Short-chain acyl-CoA dehydrogenase deficiency associated with early onset severe axonal neuropathy

Two unusual cases of axonal neuropathy associated with short-chain acyl-CoA dehydrogenase (SCAD) deficiency are described. These two unrelated infants presented with profound generalised weakness, particularly affecting the upper limbs. Clinical examination revealed generalised peripheral hypotonia and weakness, with absent deep tendon reflexes. An axonal polyneuropathy was confirmed on electromyogram (EMG) and nerve conduction studies (NCS) and, following an extensive metabolic screen, an acylcarnitine and organic acid profile consistent with a short-chain fatty acid beta-oxidation defect was found. In both cases, SCAD deficiency was confirmed by enzyme analysis. Genetic analysis showed the presence of common gene variations in the SCAD gene. SCAD deficiency is a rare disorder with a wide clinical phenotype. SCAD deficiency associated with axonal neuropathy has not previously been reported. As highlighted in these cases, it may be necessary to include axonal neuropathy as a presenting feature of SCAD.

Pilot trial of salbutamol in central core and multi-minicore diseases

Several studies have documented positive effects of beta-adrenergic agonists on human skeletal muscle with regard to muscle mass and strength. The aim of this pilot study was to evaluate the effect of the beta2-agonist salbutamol (albuterol) in a group of children with central core disease and multi-minicore disease. Thirteen patients, 8 with central core disease (mean age 17.5 years) and 5 with minicore disease (mean age 13.6 years) received oral salbutamol at a dose of 2 mg four times a day. Measures of efficacy were the change from baseline at 3 and 6 months in muscle strength, assessed by MRC score, myometry, functional measures and forced vital capacity. Statistical analysis was performed using repeated measures ANOVA (significance level < 0.05). Two patients with central core disease stopped the medication after one month because they did not notice any improvement and another one with minicore disease after 4 months because of increased tremors and palpitations. The remaining ten (6 with central core and 4 with minicore disease) completed the course of salbutamol without any significant adverse effects. There were significant increases in myometry, MRC scores and forced vital capacity between baseline and the six-month assessments. For both myometry and MRC the difference was already significant at 3 months and this was associated with a significant increase in functional abilities assessed with a structured functional scale. Our results suggest that salbutamol was overall well tolerated and might be beneficial in both central core and minicore patients. Larger prospective randomised, double-blind, placebo-controlled trials with salbutamol will be needed to confirm these preliminary findings.

Parathyroid hormone venous sampling prior to reoperation forprimary hyperparathyroidism

BACKGROUND

The surgical cure rate for primary hyperparathyroidismis greater than 95%. For those who have recurrent or persistent disease, preoperative localization improves reoperation success rates. Selective parathyroid venous sampling (SPVS) for intact parathyroid hormone is particularly useful when non-invasive localization techniques are negative or inconclusive.

METHODS

We present all known cases (n = 13)between 1994 and 2002 who had venous sampling for localization a tour institution prior to reoperation for recurrent or persistent primary hyperparathyroidism. Comparison was made with non-invasive localization procedures. Results of invasive and non-invasive localization were correlated with surgical findings.

RESULTS

Of the nine reoperated cases, eight had positive correlations between SPVS and operative findings and histopathology. SPVS did not reveal the parathyroid hormone source in one case with negative non-invasive localization procedures. Comparisons between SPVS,computerized tomography (CT), and parathyroid scintigraphy (MIBI)as expressed in terms of true positive (TP), false positive (FP)and false negative (FN) were: SPVS - TP88.8%, FP 0%, FN 11.1%; CT - TP22.2%, FP 22.2%, FN 55.5%; and MIBI - TP33.3%, FP 0%, FN 66.6%. At least seven of the nine operated cases have been cured; another remained normocalcaemic 2 weeks after subtotal parathyroidectomy.

CONCLUSION

In our institution SPVS has proven to be a valuable tool in cases with recurrent or persistent primary hyperparathyroidism and negative non-invasive localization procedures.

Occipito-temporal polymicrogyria and subclinical muscular dystrophy

We report a two-year-old Caucasian boy who had neonatal seizures and was found to have bilateral occipito-temporal polymicrogyria on neonatal brain MRI. The child had no additional neurological abnormality other than the neonatal seizures, but serum CK was found to be elevated (5 - 7 times normal values) and the muscle biopsy showed evidence of early muscular dystrophy. Detailed protein and genetic studies did not allow the identification of a known form of muscular dystrophy. The boy has been followed regularly and he currently has mild global developmental delay but no clinical signs of muscle involvement. The association of polymicrogyria and muscular dystrophy is known to occur in Fukuyama and Walker Warburg muscular dystrophies, in muscle-eye-brain disease and in some patients with merosin deficient CMD. However the absence of weakness and of eye involvement, the normal expression of merosin and alpha dystroglycan and the pattern of brain involvement make it very unlikely that the child is affected by one of these forms. As the pattern of brain involvement and the muscle pathology is not typical of one of the forms of neuronal migration disorders secondary to a known gene defect, we suspect that the combination of muscle and brain involvement found in this child is not coincidental. Our findings suggest that serum CK should be determined in children with undiagnosed polymicrogyria, even in the absence of weakness. This may lead to an expansion of our understanding of muscle dystrophies and cortical dysplasias.

Cloning of rat interleukin 11 and interleukin 11 receptor alpha chain and analysis of their expression in rat uterus in the peri-implantation period

Studies in mice have shown that interleukin 11 (IL-11) signalling is required for female fertility. In the absence of IL-11, decidualization is markedly retarded and implantation fails. IL-11 acts via a heterodimeric receptor composed of a ligand-specific receptor alpha chain (IL-11R alpha) and the signalling moiety gp130. This study reports the cloning of genes encoding rat IL-11 and IL-11R alpha. RNase protection was used to demonstrate that expression of IL-11 is upregulated in the rat uterus at the initiation of implantation at 5.5 days after mating. Expression of the genes encoding the two receptor components, IL11Ra and gp130, did not change throughout the peri-implantation period. In situ hybridization studies revealed that, as in mice, expression of IL-11 was high in the primary decidual zone at the time of the attachment reaction, whereas IL11Ra was expressed throughout primary and secondary decidua. Conservation of the temporal and spatial expression of IL-11 and IL-11R alpha in the uterus of the mouse and rat during the peri-implantation period will facilitate future studies investigating the role of IL-11 in fertility.

Placental defects and embryonic lethality in mice lacking suppressor of cytokine signaling 3

Mice lacking suppressor of cytokine signaling 3 (SOCS3) exhibited embryonic lethality with death occurring between days 11 and 13 of gestation. At this stage, SOCS3(-/-) embryos were slightly smaller than wild type but appeared otherwise normal, and histological analysis failed to detect any anatomical abnormalities responsible for the lethal phenotype. Rather, in all SOCS3(-/-) embryos examined, defects were evident in placental development that would account for their developmental arrest and death. The placental spongiotrophoblast layer was significantly reduced and accompanied by increased numbers of giant trophoblast cells. Delayed branching of the chorioallantois was evident, and, although embryonic blood vessels were present in the labyrinthine layer of SOCS3(-/-) placentas, the network of embryonic vessels and maternal sinuses was poorly developed. Yolk sac erythropoiesis was normal, and, although the SOCS3(-/-) fetal liver was small at day 12.5 of gestation (E12.5), normal frequencies of erythroblasts and hematopoietic progenitor cells, including blast forming unit-erythroid (BFU-E) and, colony forming unit-erythroid (CFU-E) were present at both E11.5 and E12.5. Colony formation for both BFU-E and CFU-E from SOCS3(-/-) mice displayed wild-type quantitative responsiveness to erythropoietin (EPO), in the presence or absence of IL-3 or stem cell factor (SCF). These data suggest that SOCS3 is required for placental development but dispensable for normal hematopoiesis in the mouse embryo.

Development and reorganization of corticospinal projections in EphA4 deficient mice

The Eph family of receptor tyrosine kinases and their ligands, the ephrins, are important regulators of axon guidance and cell migration in the developing nervous system. Inactivation of the EphA4 gene results in axon guidance defects of the corticospinal tract, a major descending motor pathway that originates in the cortex and terminates at all levels of the spinal cord. In this investigation, we report that although the initial development of the corticospinal projection is normal through the cortex, internal capsule, cerebral peduncle, and medulla in the brain of EphA4 deficient animals, corticospinal axons exhibit gross abnormalities when they enter the gray matter of the spinal cord. Notably, many corticospinal axons fail to remain confined to one side of the spinal cord during development and instead, aberrantly project across the midline, terminating ipsilateral to their cells of origin. Given the possible repulsive interactions between EphA4 and one of its ligands, ephrinB3, this defect could be consistent with a loss of responsiveness by corticospinal axons to ephrinB3 that is expressed at the spinal cord midline. Furthermore, we show that EphA4 deficient animals exhibit ventral displacement of the mature corticospinal termination pattern, suggesting that developing corticospinal axons, which may also express ephrinB3, fail to be repelled from areas of high EphA4 expression in the intermediate zone of the normal spinal cord. Taken together, these results suggest that the dual expression of EphA4 on corticospinal axons and also within the surrounding gray matter is very important for the correct development and termination of the corticospinal projection within the spinal cord.

Cloning, expression analysis, and chromosomal localization of murine and human homologues of a Xenopus mix gene

We report the cloning and chromosomal localization of murine and human Mix genes, members of a subclass of paired-like homeobox genes of which the Xenopus laevis Mix.1 gene is the founding member. The murine Mix gene was mapped to the distal region of chromosome 1 and the human region to the syntenic region 1q41-42. Northern analysis and RT-PCR of murine adult and embryonic tissues demonstrated that Mix expression was restricted to the early embryo. Whole-mount in situ hybridization revealed patchy but symmetrical Mix expression in visceral endoderm of embryonic day (E)5.5 embryos. In slightly older embryos, the expression was skewed to one side of the embryo and by E6.5, at the onset of gastrulation, expression was seen in the epiblast, visceral endoderm, nascent mesoderm, and the primitive streak. This expression pattern was maintained in mid- and late-streak embryos. In early bud-stage embryos, expression was strongest in the proximal two thirds of the streak, extending to the base of the allantois. By the headfold-stage, expression was confined to the remnant of the primitive streak in the caudal region of the embryo and, after E8.0, in the caudal notochord and tail bud mesoderm. Mix transcripts were no longer detectable after embryonic day 9.5.

Identification of somatic mutations of the MEN1 gene in sporadic endocrine tumours

Endocrine tumours of the pancreas, anterior pituitary or parathyroids arise either sporadically in the general population, or as a part of inherited syndromes such as multiple endocrine neoplasia type 1 (MEN 1). The mechanisms responsible for the development of sporadic endocrine lesions are not well understood, although loss of heterozygosity (LOH) of the MEN1 locus on chromosome 11q13 and somatic mutation of the MEN1 gene have been frequently associated with the development of MEN 1-type sporadic endocrine lesions. To further investigate the role of the MEN1 gene in sporadic endocrine tumorigenesis, we analysed DNA from 14 primary parathyroid lesions, 8 anterior pituitary tumours and 3 pancreatic tumours for the presence of somatic MEN1 gene mutations and LOH of seven microsatellite markers flanking the MEN1 locus. In addition, we similarly analysed 8 secondary parathyroid lesions which arose in patients with chronic renal failure. None of the patients studied had a family history of MEN 1. Three primary parathyroid lesions and one pancreatic tumour (glucagonoma) were found to have lost one allele at the MEN1 locus. Somatic mutations were identified by SSCP and sequence analysis in one of these parathyroid lesions (P320L) and in the glucagonoma (E179V). These results support previous findings that inactivation of the MEN1 tumour suppressor gene contributes to the development of sporadic MEN 1-type endocrine lesions but is not associated with the development of parathyroid hyperplasia seen in some renal failure patients.

The development of fatal myocarditis and polymyositis in mice heterozygous for IFN-gamma and lacking the SOCS-1 gene

Mice lacking the gene encoding the suppressor of cytokine signaling-1 (SOCS-1 -/-) and heterozygous for the IFN-gamma gene (IFN-gamma +/-) avoided the IFN-gamma-dependent preweaning death of SOCS-1 -/- IFN-gamma +/+ mice but did not exhibit the good health of young adult SOCS-1 -/- IFN-gamma -/- mice. SOCS-1 -/- IFN-gamma +/- mice died within 160 days of birth with massive T lymphocyte, macrophage, and eosinophil infiltration of all skeletal muscles and a similar severe myocarditis. The cornea also developed inflammatory infiltration and often a corneal ulcer. The mice exhibited evidence of selective CD8 T lymphocyte activation in populations in the thymus, spleen, and lymph nodes and focal T- and B-lymphoid infiltrates developed in the lung and salivary gland without apparent tissue damage. Comparison of SOCS-1 -/- IFN-gamma +/- mice with various control mice indicated that the development of tissue-damaging T lymphocyte, macrophage, and eosinophil infiltrates required loss of SOCS-1 and the presence of some IFN-gamma, but that the lung lymphoid infiltrates required only loss of SOCS-1 to develop.

Targeted insertion of a lacZ reporter gene into the mouse Cer1 locus reveals complex and dynamic expression during embryogenesis

The mouse Cer1 (mCer1, Cer-l, Cerr1) gene encodes one member of a family of cytokines structurally and functionally related to the Xenopus head-inducing factor, Cerberus (xCer). We generated a mouse line in which the Cer1 gene was inactivated by replacing the first coding exon with a lacZ reporter gene. Mice homozygous for this allele (Cer1(lacZ)) showed no apparent perturbation of embryogenesis or later development. However, the lacZ reporter revealed a number of hitherto uncharacterised sites of Cer1 expression in late fetal and adult tissues. Preliminary analysis suggests that Cer1 is not essential for their morphogenesis, differentiation, or homeostasis.

Structure-activity studies on gossypol in tumor cell lines

Gossypol [(2,2'-binaphthalene)-8,8'-dicarboxaldehyde-1,1',6,6',7,7'-hexahydroxy-5,5'-diisopropyl-3,3'-dimethyl] 1a is a naturally occurring compound extracted from the cotton plant and has been extensively studied as an oral male contraceptive. Its favorable toxicity profile, and the more recent demonstration of anti-tumor activity in animals and humans, prompted us to investigate the role of the aldehyde groups in a structure-activity study in cultured tumor cells. Four racemic compounds were evaluated: gossypol 1a, gossypolone 2, the bis Schiff's base of L-phenylalanine methyl ester with gossypol (bis Schiff's base) 1c and apogossypol 1b. The former two compounds both retain the aldehyde functional groups at positions 8 and 8' of the molecule whilst in the latter two compounds the aldehydes are blocked or absent, respectively. In addition, the l- and d-isomers of gossypol 1a, the bis Schiff's base 1c and the half Schiff's base 1d (one aldehyde blocked) were tested. The cell lines studied included melanoma (SK-mel-19), cervix (Sihas), small cell lung (H69) and myelogenous leukemia (K562). Cytotoxicity was measured using the MTT and flow cytometric viability assays. Racemic gossypol 1a and gossypolone 2 induced similar dose-dependent decreases in cell viability in all the cell lines with IC50 values of 23-46 and 28-50 microM, respectively. In contrast, the racemic bis Schiff's base derivative of gossypol 1c and apogossypol 1b showed minimal activity in any cell line up to 50 microM. The l-enantiomer of gossypol 1a was significantly more active than the d-enantiomer (IC50 of 20 versus > 50 microM, respectively). When one aldehyde of either enantiomer was blocked 1d cytoxicity was comparable to the l-enantiomer of gossypol. The data suggest that only one aldehyde group is required for the cytotoxicity of gossypol 1a, irrespective of the stereoconfiguration.

SCL expression in the mouse embryo detected with a targeted lacZ reporter gene demonstrates its localization to hematopoietic, vascular, and neural tissues

The helix-loop-helix transcription factor SCL (TAL1) is indispensable for blood cell formation in the mouse embryo. We have explored the localization and developmental potential of cells fated to express SCL during murine development using SCL-lacZ mutant mice in which the Escherichia coli lacZ reporter gene was 'knocked in' to the SCL locus. In addition to the hematopoietic defect associated with SCL deficiency, the yolk sac blood vessels in SCL(lacZ/lacZ) embryos formed an abnormal primary vascular plexus, which failed to undergo subsequent remodeling and formation of large branching vessels. Intraembryonic vasculogenesis in precirculation SCL(lacZ/lacZ) embryos appeared normal but, in embryos older than embryonic day (E) 8.5 to E9, absolute anemia leading to severe hypoxia precluded an accurate assessment of further vascular development. In heterozygous SCL(lacZ/w) embryos, lacZ was expressed in the central nervous system, vascular endothelia, and primitive and definitive hematopoietic cells in the blood, aortic wall, and fetal liver. Culture of fetal liver cells sorted for high and low levels of beta galactosidase activity from SCL(lacZ/w) heterozygous embryos indicated that there was a correlation between the level of SCL expression and the frequency of hematopoietic progenitor cells.

Suckling defect in mice lacking the soluble haemopoietin receptor NR6

Cytokines control a variety of cellular responses including proliferation, differentiation, survival and functional activation, via binding to specific receptors expressed on the surface of target cells [1]. The cytokine receptors of the haemopoietin family are defined by the presence of a conserved 200 amino acid extracellular domain known as the haemopoietin domain [2]. We report here the isolation of NR6, a haemopoietin receptor that, like the p40 subunit of interleukin-12 (IL-12) [3] and the EBI3 gene induced by Epstein-Barr virus infection in lymphocytes [4], contains a typical haemopoietin domain but lacks transmembrane and cytoplasmic domains. Although in situ hybridisation revealed NR6 expression at multiple sites in the developing embryo, mice lacking NR6 did not display obvious abnormalities and were born in the expected numbers. Neonatal NR6(-/-) mice failed to suckle, however, and died within 24 hours of birth, suggesting that NR6 is necessary for the recognition or processing of pheromonal signals or for the mechanics of suckling itself. In addition, NR6(-/-) mice had reduced numbers of haemopoietic progenitor cells, suggesting a potential role in the regulation of primitive haemopoiesis.

Stereo-specific cytotoxic effects of gossypol enantiomers and gossypolone in tumour cell lines

The naturally occurring compound, gossypol, has been previously used as a male oral contraceptive, for the treatment of benign gynaecological conditions and cancer patients. Long-term daily dosing with gossypol is associated with minimal side effects and no myelosuppression. Since gossypol exhibits atropisomerism due to the restricted rotation about the 2,2' carbon bond, we have isolated the l- and d-isomers by Schiff's base formation using a chiral amine and regenerated the enantiomers by acid hydrolysis. The enantiomers and the proposed oxidative metabolite, gossypolone, were characterized by HPLC, 1H-NMR and optical rotation. The cytotoxicity was assessed in cell cultures derived from melanoma, lung, breast, cervix, and leukaemia using the MTT viability assay. The cytotoxicity of gossypolone was similar to racemic gossypol in five out of the six cell lines studied. The l-enantiomer of gossypol induced a dose-dependent cell kill in all cell lines with a mean IC50 of 20 microM and was significantly more potent than racemic gossypol, the d-enantiomer of gossypol and gossypolone. In addition, when the leukaemia line was exposed to l-gossypol (0.5-10 microM) over a 4-day period, a schedule-dependent decrease in cell viability was observed. l-Gossypol was also compared with respective drugs used to treat patients with melanoma, lung cancer and leukaemia. The data indicate that l-gossypol was significantly more active than cisplatin, melphalan and dacarbazine in the two melanoma lines, cisplatin and daunorubicin in the lung line and hydroxyurea and busulphan in the leukaemia line. Preliminary studies using one melanoma line showed that the l-isomer induced cell shrinkage, membrane blebbing and DNA fragmentation, characteristics suggestive of apoptotic cell death.

EphA4 (Sek1) receptor tyrosine kinase is required for the development of the corticospinal tract

Members of the Eph family of tyrosine kinase receptors have been implicated in the regulation of developmental processes and, in particular, axon guidance in the developing nervous system. The function of the EphA4 (Sek1) receptor was explored through creation of a null mutant mouse. Mice with a null mutation in the EphA4 gene are viable and fertile but have a gross motor dysfunction, which is evidenced by a loss of coordination of limb movement and a resultant hopping, kangaroo-like gait. Consistent with the observed phenotype, anatomical studies and anterograde tracing experiments reveal major disruptions of the corticospinal tract within the medulla and spinal cord in the null mutant animals. These results demonstrate a critical role for EphA4 in establishing the corticospinal projection.

epicardin: A novel basic helix-loop-helix transcription factor gene expressed in epicardium, branchial arch myoblasts, and mesenchyme of developing lung, gut, kidney, and gonads

We report the cloning, chromosomal localization, and analysis of the expression pattern of epicardin, a member of the basic helix-loop-helix (bHLH) family of transcription factors. Within its bHLH domain, the human and murine epicardin genes were most similar to paraxis, a bHLH gene important for segmentation of embryonic paraxial mesoderm. In situ hybridization studies revealed strong epicardin expression in murine embryos at 9.5 days postcoitum (dpc) in a region of the septum transversum at the base of the heart known as the proepicardial organ. This mesenchymal structure extends villous projections from which epicardial precursor cells emerge and migrate out over the surface of the myocardium. Strong expression was seen in individual migratory cells and clusters at 9.5 dpc and in a continuous epicardial cell layer in more mature hearts. Also from 9.5 dpc, epicardin transcripts were seen in endocardial cushions of the atrioventricular canal and outflow tract, in skeletal myoblasts within branchial arches and in condensing mesenchyme of gut, kidney, urinary tract, gonads, spleen, and lung. Northern analysis showed that expression persisted in mature visceral organs and heart, but was transient in skeletal muscle. The central role played by bHLH factors in pathways for tissue determination in the embryo suggests a function for epicardin in specification of select mesodermal cell populations associated with heart, cranial skeletal muscle, gut, and urogenital system.

musculin: a murine basic helix-loop-helix transcription factor gene expressed in embryonic skeletal muscle

We describe the embryonic expression of musculin, a new murine member of the bHLH family of transcription factors. Musculin protein is closely related to human ABF-1, which is expressed in activated B cells, and to epicardin/capsulin/Pod-1, which is expressed in branchial myoblasts, visceral and urogenital mesoderm and epicardium. In situ hybridisation revealed musculin expression in embryos was largely restricted to the embryonic skeletal muscle lineage. While all skeletal muscles expressed the gene, only a subset of myocytes within each muscle were positive, indicating molecular heterogeneity within fetal muscle.

Infertility in female mice lacking the receptor for interleukin 11 is due to a defective uterine response to implantation

During early pregnancy, in response to the implanting embryo, the surrounding uterine stroma undergoes a dramatic transformation into a specialized tissue known as the decidua. The decidua encapsulates the developing embryo, facilitating nutrient transfer and limiting trophoblast invasion. Here we show that female mice with a null mutation of the interleukin-11 receptor alpha chain are infertile because of defective decidualization. A temporal analysis revealed IL-11 expression is maximal in the normal pregnant uterus at the time of decidualization, and in situ hybridization studies showed expression of the IL-11 and the IL-11 receptor alpha chain in the developing decidual cells. These observations reveal a previously unrecognized critical role for IL-11 signaling in female reproduction.

Clinicopathologic studies of thymic carcinoids in multiple endocrine neoplasia type 1

Thymic carcinoid is part of the multiple endocrine neoplasia type 1 (MEN1) syndrome occurring predominantly in male patients who were heavy smokers, presenting most commonly in middle age. In contrast with metastatic midgut carcinoids, MEN1-related thymic carcinoid is not associated with carcinoid syndrome, nor is it associated with Cushing syndrome, in contrast with sporadic thymic carcinoids. Local invasion and metastasis are common. Prognosis is poor because of late detection, lack of effective treatment, and the aggressive nature of the tumor. All patients with thymic carcinoids should be investigated for MEN1, including thorough clinical evaluation and family studies. Anterior mediastinal lesions in MEN1 male patients should be considered thymic carcinoids until proven otherwise. All male MEN1 patients and asymptomatic gene carriers should be warned of the risk of thymic carcinoids and the possible link to smoking. Computed tomography (CT) of the chest is recommended on first screening for MEN1 in male patients more than 25 years of age, followed by yearly chest X-rays and chest CT every 3 years. Prophylactic thymectomy should be carried out during subtotal or total parathyroidectomy on MEN1 patients.

Development of critical paths for post-acute brain injury rehabilitation: lessons learned

One important tool for case management is critical path analysis. This article explains four critical pathways developed by an interdisciplinary team for a post-acute brain injury rehabilitation program. The heterogeneity of the brain injury population mandates the need for systematic coordination of direct care services. Yet, variations in the neurobehavioral consequences of brain injury necessitate differing goals and treatment tracks for individual clients. The critical pathways in this setting define and describe the procedures and services to be rendered from admission to discharge to achieve optimal goals for four treatment program tracks: Return to Work, Return to School, Functional Independence, and Neurorehabilitation. The tracks reflect a hierarchy of expectations for information processing and functional performance. Critical pathways provide a tool for enhancing communication among service providers and external case managers and for determining the extent to which a client's course of treatment compares with a clinical standard considered to be ideal. This article compares the four critical pathways, provides representative case samples, and discusses lessons learned in the development and implementation process.