Exclusion mapping of the X-linked dominant chondrodysplasia punctata/ichthyosis/cataract/short stature (Happle) syndrome: possible involvement of an unstable pre-mutation

Confocal Microscopy Confirmed that in Phosphatidylcholine Giant Unilamellar Vesicles with very High Cholesterol Content Pure Cholesterol Bilayer Domains Form

The cholesterol (Chol) content in the fiber cell plasma membranes of the eye lens is extremely high, exceeding the solubility threshold in the lenses of old humans. This high Chol content forms pure Chol bilayer domains (CBDs) and Chol crystals in model membranes and membranes formed from the total lipid extracts from human lenses. CBDs have been detected using electron paramagnetic resonance (EPR) spin-labeling approaches. Here, we confirm the presence of CBDs in giant unilamellar vesicles prepared using the electroformation method from Chol/1-palmitoyl-2-oleoylphosphocholine and Chol/distearoylphosphatidylcholine mixtures. Confocal microscopy experiments using phospholipid (PL) analog (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine-5,5'-disulfonic acid) and cholesterol analog fluorescent probes (23-(dipyrrometheneboron difluoride)-24-norcholesterol) were performed, allowing us to make three major conclusions: (1) In all membranes with a Chol/PL mixing ratio (expressed as a molar ratio) >2, pure CBDs were formed within the bulk PL bilayer saturated with Chol. (2) CBDs were present as the pure Chol bilayer and not as separate patches of Chol monolayers in each leaflet of the PL bilayer. (3) CBDs, presented as single large domains, were always located at the top of giant unilamellar vesicles, independent of the change in sample orientation (right-side-up/upside-down). Results obtained with confocal microscopy and fluorescent Chol and PL analogs, combined with those obtained using EPR and spin-labeled Chol and PL analogs, contribute to the understanding of the organization of lipids in the fiber cell plasma membranes of the human eye lens.

Why Is Very High Cholesterol Content Beneficial for the Eye Lens but Negative for Other Organs?

The plasma membranes of the human lens fiber cell are overloaded with cholesterol that not only saturates the phospholipid bilayer of these membranes but also leads to the formation of pure cholesterol bilayer domains. Cholesterol level increases with age, and for older persons, it exceeds the cholesterol solubility threshold, leading to the formation of cholesterol crystals. All these changes occur in the normal lens without too much compromise to lens transparency. If the cholesterol content in the cell membranes of other organs increases to extent where cholesterol crystals forma, a pathological condition begins. In arterial cells, minute cholesterol crystals activate inflammasomes, induce inflammation, and cause atherosclerosis development. In this review, we will indicate possible factors that distinguish between beneficial and negative cholesterol action, limiting cholesterol actions to those performed through cholesterol in cell membranes and by cholesterol crystals.

Skin Barrier Function Is Not Impaired and Kallikrein 7 Gene Polymorphism Is Frequently Observed in Korean X-linked Ichthyosis Patients Diagnosed by Fluorescence in Situ Hybridization and Array Comparative Genomic Hybridization

X-linked ichthyosis (XLI) is a recessively inherited ichthyosis. Skin barrier function of XLI patients reported in Western countries presented minimally abnormal or normal. Here, we evaluated the skin barrier properties and a skin barrier-related gene mutation in 16 Korean XLI patients who were diagnosed by fluorescence in situ hybridization and array comparative genomic hybridization analysis. Skin barrier properties were measured, cytokine expression levels in the stratum corneum (SC) were evaluated with the tape stripped specimen from skin surface, and a genetic test was done on blood. XLI patients showed significantly lower SC hydration, but normal basal trans-epidermal water loss and skin surface pH as compared to a healthy control group. Histopathology of ichthyosis epidermis showed no acanthosis, and levels of the pro-inflammatory cytokines in the corneal layer did not differ between control and lesional/non-lesional skin of XLI patients. Among the mutations in filaggrin (FLG), kallikrein 7 (KLK7), and SPINK5 genes, the prevalence of KLK7 gene mutations was significantly higher in XLI patients (50%) than in controls (0%), whereas FLG and SPINK5 prevalence was comparable. Korean XLI patients exhibited unimpaired skin barrier function and frequent association with the KLK7 gene polymorphism, which may differentiate them from Western XLI patients.

Adult presentation of X-linked Conradi-Hünermann-Happle syndrome

Conradi-Hünermann-Happle syndrome, or X-linked dominant chondrodysplasia punctata type 2 (CDPX2), is a genodermatosis caused by mutations in EBP. While typically lethal in males, females with CDPX2 generally manifest by infancy or childhood with variable features including congenital ichthyosiform erythroderma, chondrodysplasia punctata, asymmetric shortening of the long bones, and cataracts. We present a 36-year-old female with short stature, rhizomelic and asymmetric limb shortening, severe scoliosis, a sectorial cataract, and no family history of CDPX2. Whole exome sequencing (WES) revealed a p.Arg63del mutation in EBP, and biochemical studies confirmed a diagnosis of CDPX2. Short stature in combination with ichthyosis or alopecia, cataracts, and limb shortening in an adult should prompt consideration of a diagnosis of CDPX2. As in many genetic syndromes, the hallmark features of CDPX2 in pediatric patients are not readily identifiable in adults. This demonstrates the utility of WES as a diagnostic tool in the evaluation of adults with genetic disorders.

Conradi-Hünermann-Happle syndrome in males vs. MEND syndrome (male EBP disorder with neurological defects)

BACKGROUND

There is confusion in the literature concerning disorders caused by EBP (emopamil-binding protein) mutations in males.

OBJECTIVES

To study the clinical and genetic differences in males affected either with Conradi-Hünermann-Happle (CHH) syndrome (X-linked dominant chondrodysplasia punctata, CDPX2) or with a nonmosaic, X-linked recessive disorder for which we propose the acronymic term MEND syndrome (male EBP disorder with neurological defects).

METHODS

We report a 7-year-old boy with a history of transient scaly erythematous lesions on his limbs, trunk and scalp soon after birth. DNA was isolated from ethylenediamine tetraacetic acid-blood samples of the patient and the four coding exons of the EBP gene were amplified by polymerase chain reaction. We review all published cases of CHH syndrome in males in the literature and elaborate the clinical and genetic differences between CHH syndrome in males and MEND syndrome.

RESULTS

We found at position 33 of the EBP gene the variant c.33C>A leading to the same nonsense mutation p.Y11X that had previously occurred de novo in a female with typical manifestations of CHH syndrome. When the known male cases with EBP mutations were reviewed, a striking nosological difference between the mosaic and nonmosaic phenotypes was evident. Clear-cut clinical criteria are elaborated to distinguish between CHH syndrome in males and MEND syndrome.

CONCLUSIONS

Because the clinical outcome and prognosis are different it is important to distinguish between males with CHH syndrome that represents a mosaic phenotype, and those with MEND syndrome that is a nonmosaic trait.

Specific entities affecting the craniocervical region: syndromes affecting the craniocervical junction

INTRODUCTION

The craniocervical junction is a vital component in understanding the function of the human central nervous system. It is the threshold for major pathways affecting both brain and spinal cord function, and these structures are intricately housed in a network of bone, ligaments, and soft tissues. Abnormal development of any of these components may lead to altered structure, and therefore, altered function in the central nervous system.

MATERIALS AND METHODS

We herein describe a set of genetic syndromes that commonly affect the craniovertebral junction and offer clinical examples from more than 6,000 patients who have been treated for these disorders.

DISCUSSION

The syndromes described include Chiari type I malformation, Conradi syndrome, Goldenhar syndrome, Klippel-Feil syndrome, Larsen syndrome, Morquio syndrome, Pierre-Robin syndrome, spondyloepiphyseal dysplasia congenital and Weaver syndrome. The genetic mechanisms responsible for these disorders may offer unique insight into the developmental pathways and patterning in the musculoskeletal and cranial systems and may, ultimately, guide future diagnosis and treatment.

Molecular cloning and characterization of a novel mouse actin-binding protein Zfp185

Zinc finger protein (Zfp) 185 is a mouse protein containing a Lin-l1, Isl-1 and Mec-3 (LIM) domains at its C-terminus. It was recognized by comparing the genome sequence between humans and mice in 1997. In this study, we cloned the full-length Zfp185 by means of RACE and RT-PCR. Zfp185 may be closely associated with F-actin in cells as determined by a confocal microscopy. With a series of deletants of Zfp185 and GST-pull-down assay, we determined that N-terminus region (1-144) but not the LIM domain at C-terminus of Zfp185 protein was essential and sufficient to bind to F-actin cytoskeleton. Thus, our data offered evidence for the association of mouse Zfp185 with F-actin, which supports the potential role of Zfp185 in cell fundamental activity.

Molecular prenatal diagnosis in a case of an X-linked dominant chondrodysplasia punctata

X-linked dominant chondrodysplasia punctata, (CDPX2-MIM302960) also known as Conradi-Hünermann-Happle syndrome, is a rare form of skeletal dysplasia that affects the skeleton, skin, hair, and eyes. The disorder is caused by mutations within the emopamil binding protein (Ebp) that functions as a delta(8), delta(7) sterol isomerase in the cholesterol biosynthesis pathway. To date, over 40 separate mutations have been reported in the Ebp gene, EBP, with no obvious correlation between the molecular defects and the severity of the clinical phenotype. We have studied a 30-year-old woman who presented in adulthood with skin, hair, and mild skeletal defects but no ocular abnormalities and have identified a heterozygous missense mutation within the third transmembrane domain of the protein. In addition, we have performed molecular prenatal testing on her unborn fetus. The results demonstrate inter-familial variability for missense mutations within the emopamil binding protein and add to the molecular data for CDPX2.

Characterization of mutations in 22 females with X-linked dominant chondrodysplasia punctata (Happle syndrome)

PURPOSE

Human X-linked dominant chondrodysplasia punctata (CDPX2) or Happle syndrome is associated with mutations in the human emopamil binding protein (EBP), a delta8-delta7-sterol isomerase involved in cholesterol biosynthesis. The purpose of the current study was to determine the spectrum of EBP mutations in females with CDPX2 and the utility of biochemical screening for the disorder by analysis of plasma sterols.

METHODS

Genomic sequencing of the coding exons of the human delta8-delta7-sterol isomerase gene was performed on DNA from 26 females with suspected X-linked dominant chondrodysplasia punctata. Clinical data and sterol analyses were obtained for 24 and 23 of the patients, respectively.

RESULTS

Mutations in the human EBP delta8-delta7-sterol isomerase gene were found in 22 (85%) of 26 females studied, including 20 (91%) of 22 patients who demonstrated an abnormal sterol profile. Thirteen of the mutations have not been reported previously. All of the females in whom mutations were found demonstrated typical skin manifestations of CDPX2, and all but one had a skeletal dysplasia.

CONCLUSIONS

Plasma sterol analysis was a highly specific and sensitive indicator of the presence of an EBP mutation in females with suspected CDPX2, including a clinically unaffected mother of a sporadic case. No clear genotype/phenotype correlations were ascertained, probably because phenotypic expression is influenced substantially by the pattern of X-inactivation in an affected female.

Gas chromatography-mass spectrometry and molecular genetic studies in families with the Conradi-Hünermann-Happle syndrome

The Conradi-Hünermann-Happle syndrome is an X-linked dominant disease that is due to mutations in the gene for emopamil binding protein. Emopamil binding protein is a Delta8-Delta7 sterol isomerase and plays a pivotal role in the final steps of cholesterol biosynthesis. We wanted to know to what extent this X-linked dominant enzyme defect has functional consequences at the biochemical level and whether it is possible to predict the clinical phenotype from serum sterol measurements. Therefore we performed sterol biochemical studies in 11 Conradi-Hünermann-Happle syndrome families and compared the results obtained to the clinical and molecular genetic findings. To assess disease severity a score considering bone and skin involvement and further features was used. For evaluation of the functional consequences we studied serum samples using gas chromatography-mass spectrometry analysis. For mutation screening we analyzed the emopamil binding protein gene using polymerase chain reaction, heteroduplex analysis of all exons, direct sequencing, and restriction enzyme analysis. Mutations in the emopamil binding protein gene were found in all 11 families including seven novel mutations affecting exons 2, 4, and 5. Gas chromatography-mass spectrometry analysis revealed markedly elevated levels of 8-dehydrocholesterol and of cholest-8(9)-en-3beta-ol and helped to identify somatic mosaicism in a clinically unaffected man. The extent of the metabolic alterations in the serum, however, do not allow prediction of the clinical phenotype, nor the genotype. This lack of correlation may be due to differences in X-inactivation between different tissues of the same patient and/or loss of the mutant clone by outgrowth of proficient clones after some time.

Inborn errors of sterol biosynthesis

The known disorders of cholesterol biosynthesis have expanded rapidly since the discovery that Smith-Lemli-Opitz syndrome is caused by a deficiency of 7-dehydrocholesterol. Each of the six now recognized sterol disorders-mevalonic aciduria, Smith-Lemli-Opitz syndrome, desmosterolosis, Conradi-Hünermann syndrome, CHILD syndrome, and Greenberg dysplasia-has added to our knowledge of the relationship between cholesterol metabolism and embryogenesis. One of the most important lessons learned from the study of these disorders is that abnormal cholesterol metabolism impairs the function of the hedgehog class of embryonic signaling proteins, which help execute the vertebrate body plan during the earliest weeks of gestation. The study of the enzymes and genes in these several syndromes has also expanded and better delineated an important class of enzymes and proteins with diverse structural functions and metabolic actions that include sterol biosynthesis, nuclear transcriptional signaling, regulation of meiosis, and even behavioral modulation.

Survival of male patients with incontinentia pigmenti carrying a lethal mutation can be explained by somatic mosaicism or Klinefelter syndrome

Incontinentia pigmenti (IP), or "Bloch-Sulzberger syndrome," is an X-linked dominant disorder characterized by abnormalities of skin, teeth, hair, and eyes; skewed X-inactivation; and recurrent miscarriages of male fetuses. IP results from mutations in the gene for NF-kappaB essential modulator (NEMO), with deletion of exons 4-10 of NEMO accounting for >80% of new mutations. Male fetuses inheriting this mutation and other "null" mutations of NEMO usually die in utero. Less deleterious mutations can result in survival of males subjects, but with ectodermal dysplasia and immunodeficiency. Male patients with skin, dental, and ocular abnormalities typical of those seen in female patients with IP (without immunodeficiency) are rare. We investigated four male patients with clinical hallmarks of IP. All four were found to carry the deletion normally associated with male lethality in utero. Survival in one patient is explained by a 47,XXY karyotype and skewed X inactivation. Three other patients possess a normal 46,XY karyotype. We demonstrate that these patients have both wild-type and deleted copies of the NEMO gene and are therefore mosaic for the common mutation. Therefore, the repeat-mediated rearrangement leading to the common deletion does not require meiotic division. Hypomorphic alleles, a 47,XXY karyotype, and somatic mosaicism therefore represent three mechanisms for survival of males carrying a NEMO mutation.

Novel and recurrent EBP mutations in X-linked dominant chondrodysplasia punctata

Chondrodysplasia punctata (CDP) is a heterogeneous group of skeletal dysplasias characterized by stippled epiphyses. A subtype of CDP, X-linked dominant chondrodysplasia punctata (CDPX2), known also as Conradi-Hünermann-Happle syndrome, is a rare skeletal dysplasia characterized by short stature, craniofacial defects, cataracts, ichthyosis, coarse hair, and alopecia. The cause of CDPX2 was unknown until recent identification of mutations in the gene encoding Delta(8),Delta(7) sterol isomerase emopamil-binding protein (EBP). Twelve different EBP mutations have been reported in 14 patients with CDPX2 or unclassified CDP, but with no evidence of correlation between phenotype and nature of the mutation. To characterize additional mutations and investigate possible phenotype-genotype correlation, we sequenced the entire EBP gene in 8 Japanese individuals with CDP; 5 of them presented with a CDPX2 phenotypes. We found EBP mutations in all 5 CDPX2 individuals, but none in non-CDPX2 individuals. Three of these CDPX2 individuals carried novel nonsense mutations in EBPand the other two, separate missense mutations that had been reported also in different ethnic groups. Our results, combined with previous information, suggest all EBP mutations that produce truncated proteins result in typical CDPX2, whereas the phenotypes resulted from missense mutations are not always typical for CDPX2. Patients with nonsense mutations showed abnormal sterol profiles consistent with a defect in Delta(8), Delta(7) sterol isomerase. X-inactivation patterns of the patients showed no skewing, an observation that supports the assumption that inactivation of the EBP gene occurs at random in affected individuals.

Functional X-chromosomal mosaicism of the skin: Rudolf Happle and the lines of Alfred Blaschko

In this article, the contribution of Rudolf Happle to the understanding of X-linked skin diseases is reviewed. In 1977 he proposed functional X-chromosomal mosaicism as the genetic mechanism underlying cutaneous anomalies that were seen in a number of X-linked skin diseases such as incontinentia pigmenti or focal dermal hypoplasia. Moreover, he recognized that these cutaneous anomalies followed the lines of Blaschko and thus he could tie in the development of the lines of Blaschko with a datable embryonic event. Convincing proof for the concept of functional X-chromosomal mosaicism was later provided by his group from functional sweat studies in female carriers of the X-linked gene defect hypohidrotic ectodermal dysplasia showing again on the back of the patient a gross, fountain-like mosaic typical of the lines of Blaschko. Moreover, in the years 1977 to 1981 he recognized the mosaic pattern in a syndrome of chondrodysplasia punctata, linear ichthyosis, patchy cicatricial alopecia, unilateral cataracts, and short stature again as a functional X-chromosomal mosaic becoming manifest exclusively in women and proposed that this syndrome, which is today named after him, is because of an X-linked dominant gene defect. Finally, the puzzling molecular genetics of the Happle syndrome are reviewed. Most likely, the Happle syndrome gene is not lethal for hemizygously affected males but rather similar to the example of epilepsy with mental retardation limited to females, the gene actually spares male gene carriers.

Mutations in a delta 8-delta 7 sterol isomerase in the tattered mouse and X-linked dominant chondrodysplasia punctata. jderry@immunex.com

Tattered (Td) is an X-linked, semi-dominant mouse mutation associated with prenatal male lethality. Heterozygous females are small and at 4-5 days of age develop patches of hyperkeratotic skin where no hair grows, resulting in a striping of the coat in adults. Craniofacial anomalies and twisted toes have also been observed in some affected females. A potential second allele of Td has also been described. The phenotype of Td is similar to that seen in heterozygous females with human X-linked dominant chondrodysplasia punctata (CDPX2, alternatively known as X-linked dominant Conradi-Hünermann-Happle syndrome) as well as another X-linked, semi-dominant mouse mutation, bare patches (Bpa). The Bpa gene has recently been identified and encodes a protein with homology to 3beta-hydroxysteroid dehydrogenases that functions in one of the later steps of cholesterol biosynthesis. CDPX2 patients display skin defects including linear or whorled atrophic and pigmentary lesions, striated hyperkeratosis, coarse lusterless hair and alopecia, cataracts and skeletal abnormalities including short stature, rhizomelic shortening of the limbs, epiphyseal stippling and craniofacial defects (MIM 302960). We have now identified the defect in Td mice as a single amino acid substitution in the delta8-delta7 sterol isomerase emopamil binding protein (Ebp; encoded by Ebp in mouse) and identified alterations in human EBP in seven unrelated CDPX2 patients.

X-linked dominant chondrodysplasia punctata: a peroxisomal disorder?

X-linked dominant chondrodysplasia punctata is characterised by resolving irregular punctate calcifications of epiphyses, variable ichthyosis and atrophoderma, short stature, and cataracts. We report on a patient with this syndrome who had transiently abnormal peroxisomal function tests. We review the literature and propose that X-linked dominant chondrodysplasia punctata is a peroxisomal disorder and that its phenotype can be explained by X chromosome lyonisation and the relative proliferation of cells expressing the normal X allele.

Genomic structure of a novel LIM domain gene (ZNF185) in Xq28 and comparisons with the orthologous murine transcript

Construction of a transcript map in the DXS52 region in Xq28 had previously led to the isolation of a cDNA with a LIM zinc finger domain in the carboxyl terminus. In parallel, the orthologous murine transcript was isolated from the syntenic region. The human and mouse cDNAs have been designated ZNF185 and Zfp185, respectively. By integrating the cDNA sequence with the cosmid-derived genomic sequence the exon-intron structure of the 3' end of the ZNF185 gene was resolved. Comparative sequence analyses of the human genomic sequence with the full-length murine cDNA facilitated prediction of the 5' end of the gene. The selective expression of three transcripts corresponding to the ZNF185 gene and a related gene was shown by Northern and Southern blots. In situ hybridizations revealed a nonubiquitous and stage-specific expression of Zfp185, especially in differentiating connective tissue. Since LIM proteins regulate cellular proliferation and/or differentiation by diverse mechanisms, and some have directly been associated with disease, conceivably ZNF185 may represent a candidate for a disease-causing gene linked to Xq28. Knowledge of the genomic structure will permit detailed mutation analyses.

Transcription mapping in a 700-kb region around the DXS52 locus in Xq28: isolation of six novel transcripts and a novel ATPase isoform (hPMCA5)

The chromosomal band Xq28 has been a focus of interest in human genetics because > 20 hereditary diseases have been mapped to this region. However, about two-thirds of the disease genes remain uncloned. The region around the polymorphic DXS52 locus (ST14) within Xq28 lies in the candidate regions for several as-yet-uncloned disease genes. So far, only four melanoma antigen genes (MAGE) and the human biglycan (BGN) gene, have been mapped within the 700-kb stretch around DXS52, suggesting that more genes may reside in this region. By combining exon trapping and direct cDNA selection methods, we sought to identify novel transcripts around the DXS52 locus. In addition to recovering the MAGE and BGN genes, we isolated and mapped six putative novel genes (XAP103-XAP108), the caltractin gene, and a gene encoding a novel Ca(2+)-transporting ATPase isoform (hPMCA5). The newly isolated sequences were considered as representing parts of putative genes if they contained at least one unique exon-trap product and/or at least one expressed sequence tag (EST) from sequence data bases and if, in addition, they showed evidence of expressed RT-OCT and/or Northern blot analysis. Our data facilitated the integration of the transcription map with the physical map around the DXS52 locus. Future analysis of the novel genes as candidates for Barth syndrome (BTHS) and chondrodysplasia punctata (CDPX2) is in progress.

A comparative transcription map of the murine bare patches (Bpa) and striated (Str) critical regions and human Xq28

The X-linked developmental mouse mutations bare patches (Bpa) and striated (Str) may be homologous to human X-linked dominant chondrodysplasia punctata (CDPX2) and incontinentia pigmenti (IP2), respectively, based on their genetic mapping and clinical phenotypes. Bpa and Str have been localized to an overlapping critical region of 600 kb that demonstrates conserved gene order with loci in human Xq28 between DXS1104 and DXS52. As part of efforts to isolate the genes involved in these disorders, we have begun to develop a comparative transcription map spanning this region in both species. Using techniques of cross-species conservation and hybridization, exon trapping, and cDNA selection we have identified four known genes or members of gene families--caltractin, a member of the gamma-aminobutyric acid (GABAA) receptor gene family, a member of the melanoma antigen gene (MAGE) family, and several members of the murine-specific, X-linked lymphocyte regulated gene (Xlr3) family. Trapped exons and, in some cases, longer cDNAs have been isolated for potentially 7-9 additional genes. One cDNA demonstrates highly significant homology with members of the Krüppel family of zinc finger transcription factors. A second novel cDNA demonstrates homology at the 3' end of the predicted amino acid sequence to a LIM domain consensus. Gene order appears conserved among those cDNAs determined to be present in both human and mouse. Three of the murine transcripts appear to be present in multiple copies within the Bpa/Str critical region and could be associated with a predisposition to genomic rearrangements. Reverse transcriptase PCR (RT-PCR) and Northern analysis demonstrate that several of the transcripts are expressed in mid-gestation murine embryos and neonatal skin, making them candidates for the Bpa and Str mutations and their respective homologous human disorders.

XXY male with X-linked dominant chondrodysplasia punctata (Happle syndrome)

Happle syndrome is an X-linked dominant disorder with presumed lethality in hemizygous males; familial occurrence is rare. We describe a family with Happle syndrome affecting individuals in 3 generations. A man in this family is the first known male patient with Happle syndrome. He is severely affected; this may be due to his 47,XXY karyotype.

The gene for Bazex-Dupré-Christol syndrome maps to chromosome Xq

Bazex-Dupré-Christol syndrome is an inherited condition with skin cancer predisposition characterized by follicular atrophoderma, hypotrichosis, and early onset of multiple basal cell carcinomas. Previous reports suggested an X-linked mode of inheritance. We therefore performed linkage analysis with microsatellite markers of the X chromosome in three families. We obtained evidence for X-linkage and regional assignment to Xq24-q27 of this syndrome (maximal lod score = 5.26 with a recombination fraction of 0% at the DXS1192 locus). This represents a first step towards the identification of a gene involved in hair follicle development and skin tumor formation.

Genetic mapping of the X-linked dominant mutations striated (Str) and bare patches (Bpa) to a 600-kb region of the mouse X chromosome: implications for mapping human disorders in Xq28

Striated (Str) and bare patches (Bpa) are X-irradiation-induced, X-linked dominant mouse mutations that are lethal prenatally in hemizygous males. To map the Str mutation, we generated a backcross involving Mus castaneus. Pedigree analysis of 193 affected female and normal male progeny from the cross places Str extremely close to DXMIT1 and favors a gene order of (Cf-9)-Ids-Gabra3-DXS1104h-(Str, DXMIT1)-F8a-DXPas8-DXBay6-DXMIT6 for the loci studied. This region of the mouse X Chromosome (Chr) is syntenic with proximal human Xq28. Based on the mode of inheritance and clinical phenotype, Str may be a homolog of human familial incontinentia pigmenti (IP2). Further refinement of our genetic mapping of bare patches positions that locus between DXS1104h and DXPas8 in the same region as Str, raising the possibility that Bpa and Str may be allelic or are due to mutations in overlapping contiguous genes.