girdle muscular dystrophy population.

OBJECTIVE: To determine the frequency of calpain III mutations in a heterogeneous limb-girdle muscular dystrophy (LGMD) population. BACKGROUND: Mutations of the calpain III gene have been shown to cause a subset of autosomal recessive LGMDs. Patient populations studied to date have been primarily of French and Spanish origin, in which calpain III may cause 30% of autosomal recessive MDs. The incidence of calpain III mutations in non-French/Spanish MD patients has not been studied thoroughly. No sensitive and specific biopsy screening methods for detecting patients with abnormal calpain III protein are available. Thus, detection of patients relies on direct detection of gene mutations. METHODS: The authors studied the calpain III gene in 107 MD patient muscle biopsies exhibiting normal dystrophin. Muscle biopsy RNA was produced for each patient, and the entire calpain III complementary DNA was screened for mutations by reverse-transcriptase PCR/single-strand conformation polymorphism using three different conditions. RESULTS: The authors identified nine patients (eight unrelated) with causative mutations. Six of the seven distinct mutations identified are novel mutations and have not been described previously. CONCLUSION: The results suggest that approximately 9.2% of patients in the heterogeneous population with an LGMD diagnosis will show mutations of the calpain III gene. Interestingly, two patients were heterozygous for a single mutation at the DNA level, whereas only the mutant allele was observed at the RNA level. This suggests that there are undetectable, nondeletion mutations that ablate expression of the calpain III gene.

Deaths among women of reproductive age in Cape Verde: causes and avoidability.

SUBJECT: In 1992-93 all deaths (n=97) of women 15 to 49 years old in three islands of Cape Verde were investigated to determine the cause of death, the maternal mortality ratio, the reliability of cause-of-death ascertainment, and the level of avoidability. METHOD: Data were obtained through interviews with the deceased person's family members and other knowledgeable persons (verbal autopsy) and through hospital files. RESULTS: The overall mortality rate was 163 per 100,000 women 1549 years old, and the maternal mortality ratio was 127 per 100,000 live births. A plausible diagnosis could be determined in 77%. The most frequent causes of death were circulatory disorders, external causes, maternal causes, infectious diseases. and neoplasms. CONCLUSIONS: It was estimated that three of four of the deaths were avoidable with locally available resources. Since access to health care in the study area is not a major hindrance, a further decrease of female mortality depends mainly on improved quality of care in health facilities.

Exercise studies in patients with transposition of the great arteries after atrial repair operations (Mustard/Senning): a review.

Exercise evaluation studies of patients after atrial repair surgery for transposition of the great arteries, as in tetralogy of Fallot, represent only a small fraction of the 3970 Medline references (1966 to mid-1997) concerning this congenital heart lesion. We have abstracted data from 27 studies from 20 institutions reporting on measurements during exercise on work capacity, heart rate response, respiratory gas exchange, or radionuclide/radiographic systemic ventricular ejection fraction measurements in addition to resting pulmonary function measurements. These studies provide almost uniform general conclusions that even after 20 or more years of follow-up (1) most patients "report" that they are asymptomatic in performing usual levels of physical activities; (2) significant abnormalities are present, often in more than half of the patients studied, in one or more of the exercise measurements when compared to control subjects; and (3) the diminished exercise performance is related to a diminished cardiac output, results from diminished stroke volume but is also related to a blunted heart rate response.

A Rho-associated protein kinase: differentially distributed in limbal and corneal epithelia.

PURPOSE: The authors have developed monoclonal antibodies (mAbs) to characterize the sequential biochemical changes in corneal epithelial cells after they differentiate from stem cells, located in the limbus, and migrate centripetally to follow the pathway of terminal differentiation. The purpose of this study was to identify a protein (recognized by mAb HE1/11F) with increased expression associated with the transition of the limbal epithelium to corneal epithelium. METHODS: The distribution and identification of the protein(s) were performed using an indirect immunohistochemical staining technique and a western blot analysis, respectively. A rabbit corneal epithelial cDNA library, constructed in the Uni-Zap XR vector, was screened with mAb HE1/11F to select cDNA clones expressing polypeptide(s) recognized by this mAb. Additional overlapping cDNA clones were obtained from a primer extension cDNA library to determine the sequence of the complete open reading frame encoding the protein recognized by mAb HE1/11F. RESULTS: Rabbit corneal epithelium exhibited strong immunostaining with mAb HE1/11F, however, the limbal epithelial cells stained weakly. HE1/11F recognized 160-kDa (HEBM1) and 100-kDa (HEBM2) polypeptides in the corneal epithelial extracts. The amino acid sequence of the protein deduced from the nucleotide sequence of the cDNA exhibited a close homology to that of a RhoA (Ras-related small GTPase)-associated serine-threonine kinase (ROCK-I or Rho-associated coiled-coil kinase). A 160-kDa RhoA-binding polypeptide with a molecular mass similar to that of HEBM1 and ROCK-I was detected in the corneal epithelial extracts. These findings strongly suggested that HEBM1 was rabbit ROCK-I. The identity of HEBM1 was further confirmed from the reactivity of mAb HE1/11F with ROCK-I immunoprecipitated from rabbit corneal epithelial extracts using anti-ROCK-I antibodies. CONCLUSIONS: The increased expression of a protein identified as ROCK-I from cDNA analyses is associated with rabbit corneal epithelial differentiation and transition from the limbal to corneal surface. Therefore, a RhoA signaling pathway is likely to be associated with corneal epithelial differentiation (maturation). A close homology among the cDNA sequences of rabbit, mouse, rat, and human ROCK-I indicates that this RhoA-associated kinase is a well-conserved protein.

Risk factors for perinatal death in Cape Verde.

Risk factors for perinatal death in the Cape Verde islands were assessed among 104 bereaved mothers and 292 mothers of surviving infants in an area-based case-control study in 1992-93. Prospectively gathered information on risk factors was obtained from medical records supplemented with post-partum interviews and anthropometric measurements of mothers and infants. No autopsies were performed. Multiple logistic regression analysis was applied. Out of 23 alleged maternal and two alleged infant risk factors, the following seven proved significantly and independently correlated with perinatal death: first pregnancy (odds ratio [OR] = 2.9); previous hypertensive disease (OR = 4.2); previous perinatal death (OR = 4.6); pre-eclampsia (OR = 7.0); non-cephalic fetal presentation (OR = 17.1); male infant (OR = 2.1) and maternal post-partum fever (OR = 3.1). The perinatal mortality rate was calculated as 37-46/1000 total births. A reduction in the mortality rate warrants antenatal and obstetric care with emphasis on primiparous women; improved detection and treatment of hypertensive disorders and genital infections; and improved intrapartum fetal observation and resuscitation routines.

PIP: Findings are presented from a study conducted to assess the perinatal mortality rate and explore the association between alleged maternal and pregnancy-related risk factors and perinatal death in Cape Verde. Risk factors for perinatal death were assessed among 104 bereaved mothers and 292 mothers of surviving infants in an area-based case-control study during 1992-93 using data on risk factors obtained from medical records, postpartum interviews, and anthropometric measurements of mothers and infants. The following alleged maternal and infant risk factors were significantly and independently correlated with perinatal death: first pregnancy, previous hypertensive disease, previous perinatal death, pre-eclampsia, noncephalic fetal presentation, male infant gender, and maternal postpartum fever. The perinatal mortality rate was calculated to be 37-46/1000 total births. Providing antenatal and obstetric care with emphasis upon primiparous women, improving the detection and treatment of hypertensive disorders and genital infections, and improving intrapartum fetal observation and resuscitation routines will help reduce the level of mortality.

Genital infections among antenatal care attendees in Cape Verde.

In a cross-sectional study, 350 pregnant Capeverdian women were examined to assess the prevalence of Chlamydia trachomatis infection (CT), Neisseria gonorrhoeae infection (NG) and Bacterial vaginosis (BV). Among various analytic methods used, the polymerase chain reaction PCR (for NG, CT) yielded a higher detection rate than did direct microscopy or culture (NG), or direct immuno-fluorescence (CT). Since the PCR analytic of air-dried specimens is not hampered by harsh storage and transport conditions, it could serve to validate other detection methods where laboratory facilities are suboptimal. Among sociodemographic risk factors young age, and currently living alone, were significantly associated with infection.

Type XII collagen contributes to diversities in human corneal and limbal extracellular matrices.

PURPOSE: To characterize diversities in the extracelhtlar matrices (ECMs) of the corneal and the surrounding limbal epithelium and stroma. METHODS: Immunohistochemical analyses were employed for screening monoclonal antibodies (mAbs) developed against ECM components of the human corneal epithelial basement membrane (BM) zone. In the current study, mAb BM8 was used as the monospecific probe to characterize its antigen (AgBM8) immunochemically, and to immunoselect a complementary DNA (cDNA) clone encoding AgBM8. Direct biochemical and cDNA sequence analyses were performed for the further characterization of AgBM8. An indirect colloidal gold-conjugated antibody technique was employed for immunoelectron microscopic analysis to study the distribution of AgBM8 in the corneal ECMs. RESULTS: The protein AgBM8, isolated from rabbit corneal stromal and epithelial tissues, was identified as the long-splice variant form of type XII collagen based on its size (approximately 340 kDa disulfide-linked subunits), the presence of collagenous domain(s) and a noncollagenous domain of approximately 300 kDa in its subunit structure, and its internal amino acid sequences. The identity of AgBM8 was further confirmed from the amino acid sequence (517 amino acids) deduced from the sequence of a cDNA immunoselected with mAb BM8. Immunofluorescence analyses indicated that the long form of type XII collagen is present in the ECMs of corneal stroma and in the sclera, as well as in the corneal epithelial BM zone but is absent in the limbal and conjunctival epithelial BM zones. It was not detectable in the subepithelial loose connective tissues in the limbus and in the bulbar conjunctiva. Immunoelectron microscopic analyses indicated that the long variant form of type XII collagen is present in corneal epithelial BM, Bowman's membrane, and the interfibrillar matrix of the corneal stroma. In the stroma, colloidal gold was distributed along the collagen fibrils with a periodicity of 150 to 200 nm. CONCLUSIONS: The long variant form of human type XII collagen, a member of the fibril-associated collagens with interrupted triple helices, referred to as FACITs, contributes to the differences in the BM zones of the cornea and limbus. Although many of the dense connective tissues in adult animals contain the short variant form of type XII collagen, human corneal stroma, the BM zone, and the sclera contain the long variant form as the predominant form of type XII collagen. In the corneal stroma, type XII collagen may be organized along the collagen fibrils in a uniform head-to-tail pattern.