Structure of the human Lanosterol synthase gene and its analysis as a candidate for holoprosencephaly (HPE1)

Holoprosencephaly (HPE) is the most common birth defect of the brain in humans. It involves various degrees of incomplete separation of the cerebrum into distinct left and right halves, and it is frequently accompanied by craniofacial anomalies. The HPE1 locus in human chromosome 21q22.3 is one of a dozen putative genetic loci implicated in causing HPE. Here, we report the complete gene structure of the human lanosterol synthase (LS) gene, which is located in this interval, and present its mutational analysis in HPE patients. We considered LS an excellent candidate HPE gene because of the requirement for cholesterol modification of the Sonic Hedgehog protein for the correct patterning activity of this HPE-associated protein. Despite extensive pedigree analysis of numerous polymorphisms, as well as complementation studies in yeast on one of the missense mutations, we find no evidence that the LS gene is in fact HPE1, implicating another gene located in this chromosomal region in HPE pathogenesis.

Transcranial magnetic stimulation of left temporoparietal cortex in three patients reporting hallucinated "voices"

BACKGROUND

Prior studies suggest that auditory hallucinations of "voices" arise from activation of speech perception areas of the cerebral cortex. Low frequency transcranial magnetic stimulation (TMS) can reduce cortical activation.

METHODS

We have studied three schizophrenic patients reporting persistent auditory hallucinations to determine if low frequency TMS could curtail these experiences. One hertz stimulation of left temporoparietal cortex was compared with sham stimulation using a double-blind, cross-over design.

RESULTS

All three patients demonstrated greater improvement in hallucination severity following active stimulation compared to sham stimulation. Two of the three patients reported near total cessation of hallucinations for > or = 2 weeks.

CONCLUSIONS

TMS may advance our understanding of the mechanism and treatment of auditory hallucinations.

Mutations in the homeodomain of the human SIX3 gene cause holoprosencephaly

Holoprosencephaly (HPE) is a common, severe malformation of the brain that involves separation of the central nervous system into left and right halves. Mild HPE can consist of signs such as a single central incisor, hypotelorism, microcephaly, or other craniofacial findings that can be present with or without associated brain malformations. The aetiology of HPE is extremely heterogeneous, with the proposed participation of a minimum of 12 HPE-associated genetic loci as well as the causal involvement of specific teratogens acting at the earliest stages of neurulation. The HPE2 locus was recently characterized as a 1-Mb interval on human chromosome 2p21 that contained a gene associated with HPE. A minimal critical region was defined by a set of six overlapping deletions and three clustered translocations in HPE patients. We describe here the isolation and characterization of the human homeobox-containing SIX3 gene from the HPE2 minimal critical region (MCR). We show that at least 2 of the HPE-associated translocation breakpoints in 2p21 are less than 200 kb from the 5' end of SIX3. Mutational analysis has identified four different mutations in the homeodomain of SIX3 that are predicted to interfere with transcriptional activation and are associated with HPE. We propose that SIX3 is the HPE2 gene, essential for the development of the anterior neural plate and eye in humans.

Analysis of the mutational spectrum of the FGFR2 gene in Pfeiffer syndrome

Pfeiffer syndrome (PS) is one of the classical craniosynostosis syndromes correlated with specific mutations in the human fibroblast growth factor receptor (FGFR) genes, FGFR1 and FGFR2. In this study, we set out to examine the exons in FGFR2 most commonly associated with mutations in PS, exons IIIa and IIIc, in a panel of 78 unrelated individuals with PS by the most sensitive method (direct DNA sequencing). We have identified a total of 18 different mutations among 40 patients; eight of these mutations have not been previously described. The mutational spectrum displays a non-random character with the frequent involvement of cysteine codons.

Opitz G/BBB syndrome in Xp22: mutations in the MID1 gene cluster in the carboxy-terminal domain

The MID1 gene in Xp22 codes for a novel member of proteins containing a RING finger, B-box, coiled-coil and a conserved C-terminal domain. Initially, three mutations in the C-terminal region were found in patients with Opitz G/BBB syndrome, a defect of midline development. Here we have determined the complete gene structure of the MID1 gene and have analyzed all nine exons for mutations in a set of 40 unrelated Opitz G/BBB patients. We now report six additional mutations all clustered in the carboxy-terminal domain of the MID1 protein. These data suggest that this conserved domain of the B-box proteins may play a fundamental role in the pathogenesis of Opitz syndrome and in morphogenetic events at the midline during blastogenesis.

Holoprosencephaly: a paradigm for the complex genetics of brain development

Holoprosencephaly (HPE) is the most common major developmental defect of the forebrain in humans. Clinical expression is variable, ranging from a small brain with a single cerebral ventricle and cyclopia to clinically unaffected carriers in familial HPE. Significant aetiological heterogeneity exists in HPE and includes both genetic and environmental causes. Recently, defects in the cell signalling pathway involving the Sonic Hedgehog (SHH) gene, as well as defects in the cholesterol biosynthesis, have been shown to cause HPE in humans. These discoveries and current genetic approaches serve as a paradigm for studying normal and abnormal brain morphogenesis.

Human developmental disorders and the Sonic hedgehog pathway

Sonic hedgehog (Shh) is a morphogen that is crucial for normal development of a variety of organ systems, including the brain and spinal cord, the eye, craniofacial structures, and the limbs. Mutations in the human SHH gene and genes that encode its downstream intracellular signaling pathway cause several clinical disorders. These include holoprosencephaly (HPE, the most common anomaly of the developing forebrain), nevoid basal cell carcinoma syndrome, sporadic tumors, including basal cell carcinomas, and three distinct congenital disorders: Greig syndrome Pallister-Hall syndrome, and isolated postaxial polydactyly. These conditions caused by abnormalities in the SHH pathway demonstrate the crucial role of SHH in complex developmental processes, and molecular analyses of these disorders provide insight into the normal function of the SHH pathway in human development.

Analysis of patients with craniosynostosis syndromes for a pro246Arg mutation of FGFR4

An identical amino acid substitution in fibroblast growth factor receptors (FGFR) 1, 2 and 3 occurs in patients with different craniosynostosis syndromes. We tested 113 patients with various craniosynostosis syndromes for the analogous Pro246Arg mutation in FGFR4 by a PCR-restriction enzyme assay. None of the patients displayed this change nor other mutations in the conserved linker region, as test by SSCP analysis. Mutations in this domain of FGFR4 are unlikely to contribute significantly to craniosynostosis in humans.

Analysis of the human Sonic Hedgehog coding and promoter regions in sacral agenesis, triphalangeal thumb, and mirror polydactyly

The human Sonic Hedgehog gene (SHH) is one of the vertebrate homologs related to the Drosophila segment polarity gene hedgehog. The entire coding and promoter region of the SHH gene, including 2 kb 5' of the transcriptional start site has been screened for mutations in families with autosomal dominant sacral agenesis and autosomal dominant triphalangeal thumb, two conditions previously known to be linked to 7q36. We have also studied the SHH gene in five families with mirror polydactyly associated with tibial hemimelia and in 51 unrelated patients with neural tube defects. Except for two sequence variants in exon 3, no mutations were found in these disease categories. OFF

Mutations in the C-terminal domain of Sonic Hedgehog cause holoprosencephaly

Holoprosencephaly (HPE) is the most common brain anomaly in humans, involving abnormal formation and septation of the developing central nervous system. Among the heterogeneous causes of HPE, mutations in the Sonic Hedgehog (SHH) gene have been shown to result in an autosomal dominant form of the disorder. Here we describe a total of five different mutations in the processing domain encoded by exon 3 of SHH in familial and sporadic HPE. This is the first instance in humans where SHH mutations in the domain responsible for autocatalytic cleavage and cholesterol modification of the N-terminal signaling domain of the protein have been observed.

Cytogenetic rearrangements involving the loss of the Sonic Hedgehog gene at 7q36 cause holoprosencephaly

Holoprosencephaly (HPE) is a genetically heterogeneous disorder that affects the midline development of the forebrain and midface in humans. As a step toward identifying one of the HPE genes, we have set out to refine the HPE3 critical region on human chromosome 7q36 by analyzing 34 cell lines from families with cytogenetic abnormalities involving 7q, 24 of which are associated with HPE. Genomic clones surrounding the DNA marker D7S104, which has previously been shown to be in the HPE3 critical region, have been examined by fluorescent in situ hybridization and microsatellite analysis of our panel of patient cell lines. We report the analysis of a cluster of four translocation breakpoints within a 300-kb region of 7q36 that serves to define the minimal critical region for HPE3 and that has directed the search for candidate genes. The human Sonic Hedgehog (hSHH) gene maps to this region and has been shown to be HPE3 on the basis of mutations within the coding region of the gene. We present evidence that cytogenetic deletions and/or rearrangements of this region of chromosome 7q containing Sonic Hedgehog, and translocations that may suppress Sonic Hedgehog gene expression through a position effect are common mechanisms leading to HPE.

Holoprosencephaly in RSH/Smith-Lemli-Opitz syndrome: does abnormal cholesterol metabolism affect the function of Sonic Hedgehog?

The RSH/Smith-Lemli-Opitz syndrome (RSH/SLOS) is an autosomal recessive malformation syndrome associated with increased levels of 7-dehydro-cholesterol (7-DHC) and a defect of cholesterol biosynthesis at the level of 3 beta-hydroxy-steroid-delta7-reductase (7-DHC reductase). Because rats exposed to inhibitors of 7-DHC reductase during development have a high frequency of holoprosencephaly (HPE) [Roux et al., 1979], we have undertaken a search for biochemical evidence of RSH/SLOS and other possible defects of sterol metabolism among patients with various forms of HPE. We describe 4 patients, one with semilobar HPE and three others with less complete forms of the HPE sequence, in whom we have made a biochemical diagnosis of RSH/SLOS. The clinical and biochemical spectrum of these and other patients with RSH/SLOS suggests a role of abnormal sterol metabolism in the pathogenesis of their malformations. The association of HPE and RSH/SLOS is discussed in light of the recent discoveries that mutations in the embryonic patterning gene, Sonic Hedgehog (SHH), can cause HPE in humans and that the sonic hedgehog protein product undergoes autoproteolysis to form a cholesterol-modified active product. These clinical, biochemical, and molecular studies suggest that HPE and other malformations in SLOS may be caused by incomplete or abnormal modification of the sonic hedgehog protein and, possible, other patterning proteins of the hedgehog class, a hypothesis testable in somatic cell systems.

Mutations in the human Sonic Hedgehog gene cause holoprosencephaly

Holoprosencephaly (HPE) is a common developmental defect of the forebrain and frequently the midface in humans, with both genetic and environmental causes. HPE has a prevalence of 1:250 during embryogenesis and 1:16,000 newborn infants, and involves incomplete development and septation of midline structures in the central nervous system (CNS) with a broad spectrum of clinical severity. Alobar HPE, the most severe form which is usually incompatible with postnatal life, involves complete failure of division of the forebrain into right and left hemispheres and is characteristically associated with facial anomalies including cyclopia, a primitive nasal structure (proboscis) and/or midfacial clefting. At the mild end of the spectrum, findings may include microcephaly, mild hypotelorism, single maxillary central incisor and other defects (Fig. 1). This phenotypic variability also occurs between affected members of the same family. The molecular basis underlying HPE is not known, although teratogens, non-random chromosomal anomalies and familial forms with autosomal dominant and recessive inheritance have been described. HPE3 on chromosome 7q36 is one of at least four different loci implicated in HPE. Here, we report the identification of human Sonic Hedgehog (SHH) as HPE3-the first known gene to cause HPE. Analyzing 30 autosomal dominant HPE (ADHPE) families, we found five families that segregate different heterozygous SHH mutations. Two of these mutations predict premature termination of the SHH protein, whereas the others alter highly conserved residues in the vicinity of the alpha-helix-1 motif or signal cleavage site.

Identification of Sonic hedgehog as a candidate gene responsible for holoprosencephaly

Holoprosencephaly (HPE) is a genetically and phenotypically heterogenous disorder involving the development of forebrain and midface, with an incidence of 1:16,000 live born and 1:250 induced abortions. This disorder is associated with several distinct facies and phenotypic variability: in the most extreme cases, anophthalmia or cyclopia is evident along with a congenital absence of the mature nose. The less severe form features facial dysmorphia characterized by ocular hypertelorism, defects of the upper lip and/or nose, and absence of the olfactory nerves or corpus callosum. Several intermediate phenotypes involving both the brain and face have been described. One of the gene loci, HPE3, maps to the terminal band of chromosome 7. We have performed extensive physical mapping studies and established a critical interval for HPE3, and subsequently identified the sonic hedgehog (SHH) gene as the prime candidate for the disorder. SHH lies within 15-250 kilobases (kb) of chromosomal rearrangements associated with HPE, suggesting that a 'position effect' has an important role in the aetiology of HPE. As detailed in the accompanying report, this role for SHH is confirmed by the detection of point mutations in hereditary HPE patients.

Radioimmunotherapy of interleukin-2R alpha-expressing adult T-cell leukemia with Yttrium-90-labeled anti-Tac

Adult T-cell leukemia (ATL) is a malignancy of mature lymphocytes caused by the retrovirus human T-cell lymphotropic virus-I. It is an aggressive leukemia with a median survival time of 9 months; no chemotherapy regimen appears successful in inducing long-term disease-free survival. The scientific basis of the present study is that ATL cells express high-affinity interleukin-2 receptors identified by the anti-Tac monoclonal antibody, whereas normal resting cells do not. To exploit this difference, we administered anti-Tac armed with Yttrium-90 (90Y) to 18 patients with ATL initially (first 9 patients) in a phase I dose-escalation trial and subsequently (second group of 9 patients) in a phase II trial involving a uniform 10-mCi dose of 90Y-labeled anti-Tac. Patients undergoing a remission were permitted to receive up to eight additional doses. At the 5- to 15-mCi doses used, 9 of 16 evaluable patients responded to 90Y anti-Tac with a partial (7 patients) or complete (2 patients) remission. The responses observed represent improved efficacy in terms of length of remission when compared with previous results with unmodified anti-Tac. Clinically meaningful (> or = grade 3) toxicity was largely limited to the hematopoietic system. In conclusion, radioimmunotherapy with 90Y anti-Tac directed toward the IL-2R expressed on ATL cells may provide a useful approach for treatment of this aggressive malignancy.

[Hypophosphatemic osteomalacia acquired after renal transplantation: a a cause of severe osteoporosis]

Renal osteodystrophy improves after renal transplantation but, after the procedure, other forms of bone disease emerge. We report a male patient that received a renal allograft four years before, who consulted for low back pain secondary to multiple vertebral compression fractures. The patient had good renal function, a parathormone independent hyperphosphaturia, normal 25-OH cholecalciferol, increased urinary hydroxyproline, decreased osteocalcin, reduced bone density and a bone biopsy revealing osteomalacia. The diagnosis of hypophosphatemic osteomalacia was reached and treatment with phosphates and ergocalciferol was started but, despite this, the patient suffered a new fracture two years later. Two mechanisms can produce hypophosphatemia after a renal transplantation: a parathormone excess due to the previous renal failure, that disappears during the first year after the transplantation or a derangement in renal phosphate transport that can be due to a generalized proximal tubule solute transport derangement (Fanconi syndrome), parathormone hypersensitivity or to an "idiopathic" hyperphosphaturia. Despite a good treatment, bone mass is not recovered and there is a high fracture risk. Mineral metabolism must be closely monitored after a renal allograft and its alterations must be quickly treated.

[Primary cerebral lymphoma following+ kidney transplant: a case report and review of the literature]

We report a 30 year old male, presenting eight years after receiving a kidney transplant with intracranial hypertension and two hyperdense masses detected in a brain CAT scan, whose histopathological study revealed a giant cell immunoblastic lymphoma. The patient was successfully treated with chemo and radiotherapy and after 18 months of follow up there is no evidence of tumoral relapse. Immunocompromised patients, specially transplant recipients, had a several fold higher incidence of malignant tumors, specially primary lymphomas of the central nervous system. These are generally of B type, are associated to Epstein Barr virus and have a high mortality. Cancer must be considered in the differential diagnosis of masses of uncertain origin in transplant recipients.

The interleukin (IL) 2 receptor beta chain is shared by IL-2 and a cytokine, provisionally designated IL-T, that stimulates T-cell proliferation and the induction of lymphokine-activated killer cells

Late-phase human T-cell lymphotropic virus I-associated adult T-cell leukemia cells express IL-2 receptors (IL-2R) but no longer produce IL-2. We have reported that the IL-2-independent adult T-cell leukemia line HuT-102 secretes a cytokine, provisionally designated IL-T, that stimulates T-cell proliferation and lymphokine-activated killer cell activity. Stimulation of proliferation of the cytokine-dependent human T-cell line Kit-225 mediated by HuT-102-conditioned medium or by 3200-fold-purified IL-T was not blocked by the addition of antibodies against IL-2 or IL-2R alpha subunit. However, IL-T-mediated stimulation of this human T-cell line was inhibited by addition of Mik-beta 1, an antibody that binds specifically to IL-2R beta subunit. In addition, the activation of large granular lymphocytes to lymphokine-activated killer cells mediated by IL-T-containing conditioned medium was not blocked by antibodies directed toward IL-2 or IL-2 alpha but was inhibited by an antibody to IL-2R beta, suggesting the requirement of this receptor subunit for IL-T action. This conclusion was confirmed using an IL-3-dependent murine myeloid precursor cell line, 32D, that expresses IL-2R alpha and IL-2R gamma, but not IL-2R beta. Neither IL-2 nor IL-T stimulated 32D cell proliferation. However, after transfection with the gene encoding human IL-2R beta, 32D beta cells proliferated on addition of either cytokine. The IL-T-mediated stimulation of 32D beta proliferation was inhibited by an anti-IL-2R beta antibody but not by an anti-IL-2 antibody. Thus, the IL-T-mediated stimulation of T-cell and lymphokine-activated killer cell activation requires the expression of the IL-2R beta subunit.

A lymphokine, provisionally designated interleukin T and produced by a human adult T-cell leukemia line, stimulates T-cell proliferation and the induction of lymphokine-activated killer cells

In early phases of human T-cell lymphotrophic virus I-induced adult T-cell leukemia (ATL), the malignant cell proliferation is associated with an autocrine process involving coordinate expression of interleukin (IL) 2 and its receptor. However, during late-phase ATL, leukemic cells no longer produce IL-2 yet continue to express high-affinity IL-2 receptors. During studies to define pathogenic mechanisms that underlie this IL-2-independent proliferation, we demonstrated that the ATL cell line HuT-102 secretes a lymphokine, provisionally designated IL-T, that stimulates T-cell proliferation and the induction of lymphokine-activated killer cells. Conditioned medium from HuT-102, when added to the IL-2-dependent CTLL-2 line, yielded a stimulation index of 230. Since CTLL-2 was purported to be IL-2-specific, we performed a number of studies to exclude IL-2 production by HuT-102. Stimulation of CTLL-2 cells by HuT-102-conditioned medium was not meaningfully inhibited by addition of an antiserum to IL-2. Furthermore, uninduced HuT-102 cells did not express mRNA encoding IL-2 as assessed by Northern blot analysis. No biological activity on CTLL-2 cells was mediated by purified IL-1, IL-3, IL-4, IL-5, IL-6, IL-7, IL-9, IL-10, IL-12, IL-13, or granulocyte/macrophage colony-stimulating factor, thus differentiating these factors from IL-T. Based on preliminary biochemical data, IL-T is a protein with a pI value of 4.5 and a molecular mass in SDS gels of 14 kDa. In addition to its action on CTLL-2 cells, 3200-fold-purified IL-T stimulated proliferation of the human cytokine-dependent T-cell line Kit-225. Furthermore, addition of IL-T enhanced cytotoxic activity of large granular lymphocytes (i.e., induced lymphokine-activated killer cells). Thus, IL-T is a lymphokine that plays a role in T-cell proliferation and induction of lymphokine-activated killer cells. Furthermore, IL-T may contribute to IL-2-independent proliferation of select ATL cells and lines.

Cooperative interactions between the interleukin 2 receptor alpha and beta chains alter the interleukin 2-binding affinity of the receptor subunits

The interleukin 2 (IL-2) receptor (IL-2R) is a multisubunit receptor that includes three major IL-2 binding subunits, the IL-2R alpha, beta, and gamma chains. We have detected and analyzed cooperative interactions between the IL-2R alpha and beta chains (IL-2R alpha and IL-2R beta, respectively) in COS cells transfected with cDNAs encoding the IL-2R alpha, the IL-2R beta, or both cDNAs. We demonstrated that IL-2 F42A, an analog that fails to bind to the isolated IL-2R alpha subunit and would be predicted by the hierarchical affinity-conversion model to have impaired binding to cells expressing both chains, instead readily binds to the IL-2R alpha/beta heterodimer in COS cells. Furthermore, this binding is abolished by the antibody HIEI that separates the two IL-2R subunits. The monoclonal antibodies anti-Tac and Mik-beta 1 directed at the IL-2-binding sites on IL-2R alpha and IL-2R beta, respectively, block ligand binding to the heterodimer. This binding pattern is inconsistent with the strict hierarchical affinity-conversion model that mandates an initial binding of IL-2 to IL-2R alpha followed by binding of the IL-2/IL-2R alpha complex to IL-2R beta. Instead, our results support an alternative model of preformed complexes of IL-2R beta with other IL-2R subunits. In this alternative model, IL-2R alpha and -beta exist in part as preformed complexes in which the affinity of IL-2R beta for IL-2 is altered by the proximity of IL-2R alpha, through mechanisms that do not require the prior binding of IL-2 to IL-2R alpha.

The interleukin-2 receptor: a target for monoclonal antibody treatment of human T-cell lymphotrophic virus I-induced adult T-cell leukemia

Adult T-cell leukemia (ATL) is a malignancy of mature lymphocytes caused by the retrovirus human T-cell lymphotrophic virus-I (HTLV-I). It is an aggressive leukemia with an overall mortality rate of 50% within 5 months; no conventional chemotherapy regimen appears successful in inducing long-term disease-free survival in ATL patients. However, ATL cells constitutively express high-affinity interleukin-2 receptors (IL-2Rs) identified by the anti-Tac monoclonal antibody, whereas normal resting cells do not. To exploit this difference in receptor expression, we administered anti-Tac intravenously (IV) to 19 patients with ATL. In general the patients did not suffer untoward reactions, and in 18 of 19 cases did not have a reduction in normal formed elements of the blood. Seven patients developed remissions that were mixed (1 patient), partial (4 patients), or complete (2 patients), with partial and complete remissions lasting from 9 weeks to more than 3 years as assessed by routine hematologic tests, immunofluorescence analysis, and molecular genetic analysis of T-cell receptor gene rearrangements and of HTLV-I proviral integration. Furthermore, remission was associated with a return to normal serum calcium levels and an improvement of liver function tests. Remission was also associated in some cases with an amelioration of the profound immunodeficiency state that characterizes ATL. Thus the use of a monoclonal antibody that blocks the interaction of IL-2 with its receptor expressed on ATL cells provides a rational approach for treatment of this aggressive malignancy.

Electrophysiological studies of color processing in human visual cortex

Electrophysiological recordings from human visual cortex were carried out with electrodes chronically implanted in 13 patients for localization of an epileptogenic focus. Visual evoked potentials (VEPs) elicited by red or blue checkerboard stimuli were recorded using an adaptation stimulus-test stimulus design in which color was the most salient feature. A "significant color effect," defined as a statistically significant effect of the adaptation stimulus on test stimulus VEPs evoked by the same or a different color, was determined for various cortical regions: medial lingual gyrus, 20%; lateral lingual gyrus, 38%; posterior fusiform gyrus, 50%; anterior fusiform gyrus, 0%; inferior temporal gyrus, 5%; occipital pole, 30%; lateral surface of non-visual cortex, 6%; inferior parietal and temporal cortex, 5%. The time course of the significant color effects suggests that wave length-selective neuronal activity occurs initially at the first stage of cortical processing in the medial lingual gyrus, followed by progressively later activation of the lateral lingual gyrus, the posterior fusiform gyrus, and the inferior temporal gyrus. In two patients, stimulation of the lateral lingual and fusiform gyri elicited color sensations in the contralateral half-field, whereas stimulation of the medial lingual and cuneate gyri evoked retinotopically appropriate quadrantic "shimmering" devoid of color. These results suggest that a region of inferior occipital cortex, primarily the posterior portion of the fusiform gyrus, is involved in color perception and may be homologous with area V4 in monkeys. There is also a region of dorsolateral surface cortex which exhibits a fairly high percentage of significant color effects and when stimulated may evoke sensations of color. This region may be the same as the dorsolateral region thought to be involved in selective attention to color.