LETM1, a novel gene encoding a putative EF-hand Ca(2+)-binding protein, flanks the Wolf-Hirschhorn syndrome (WHS) critical region and is deleted in most WHS patients.

Deletions within human chromosome 4p16.3 cause Wolf-Hirschhorn syndrome (WHS), which is characterized by severe mental and developmental defects. It is thought that haploinsufficiency of more than one gene contributes to the complex phenotype. We have cloned and characterized a novel gene (LETM1) that is deleted in nearly all WHS patients. LETM1 encodes a putative member of the EF-hand family of Ca(2+)-binding proteins. The protein contains two EF-hands, a transmembrane domain, a leucine zipper, and several coiled-coil domains. On the basis of its possible Ca(2+)-binding property and involvement in Ca(2+) signaling and/or homeostasis, we propose that haploinsufficiency of LETM1 may contribute to the neuromuscular features of WHS patients.     

A unique genomic sequence in the Wolf-Hirschhorn syndrome [WHS] region of humans is conserved in the great apes

The Wolf-Hirschhorn syndrome (WHS) is caused by a partial deletion in the short arm of chromosome 4 band 16.3 (4p16.3). A unique-sequence human DNA probe (39 kb) localized within this region has been used to search for sequence homology in the apes' equivalent chromosome 3 by FISH-technique. The WHS loci are conserved in higher primates at the expected position. Nevertheless, a control probe, which detects alphoid sequences of the pericentromeric region of humans, is diverged in chimpanzee, gorilla, and orangutan. The conservation of WHS loci and divergence of DNA alphoid sequences have further added to the controversy concerning human descent.     

Physical and developmental phenotype analyses in a boy with Wolf-Hirschhorn syndrome

Wolf-Hirschhorn syndrome (WHS) is a rare genetic condition with characteristic facial traits, organ malformations, functional impairment and developmental delay due to partial short arm monosomy of chromosome 4. Although several hundreds of cases have been published to date, a systematic collection of its clinical symptoms and anthropological traits is missing in the literature, and reports on abilities and needs of children with WHS are scanty. Results of detailed physical and developmental phenotype analyses in a 1 10/12-year-old boy with monosomy 4p15.2-pter are presented. Physical analyses were based on systematic data acquisition. They disclosed a total of 32 clinical symptoms and 46 anthropological traits. Developmental analyses were based on the child's interactive play in an environment structured according to Montessori principles. They disclosed a total of 44 abilities and a number of needs to be satisfied by the environment for the support of the child's psychic and intellectual growth. While the physical phenotype is important for the diagnostic process, the developmental phenotype is essential for parental counseling.     

Mild phenotype due to inverse duplication 4p16.3 - P15.3 including the Wolf-Hirschhorn critical region

Duplication of distal 4p results in a recognizable clinical phenotype. We report here on a 3 year old girl with a de novo inverse duplication of the chromosome segment 4p16.3-p15.3. The symptoms in this patient are milder than those of previously described patients with 4p duplication syndrome and include a deep hairline, deep-set eyes, short pug nose, full cheeks, simian crease, clinodactily of the fifth digit, no speech development and a moderate psychomotor retardation. Fluorescence in situ hybridization (FISH) using a chromosome 4 painting probe confirmed that the extra material is of chromosome 4 origin. Further analysis with the Wolf-Hirschhorn critical region probe demonstrated the duplication of this region. The lysosomal hydrolase alpha-L-iduronidase (IDUA) gene which is mutated in mucopolysaccaridosis type I (MPS I) and mapped to 4p16.3 might be responsible for some of the MPS like facial features. A phenotype-genotype correlation analysis in combination with literature review was undertaken to allow a further delineation of partial trisomy 4p syndromes.     

Kinetic analyses as a critical parameter in defining the side population (SP) phenotype

The side population (SP) phenotype has been reported as a method to identify hematopoietic stem cells in the bone marrow based upon differential staining with the fluorescent dye, Hoechst 33342. This technique has drawn great interest in the stem cell community, as it may provide a simple approach to the enrichment of progenitor cells from a variety of normal and malignant tissues. The frequency of these cells and their performance in functional assays has varied considerably within the literature. To investigate mechanisms that may contribute to the SP phenotype, we measured the fluorescence emission of Hoechst-stained bone marrow cells as a function of both time and dye concentration using a custom flow cytometer and data acquisition software. These measurements demonstrate that all nucleated cells within the bone marrow undergo an identical staining pattern at varying rates, even under conditions previously reported to abrogate the SP. Therefore, the SP phenotype is not unique to stem cells, but rather represents a transient feature of marrow cells exposed to Hoechst 33342 for varying amounts of time. We propose that heterogeneity of SP-defined populations may be a consequence of the rate at which differing cell populations accumulate Hoechst 33342. Further, we suggest that dye uptake kinetics will likely be an important factor for optimal use of Hoechst 33342 in isolating stem cells.     

Mapping of the epitope of monoclonal antibody 2B4 to the proline-rich region of human Huntingtin, a region critical for aggregation and toxicity

Huntington's disease is a neurodegenerative disease caused by a polyglutamine (polyQ) expansion in Huntingtin, which provokes aggregation of a proteolytic amino-terminal fragment of the affected protein encompassing the polyQ expansion. Accumulation of mutant Huntingtin somehow triggers cellular dysfunction and leads to a progressive degeneration of striatal neurons. Despite considerable efforts, the function of Huntingtin as well as the precise molecular mechanisms by which the expanded polyQ elicits cellular dysfunction remain unclear. In addition, no treatment is available to prevent, cure, or even slow down the progression of this devastating disorder. Antibodies are valuable tools to understand protein function and disease mechanisms. Here, we have identified the epitope recognized by the mAb 2B4, a broadly used antibody generated against the amino-terminal region of Huntingtin, which detects both aggregated and soluble Huntingtin. The 2B4 antibody specifically recognizes amino acids 50-64 of human Huntingtin but not the murine homologous region. Furthermore, the 2B4 epitope resides within the proline-rich region of Huntingtin, which is critical for polyQ aggregation and toxicity. These properties suggest that the 2B4 antibody might be useful in antibody-based therapeutic strategies.     

Molecular and cellular characterization of the Down syndrome critical region protein 2

Down syndrome (DS) is caused by trisomy for human chromosome 21 and is the most common genetic cause of mental retardation. The distal 10 Mb region of the long arm of the chromosome has been proposed to be associated with many of the abnormalities seen in DS. This region is often referred to as the Down syndrome critical region (DSCR). We report here the results of our analyses of the DSCR protein 2 (DSCR2). Results from transiently transfected COS-1 and HEK293 cells suggest that DSCR2 is synthesized as a 43 kDa precursor protein, from which the N-terminus is cleaved resulting in a polypeptide of 41 kDa. The polypeptide is modified by still uncharacterized co- or post-translational modifications increasing the predicted molecular weight of 32.8 kDa by about 10 kDa. Analyses of the only putative N-glycosylation site by in vitro mutagenesis excluded the possibility of the contribution of N-glycosylation to this increase in molecular weight. Further, the results of intracellular localization studies and membrane fractionation assays indicate that DSCR2 is targeted to a cytoplasmic compartment as a soluble form.     

DSCR2, a Down syndrome critical region protein, is localized to the endoplasmic reticulum of mammalian cells

We used immunocytochemical and fluorescence assays to investigate the subcellular location of the protein encoded by Down syndrome critical region gene 2 (DSCR2) in transfected cells. It was previously suggested that DSCR2 is located in the plasma membrane as an integral membrane protein. Interestingly, we observed this protein in the endoplasmic reticulum (ER) of cells. We also studied whether the truncated forms of DSCR2 showed different subcellular distributions. Our observations indicate that DSCR2 probably is not inserted into the membrane of the endoplasmic reticulum since the fragments lacking the predicted transmembrane (TM) helices remained associated with the ER. Our analyses suggest that, although DSCR2 is associated with the endoplasmic reticulum, it is not an integral membrane protein and it is maintained on the cytoplasmic side of the ER by indirect interaction with the ER membrane or with another protein.     

A molecular deletion of distal chromosome 4p in two families with a satellited chromosome 4 lacking the Wolf-Hirschhorn syndrome phenotype.

We report two families with a satellited chromosome 4 short arm (4ps). Satellites and stalks normally occur on the short arms of acrocentric chromosomes; however, the literature cites several reports of satellited nonacrocentric chromosomes, which presumably result from a translocation with an acrocentric chromosome. This is the first report of 4ps chromosomes. Our families are remarkable in that both unaffected and affected individuals carry the 4ps chromosome. The phenotypes observed in affected individuals, although dissimilar, were sufficient to encourage a search for a deletion of chromosome 4p. By Southern blot analysis and fluorescence in situ hybridization, a deletion of material mapping approximately 150 kb from chromosome 4pter was discovered. This deletion is notable because it does not result in the Wolf-Hirschhorn syndrome and can result in an apparently normal phenotype. We speculate that homology between subterminal repeat sequences on 4p and sequences on the acrocentric short arms may explain the origin of the rearrangement and that position effect may play a role in the expression of the abnormal phenotype.     

A new case of a severe clinical phenotype of the cat-eye syndrome

A new case of severe clinical phenotype of the cat-eye syndrome: We report on a female infant with severe clinical phenotype of Cat-Eye Syndrome (CES). At birth, she had respiratory distress and marked hypotonia. Physical examination showed major craniofacial anomalies including microcephaly, bilateral total absence of the external ears, hypertelorism, bilateral ocular coloboma of iris and micrognathia. In addition, she had anal stenosis, a patent ductus arteriosus and intra- and extra- hepatic biliary atresia. She deteriorated with the development of bradycardia. She died at age one month of cardiac failure. Cytogenetic analysis of the proband showed an extra de novo small bisatelllited marker chromosome in all cells examined. Molecular cytogenetic analysis with fluorescence in situ hybridization (FISH) identified the marker as a CES chromosome. Thus, the patient's karyotype was: 47, XX, +idic(22)(pter-->q11.2 ::q11.2-->pter). The duplication breakpoints giving rise to the CES chromosome were distal to the DiGeorge Syndrome (DGS) locus 22q11.2. The marker could be classed as a type 11 symmetrical (10). According to a recent review of CES literature (1) only 41 % of the CES patients have the combination of iris coloboma, anal anomalies and preauricular anomalies. Almost 60% are hard to recognize by their phenotype alone. Only twelve patients showed a severe clinical phenotype leading to the death of the child. This phenotypic variability increases the difficulties of genetic counseling.     

Mapping of a single locus capable of complementing the defective heterochromatin phenotype of Roberts syndrome cells

Roberts syndrome (RS) is a developmental disorder characterized by tetraphocomelia and a broad spectrum of additional clinical features. Most patients with RS exhibit characteristic cytogenetic phenotypes, which include an abnormal appearance of pericentromeric heterochromatin on metaphase chromosomes, referred to as "heterochromatic repulsion." In the present study, we use complementation of this abnormal cytogenetic phenotype as a means to identify a specific region of the normal human genome capable of rendering phenotypic correction. We screened the entire human genome, using a transient chromosome-transfer assay, and demonstrated complementation exclusively after the transfer of proximal chromosome 8p, a result subsequently confirmed by stable microcell-mediated chromosome transfer. Additionally, homozygosity mapping was used to refine the interval of this complementing locus to 8p21. The results are consistent with the notion that the single gene defect responsible for heterochromatic splaying and developmental abnormalities maps to chromosome 8p21.     

A new case of a syndrome including marfanoid phenotype and craniostenosis]

A new case of the syndrome with craniosynostosis and Marfanoid features is reported. The data presented and the analysis of relevant literature are suggestive of a community of the Marfanoid features with clinical and genetic heterogeneity. The possibility to delineate the Marfanoid syndrome with craniosynostosis as a nosologic unit and its etiology are discussed.     

Peg1/Mest locates distal to the currently defined imprinting region on mouse proximal chromosome 6 and identifies a new imprinting region affecting growth

Mice with maternal duplication for proximal chromosome 6 (Chr 6) die in utero before 11.5 dpc, an effect that can be attributed to genomic imprinting. Previous studies have defined the region of Chr 6 responsible as lying proximal to the T6Ad translocation breakpoint in G-band 6B3. Evidence presented here with a new Chr 6 translocation T77H has substantially reduced the size of the imprinting region, locating it between G-band 6A3.2 and the centromere. The paternally expressed imprinted gene Mest had been mapped within the original imprinting region and was therefore a candidate for the early embryonic lethality. FISH has shown that Mest locates distal to T77H and therefore outside the redefined imprinting region. This evidence confirms that Mest is not a candidate for the early embryonic lethality found with two maternal copies of proximal Chr 6. Furthermore mice with maternal duplication for Ch 6 distal to T77H (MatDp.dist6) were found to be growth retarded at birth, the weight reduction remaining similar until adulthood. It can be concluded that the growth retardation is established in utero and is maintained at a similar level from birth to adulthood. Therefore Mest locates in a new imprinting region, distal to G-band 6A3.2 which affects growth. A targeted mutation of Mest has been reported that exhibits growth retardation, reduced postnatal survival and abnormal maternal behaviour. Here the phenotype of MatDp.dist6 mice is compared to that of Mest-deficient mutant mice. Unlike the latter, MatDp.dist6 mice have good survival rates and females have normal maternal behaviour. Possible reasons for these differences are discussed.     

Investigation of a cryptic interstitial duplication involving the Prader-Willi/Angelman syndrome critical region

A 3-year-old female referred with developmental delay, hypotonia and seizures was found to have a cryptic interstitial duplication of the Prader-Willi/Angelman critical region (PWACR). Her clinical features form part of a common phenotype characteristic of PWACR duplications including developmental delay, behavioural problems and speech difficulties. Microsatellite analysis showed that the duplication had arisen de novo, was maternal in origin and involved the entire 4-Mb PWACR between the common deletion breakpoints. The existence of cryptic rearrangements emphasises the need for molecular tests alongside conventional cytogenetics when investigating abnormalities involving this imprinted region.     

Mapping of a gene for familial juvenile nephronophthisis: Refining the map and defining flanking markers on chromosome 2

Familial juvenile nephronophthisis (NPH) is an autosomal recessive kidney disease that leads to end-stage renal failure in adolescence and is associated with the formation of cysts at the cortico-medullary junction of the kidneys. NPH is responsible for about 15% of end-stage renal disease in children, as shown by Kleinknecht and Habib. NPH in combination with autosomal recessive retinitis pigmentosa is known as the Senior-Løken syndrome (SLS) and exhibits renal pathology that is identical to NPH. We had excluded 40% of the human genome from linkage with a disease locus for NPH or SLS when antignac et al. first demonstrated linkage for an NPH locus on chromosome 2. We present confirmation of linkage of an NPH locus to microsatellite markers on chromosome 2 in nine families with NPH. By linkage analysis with marker AFM262xb5 at locus D2S176, a maximum lod score of 5.05 at a θ_max = .03 was obtained. In a large NPH family that yielded at D2S176 a maximum lod score of 2.66 at θ_max = .0, markers AFM172xc3 and AFM016yc5, representing loci D2S135 and D2S110, respectively, were identified as flanking markers, thereby defining the interval for an NPH locus to a region of approximately 15 cM. Furthermore, the cytogenetic assignment of the NPH region was specified to 2p12-(2q13 or adjacent bands) by calculation of linkage between these flanking markers and markers with known unique cytogenetic assignment. The refined map may serve as a genetic framework for additional genetic and physical mapping of the region.     

Molecular definition of a region of chromosome 21 that causes features of the Down syndrome phenotype

Down syndrome (DS) is a major cause of mental retardation and heart disease. Although it is usually caused by the presence of an extra chromosome 21, a subset of the diagnostic features may be caused by the presence of only band 21q22. We now present evidence that significantly narrows the chromosomal region responsible for several of the phenotypic features of DS. We report a molecular and cytogenetic analysis of a three-generation family containing four individuals with clinical DS as manifested by the characteristic facial appearance, endocardial cushion defect, mental retardation, and probably dermatoglyphic changes. Autoradiograms of quantitative Southern blots of DNAs from two affected sisters, their carrier father, and a normal control were analyzed after hybridization with two to six unique DNA sequences regionally mapped on chromosome 21. These include cDNA probes for the genes for CuZn-superoxide dismutase (SOD1) mapping in 21q22.1 and for the amyloid precursor protein (APP) mapping in 21q11.2-21.05, in addition to six probes for single-copy sequences: D21S46 in 21q11.2-21.05, D21S47 and SF57 in 21q22.1-22.3, and D21S39, D21S42, and D21S43 in 21q22.3. All sequences located in 21q22.3 were present in three copies in the affected individuals, whereas those located proximal to this region were present in only two copies. In the carrier father, all DNA sequences were present in only two copies. Cytogenetic analysis of affected individuals employing R and G banding of prometaphase preparations combined with in situ hybridization revealed a translocation of the region from very distal 21q22.1 to 21qter to chromosome 4q. Except for a possible phenotypic contribution from the deletion of chromosome band 4q35, these data provide a molecular definition of the minimal region of chromosome 21 which, when duplicated, generates the facial features, heart defect, a component of the mental retardation, and probably several of the dermatoglyphic changes of DS. This region may include parts of bands 21q22.2 and 21q22.3, but it must exclude the genes S0D1 and APP and most of band 21q22.1, specifically the region defined by S0D1, SF57 and D21S47.