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

Malformation syndromes caused by disorders of cholesterol synthesis

Cholesterol homeostasis is critical for normal growth and development. In addition to being a major membrane lipid, cholesterol has multiple biological functions. These roles include being a precursor molecule for the synthesis of steroid hormones, neuroactive steroids, oxysterols, and bile acids. Cholesterol is also essential for the proper maturation and signaling of hedgehog proteins, and thus cholesterol is critical for embryonic development. After birth, most tissues can obtain cholesterol from either endogenous synthesis or exogenous dietary sources, but prior to birth, the human fetal tissues are dependent on endogenous synthesis. Due to the blood-brain barrier, brain tissue cannot utilize dietary or peripherally produced cholesterol. Generally, inborn errors of cholesterol synthesis lead to both a deficiency of cholesterol and increased levels of potentially bioactive or toxic precursor sterols. Over the past couple of decades, a number of human malformation syndromes have been shown to be due to inborn errors of cholesterol synthesis. Herein, we will review clinical and basic science aspects of Smith-Lemli-Opitz syndrome, desmosterolosis, lathosterolosis, HEM dysplasia, X-linked dominant chondrodysplasia punctata, Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects Syndrome, sterol-C-4 methyloxidase-like deficiency, and Antley-Bixler syndrome.

Hydroxysteroid (17beta) dehydrogenase 7 activity is essential for fetal de novo cholesterol synthesis and for neuroectodermal survival and cardiovascular differentiation in early mouse embryos

Hydroxysteroid (17beta) dehydrogenase 7 (HSD17B7) has been shown to catalyze the conversion of both estrone to estradiol (17-ketosteroid reductase activity) and zymosterone to zymosterol (3-ketosteroid reductase activity involved in cholesterol biosynthesis) in vitro. To define the metabolic role of the enzyme in vivo, we generated knockout mice deficient in the enzyme activity (HSD17B7KO). The data showed that the lack of HSD17B7 results in a blockage in the de novo cholesterol biosynthesis in mouse embryos in vivo, and HSD17BKO embryos die at embryonic day (E) 10.5. Analysis of neural structures revealed a defect in the development of hemispheres of the front brain with an increased apoptosis in the neuronal tissues. Morphological defects in the cardiovascular system were also observed from E9.5 onward. Mesodermal, endodermal, and hematopoietic cells were all detected by the histological analysis of the visceral yolk sac, whereas no organized vessels were observed in the knockout yolk sac. Immunohistological staining for platelet endothelial cell adhesion molecule-1 indicated that the complexity of the vasculature also was reduced in the HSD17B7KO embryos, particularly in the head capillary plexus and branchial arches. At E8.5-9.5, the heart development and the looping of the heart appeared to be normal in the HSD17B7KO embryos. However, at E10.5 the heart was dilated, and the thickness of the cardiac muscle and pericardium in the HSD17B7KO embryos was markedly reduced, and immunohistochemical staining for GATA-4 revealed that HSD17B7KO embryos had a reduced number of myocardial cells. The septum of the atrium was also defected in the knockout mice.

A Pex7 hypomorphic mouse model for plasmalogen deficiency affecting the lens and skeleton

Rhizomelic chondrodysplasia punctata type 1 is a peroxisome biogenesis disorder with the clinical features of rhizomelia, abnormal epiphyseal calcifications, congenital cataracts, and profound growth and developmental delays. It is a rare autosomal recessive disorder, caused by defects in the peroxisome receptor, PEX7. The pathology results from a deficiency of plasmalogens, a critical class of ether phospholipids whose functions are largely unknown. To study plasmalogens in an animal model, avoid early mortality and facilitate therapeutic investigations in this disease, we engineered a hypomorphic mouse model in which Pex7 transcript levels are reduced to less than 5% of wild type. These mice are born in expected ratios, are fertile and have a normal life span. However, they are petite and develop early cataracts. Further investigations showed delayed endochondral ossification and abnormalities in lens fibers. The biochemical features of reduced Pex7 function were reproduced in this model, including tissue plasmalogen deficiency, phytanic acid accumulation, reduced import of Pex7 ligands and consequent defects in plasmalogen biosynthesis and phytanic acid oxidation. Dietary supplementation with batyl alcohol, a plasmalogen precursor, recovered ether phospholipids in blood, but did not alter the clinical phenotype. The relatively mild phenotype of these mice mimics patients with milder PEX7 defects, and highlights the skeleton and lens as sensitive markers of plasmalogen deficiency. The role of plasmalogens in the normal function of these tissues at various ages can now be studied and additional therapeutic interventions tested in this model.

Chondrodysplasia punctata: a clinical diagnostic and radiological review

Chondrodysplasia punctata (CDP) is associated with a number of disorders, including inborn errors of metabolism, involving peroxisomal and cholesterol pathways, embryopathy and chromosomal abnormalities. Several classification systems of the different types of CDP have been suggested earlier. More recently, the biochemical and molecular basis of a number of CDP syndromes has recently been elucidated and a new aetiological classification has emerged. Here we provide an updated version with an overview of the different types of CDP, a discussion of the aetiology and a description of the clinical and radiographic findings. An investigative guideline to help determine the exact diagnosis in new cases is also presented.

Prenatal testing for a novel EBP missense mutation causing X-linked dominant chondrodysplasia punctata

OBJECTIVE

To determine the pathogenicity of a novel conserved missense mutation, p.Ser98Phe, in the emopamil binding protein (EBP) gene in order to perform a prenatal diagnostic test for X-linked dominant chondrodysplasia punctata (CDPX2) in a male foetus at 50% risk.

METHODS

Family members were tested for p.Ser98Phe using PCR and sequence analysis of leucocyte or buccal cell DNA. Haplotype analysis was employed to identify the grandparental chromosome on which p.Ser98Phe had arisen. In silico protein analyses were used to predict whether p.Ser98Phe significantly altered the EBP protein structure.

RESULTS

The mutation was detected in the proband and her affected mother but not in the maternal grandmother, who was thought to be mildly affected. However, haplotype analysis showed that p.Ser98Phe had arisen de novo on the grandpaternal X chromosome. Protein secondary structure predictions suggested that p.Ser98Phe alters the properties of the helix within which it is located.

CONCLUSION

We concluded that p.Ser98Phe is likely to be pathogenic and proceeded with prenatal testing. The male foetus had not inherited p.Ser98Phe and his unaffected status was confirmed at birth. This family demonstrates some of the difficulties in interpreting the significance of novel missense mutations, particularly when results are needed urgently for prenatal diagnosis.

Where does fetal and embryonic cholesterol originate and what does it do?

The development of a single-celled fertilized egg, through the blastocyst stage of a ball of cells and the embryonic stage when almost all organ systems begin to develop, and finally to the fetal stage where growth and physiological maturation occurs, is a complex and multifaceted process. A change in metabolism during gestation, especially when organogenesis occurs, can lead to abnormal development and congenital defects. Although many studies have described the roles of specific proteins in development, the roles of specific lipids, such as sterols, have not been studied as intensely. Sterol's functions in development range from being a structural component of membranes to regulating the patterning of the forebrain through sonic hedgehog to regulating expression of key proteins involved in metabolic processes. This review focuses on the roles of sterols in embryonic and fetal development and metabolism. Potential sources of cholesterol for the fetus and embryo are also discussed.

Disruption of the gene encoding 3beta-hydroxysterol Delta-reductase (Tm7sf2) in mice does not impair cholesterol biosynthesis

Tm7sf2 gene encodes 3beta-hydroxysterol Delta(14)-reductase (C14SR, DHCR14), an endoplasmic reticulum enzyme acting on Delta(14)-unsaturated sterol intermediates during the conversion of lanosterol to cholesterol. The C-terminal domain of lamin B receptor, a protein of the inner nuclear membrane mainly involved in heterochromatin organization, also possesses sterol Delta(14)-reductase activity. The subcellular localization suggests a primary role of C14SR in cholesterol biosynthesis. To investigate the role of C14SR and lamin B receptor as 3beta-hydroxysterol Delta(14)-reductases, Tm7sf2 knockout mice were generated and their biochemical characterization was performed. No Tm7sf2 mRNA was detected in the liver of knockout mice. Neither C14SR protein nor 3beta-hydroxysterol Delta(14)-reductase activity were detectable in liver microsomes of Tm7sf2((-/-)) mice, confirming the effectiveness of gene inactivation. C14SR protein and its enzymatic activity were about half of control levels in the liver of heterozygous mice. Normal cholesterol levels in liver membranes and in plasma indicated that, despite the lack of C14SR, Tm7sf2((-/-)) mice are able to perform cholesterol biosynthesis. Lamin B receptor 3beta-hydroxysterol Delta(14)-reductase activity determined in liver nuclei showed comparable values in wild-type and knockout mice. These results suggest that lamin B receptor, although residing in nuclear membranes, may contribute to cholesterol biosynthesis in Tm7sf2((-/-)) mice. Affymetrix microarray analysis of gene expression revealed that several genes involved in cell-cycle progression are downregulated in the liver of Tm7sf2((-/-)) mice, whereas genes involved in xenobiotic metabolism are upregulated.

Identification of essential amino acid residues in a sterol 8,7-isomerase from Zea mays reveals functional homology and diversity with the isomerases of animal and fungal origin

A putative 8,7SI (sterol 8,7-isomerase) from Zea mays, termed Zm8,7SI, has been isolated from an EST (expressed sequence tag) library and subcloned into the yeast erg2 mutant lacking 8,7SI activity. Zm8,7SI restored endogenous ergosterol synthesis. An in vitro enzymatic assay in the corresponding yeast microsomal extract indicated that the preferred Delta(8)-sterol substrate possesses a single C4alpha methyl group, in contrast with 8,7SIs from animals and fungi, thus reflecting the diversity in the structure of their active site in relation to the distinct sterol biosynthetic pathways. In accordance with the proposed catalytic mechanism, a series of lipophilic ammonium-ion-containing derivatives possessing a variety of structures and biological properties, potently inhibited the Zm8,7SI in vitro. To evaluate the importance of a series of conserved acidic and tryptophan residues which could be involved in the Zm8,7SI catalytic mechanism, 20 mutants of Zm8,7SI were constructed as well as a number of corresponding mutants of the Saccharomyces cerevisiae 8,7SI. The mutated isomerases were assayed in vivo by sterol analysis and quantification of Delta(5,7)-sterols and directly in vitro by examination of the activities of the recombinant Zm8,7SI mutants. These studies have identified His(74), Glu(78), Asp(107), Glu(121), Trp(66) and Trp(193) that are required for Zm8,7SI activity and show that binding of the enzyme-substrate complex is impaired in the mutant T124I. They underline the functional homology between the plant and animal 8,7SIs on one hand, in contrast with the yeast 8,7SI on the other hand, in accordance with their molecular diversity and distinct mechanisms.

Pathogenesis of permeability barrier abnormalities in the ichthyoses: inherited disorders of lipid metabolism

Many of the ichthyoses are associated with inherited disorders of lipid metabolism. These disorders have provided unique models to dissect physiologic processes in normal epidermis and the pathophysiology of more common scaling conditions. In most of these disorders, a permeability barrier abnormality "drives" pathophysiology through stimulation of epidermal hyperplasia. Among primary abnormalities of nonpolar lipid metabolism, triglyceride accumulation in neutral lipid storage disease as a result of a lipase mutation provokes a barrier abnormality via lamellar/nonlamellar phase separation within the extracellular matrix of the stratum corneum (SC). Similar mechanisms account for the barrier abnormalities (and subsequent ichthyosis) in inherited disorders of polar lipid metabolism. For example, in recessive X-linked ichthyosis (RXLI), cholesterol sulfate (CSO(4)) accumulation also produces a permeability barrier defect through lamellar/nonlamellar phase separation. However, in RXLI, the desquamation abnormality is in part attributable to the plurifunctional roles of CSO(4) as a regulator of both epidermal differentiation and corneodesmosome degradation. Phase separation also occurs in type II Gaucher disease (GD; from accumulation of glucosylceramides as a result of to beta-glucocerebrosidase deficiency). Finally, failure to assemble both lipids and desquamatory enzymes into nascent epidermal lamellar bodies (LBs) accounts for both the permeability barrier and desquamation abnormalities in Harlequin ichthyosis (HI). The barrier abnormality provokes the clinical phenotype in these disorders not only by stimulating epidermal proliferation, but also by inducing inflammation.

The etiopathogenesis of cleft lip and cleft palate: usefulness and caveats of mouse models

Cleft lip and cleft palate are frequent human congenital malformations with a complex multifactorial etiology. These orofacial clefts can occur as part of a syndrome involving multiple organs or as isolated clefts without other detectable defects. Both forms of clefting constitute a heavy burden to the affected individuals and their next of kin. Human and mouse facial traits are utterly dissimilar. However, embryonic development of the lip and palate are strikingly similar in both species, making the mouse a model of choice to study their normal and abnormal development. Human epidemiological and genetic studies are clearly important for understanding the etiology of lip and palate clefting. However, our current knowledge about the etiopathogenesis of these malformations has mainly been gathered throughout the years from mouse models, including those with mutagen-, teratogen- and targeted mutation-induced clefts as well as from mice with spontaneous clefts. This review provides a comprehensive description of the numerous mouse models for cleft lip and/or cleft palate. Despite a few weak points, these models have revealed a high order of molecular complexity as well as the stringent spatiotemporal regulations and interactions between key factors which govern the development of these orofacial structures.

A Botrytis cinerea emopamil binding domain protein, required for full virulence, belongs to a eukaryotic superfamily which has expanded in euascomycetes

A previous transcriptomic analysis of 3,032 fungal genes identified the Botrytis cinerea PIE3 (BcPIE3) gene to be up-regulated early in planta (A. Gioti, A. Simon, P. Le Pêcheur, C. Giraud, J. M. Pradier, M. Viaud, and C. Levis, J. Mol. Biol. 358:372-386, 2006). In the present study, BcPIE3 was disrupted in order to determine its implication in pathogenicity. BcPIE3 was shown to be a virulence factor, since the DeltaBcPIE3 mutant was blocked during the colonization of tomato and bean leaves, giving lesions reduced in size by at least 74%. Within the emopamil binding domain (EBD), BcPIE3 shows significant structural similarities to mammalian emopamil binding proteins (EBPs). Mammalian EBPs function as sterol isomerases, but an analysis of the sterol content and the results of growth inhibition experiments with the DeltaBcPIE3 strain indicated that BcPIE3 is dispensable for ergosterol biosynthesis. The systematic identification of EBD-containing proteins included in public databases showed that these proteins constitute a protein superfamily present only in eukaryotes. Phylogenetic analysis showed that the ancestral EBD-encoding gene was duplicated in the common ancestor of animals and fungi after the split from plants. Finally, we present evidence that the EBP phylogenetic clade of this superfamily has further expanded exclusively in euascomycetes, especially in B. cinerea, which contains three copies of the EBP gene.

Cervical spine stenosis in chondrodysplasia punctata

Chondrodysplasia punctata (CDP) is a rare skeletal dysplasia characterized by stippled epiphyses during infancy. The frequency is probably underdiagnosed because of the large heterogeneity in this group. Many genotypic variations exist. Although cervical instability is commonly seen in many skeletal dysplasias, cervical spine stenosis associated with CDP is very rare. We report a boy with phenotypic features of brachytelephalangic chondrodysplasia punctata (BCDP) who had severe cervical spine stenosis successfully corrected by vertebrectomies of C6 and C7 with a fibular strut graft. We discuss the significance of this association.

Novel EBP gene mutations in Conradi-Hünermann-Happle syndrome

BACKGROUND

Conradi-Hünermann-Happle syndrome [X-linked dominant chondrodysplasia punctata type 2 (CDPX2); MIM no. 302960] is an X-linked dominant disorder of cholesterol metabolism that causes a wide spectrum of skeletal abnormalities and linear ichthyosiform skin lesions. Mosaicism is probably responsible for the variability of the phenotype.

OBJECTIVES

To describe new mutations in patients with variable manifestations of the disease.

METHODS

We studied three patients with CDPX2. We performed mutation analysis of the EBP (formerly known as CDPX2) gene and gas chromatography-mass spectroscopy on serum of two patients.

RESULTS

We found two novel (3G-->T and 419-422delTTCT) and one known mutation in the EBP gene. We demonstrated the presence of increased levels of dehydrocholesterol and 8(9)-cholestenol in the two patients with new mutations, confirming the diagnosis of CDPX2 and strongly suggesting that the mutations are indeed pathogenic. One patient had a very mild phenotype, presenting with linear alopecia and a mild symmetrical epiphyseal dysplasia. X-inactivation studies in peripheral blood of all patients showed skewing in only the most severely affected patient.

CONCLUSIONS

The strong phenotypic variability in our patients suggests that there is no clear genotype-phenotype correlation.

Reduced penetrance in a family with X-linked dominant chondrodysplasia punctata

X-linked dominant chondrodysplasia punctata (Conradi-Hünermann disease, CDPX2) is characterised by short stature, stippled epiphyses, cataracts, ichthyosiform erythroderma and patchy alopecia of the scalp. The disorder is caused by mutations within the emopamil binding protein (EBP) gene encoding a 3beta-hydroxysteroid-Delta(8),Delta(7)-isomerase. The intrafamilial variation of disease severity is a known feature of CDPX2 probably caused by skewed X-inactivation. We report on a female fetus with typical symptoms of CDPX2 such as short limbs, postaxial polydactyly, ichthyotic skin lesions and punctate calcifications. Molecular genetic analysis of the EBP gene revealed a nonsense mutation (c.328C>T, p.R110X), which was previously detected in one CDPX2 patient and in a second female patient, who was only affected on one body side and erroneously diagnosed as CHILD syndrome. Surprisingly, the mother of our fetus carries the same mutation without having any signs of CDPX2. X-inactivation studies did not reveal any evidence of skewing neither in the mother nor in the fetus.

Mutations in X-linked PORCN, a putative regulator of Wnt signaling, cause focal dermal hypoplasia

Focal dermal hypoplasia is an X-linked dominant disorder characterized by patchy hypoplastic skin and digital, ocular and dental malformations. We used array comparative genomic hybridization to identify a 219-kb deletion in Xp11.23 in two affected females. We sequenced genes in this region and found heterozygous and mosaic mutations in PORCN in other affected females and males, respectively. PORCN encodes the human homolog of Drosophila melanogaster porcupine, an endoplasmic reticulum protein involved in secretion of Wnt proteins.

Deficiency of PORCN, a regulator of Wnt signaling, is associated with focal dermal hypoplasia

Focal dermal hypoplasia (FDH) is an X-linked dominant multisystem birth defect affecting tissues of ectodermal and mesodermal origin. Using a stepwise approach of (i) genetic mapping of FDH, (ii) high-resolution comparative genome hybridization to seek deletions in candidate chromosome areas and (iii) point mutation analysis in candidate genes, we identified PORCN, encoding a putative O-acyltransferase and potentially crucial for cellular export of Wnt signaling proteins, as the gene mutated in FDH. The findings implicate FDH as a developmental disorder caused by a deficiency in PORCN.

A severely affected female infant with x-linked dominant chondrodysplasia punctata: a case report and a brief review of the literature

We recently performed an autopsy on a premature female newborn with rhizomesoacromelic limb shortening of the upper and lower extremities, craniofacial dysmorphism, and chondrodysplasia punctata. A diagnosis of Conradi-Hunermann-Happle syndrome or X-linked dominant chondrodysplasia punctata was made based on elevated cholest-8(9)-ene-3beta-ol in serum and tissues. Molecular analysis of EBP, mutations of which are responsible for this malformation syndrome, revealed a monoallelic missense mutation, c.328 G>A (R110Q). We present this case as an illustration of an unusually severe manifestation of this disorder in a female, with additional unusual features including lack of skin manifestations and apparent bilateral symmetry of the skeletal findings.

Severe facial clefting in Insig-deficient mouse embryos caused by sterol accumulation and reversed by lovastatin

Insig-1 and Insig-2 are regulatory proteins that restrict the cholesterol biosynthetic pathway by preventing proteolytic activation of SREBPs and by enhancing degradation of HMG-CoA reductase. Here, we created Insig-double-knockout (Insig-DKO) mice that are homozygous for null mutations in Insig-1 and Insig-2. After 18.5 days of development, 96% of Insig-DKO embryos had defects in midline facial development, ranging from cleft palate (52%) to complete cleft face (44%). Middle and inner ear structures were abnormal, but teeth and skeletons were normal. The animals were lethargic and runted; they died within 1 day of birth. The livers and heads of Insig-DKO embryos overproduced sterols, causing a marked buildup of sterol intermediates. Treatment of pregnant mice with the HMG-CoA reductase inhibitor lovastatin reduced sterol synthesis in Insig-DKO embryos and reduced the pre-cholesterol intermediates. This treatment ameliorated the clefting syndrome so that 54% of Insig-DKO mice had normal faces, and only 7% had cleft faces. We conclude that buildup of pre-cholesterol sterol intermediates interferes with midline fusion of facial structures in mice. These findings have implications for the pathogenesis of the cleft palate component of Smith-Lemli-Opitz syndrome and other human malformation syndromes in which mutations in enzymes catalyzing steps in cholesterol biosynthesis produce a buildup of sterol intermediates.

Neuro(active)steroids actions at the neuromodulatory sigma1 (sigma1) receptor: biochemical and physiological evidences, consequences in neuroprotection

Steroids from peripheral sources or synthesized in the brain, i.e. neurosteroids, exert rapid modulations of neurotransmitter responses through specific interactions with membrane receptors, mainly the gamma-aminobutyric acid type A (GABA(A)) receptor and N-methyl-d-aspartate (NMDA) type of glutamate receptor. Progesterone and 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) act as inhibitory steroids while pregnenolone sulfate or dehydroepiandrosterone sulfate act as excitatory steroids. Some steroids also interact with an atypical protein, the sigma(1) (sigma(1)) receptor. This receptor has been cloned in several species and is centrally expressed in neurons and oligodendrocytes. Activation of the sigma(1) receptor modulates cellular Ca(2+) mobilization, particularly from endoplasmic reticulum pools, and contributes to the formation of lipid droplets, translocating towards the plasma membrane and contributing to the recomposition of lipid microdomains. The present review details the evidences showing that the sigma(1) receptor is a target for neurosteroids in physiological conditions. Analysis of the sigma(1) protein sequence confirmed homologies with the ERG2/emopamil binding protein family but also with the steroidogenic enzymes isopentenyl diphosphate isomerase and 17beta-estradiol dehydrogenase. Biochemical and physiological arguments for an interaction of neuro(active)steroids with the sigma(1) receptor are analyzed and the impact on physiopathological outcomes in neuroprotection is illustrated.

Defects of cholesterol biosynthesis

Eight distinct inherited disorders have been linked to different enzyme defects in the isoprenoid/cholesterol biosynthetic pathway following the finding of abnormally increased levels of intermediate metabolites in patients and confirmed by the demonstration of disease-causing mutations in genes encoding the implicated enzymes. Patients afflicted with these disorders are characterized by multiple morphogenic and congenital anomalies including internal organ, skeletal and/or skin abnormalities underlining an important role for cholesterol in human embryogenesis and development. The etiology of the underlying pathophysiology may involve multiple affected processes due to lowered cholesterol and/or the elevated, teratogenic levels of the intermediate sterol precursors.

Cataracts, ataxia, short stature, and mental retardation in a Chinese family mapped to Xpter-q13.1

Six males in a Chinese family affected by congenital cataracts, cerebellar ataxia, short stature, and mental retardation, which were tentatively named CASM syndrome. Eight female carriers in the family had cataracts alone. Linkage analysis demonstrated that the disease is transmitted through X-linked inheritance, either by setting the syndrome in males as an X-linked recessive trait, or by setting cataracts in the family as an X-linked dominant trait. The gene responsible for the syndrome is mapped to Xpter-Xq13.1, with the highest lod score of 3.91 for DXS1226, DXS991, and DXS1213 at theta = 0. Haplotype analysis identified that the allele harboring the disease gene co-segregated with all female carriers as well as affected males in the family. Clinically and genetically, the disease in this family is different from any known disease. Major features of CASM syndrome that distinguish it from other diseases are X-linked inheritance and cataracts in carrier females.

X-inactivation and human disease: X-linked dominant male-lethal disorders

X chromosome inactivation (XCI) is the process by which the dosage imbalance of X-linked genes between XX females and XY males is functionally equalized. XCI modulates the phenotype of females carrying mutations in X-linked genes, as observed in X-linked dominant male-lethal disorders such as oral-facial-digital type I (OFDI) and microphthalmia with linear skin-defects syndromes. The remarkable degree of heterogeneity in the XCI pattern among female individuals, as revealed by the recently reported XCI profile of the human X chromosome, could account for the phenotypic variability observed in these diseases. Furthermore, the recent characterization of a murine model for OFDI shows how interspecies differences in the XCI pattern between Homo sapiens and Mus musculus result in discrepancies between the phenotypes observed in patients and mice.

X-Linked dominant chondrodysplasia punctata: prenatal diagnosis and autopsy findings

OBJECTIVE

To report our experience of the prenatal diagnosis of X-linked dominant chondrodysplasia punctata (CDPX2) and highlight its variable phenotypic presentation.

METHODS

We report the sonographic features of three female fetuses affected with CDPX2. The ultrasound, radiographic and pathological findings were compared.

RESULTS

Family 1: Two affected pregnancies, both terminated. Fetus 1: Presented with epiphyseal stippling involving the vertebrae, upper and lower limbs, asymmetric shortening of the long bones and flat facial profile. Fetus 2: Prenatal findings included premature epiphyseal stippling, paravertebral cartilaginous calcific foci, mild shortening of the long bones and flat facies. Mutation analysis of the mother and both fetuses revealed mutation in the emopamil-binding protein (EBP) gene. Family 2: Prenatal sonography showed scattered epiphyseal stippling, minimal vertebral segmentation anomalies, mild asymmetric limb shortening and flat facies. Female infant delivered at 39 weeks of gestation. Biochemical analysis in all three fetuses showed increased levels of serum 8(9)-cholestenol consistent with delta (8), delta (7)-isomerase deficiency and CDPX2.

CONCLUSION

Prenatal diagnosis of CDPX2 is difficult because of marked phenotypic variation. Epiphyseal stippling, ectopic paravertebral calcifications, asymmetric shortening of long bones and dysmorphic flattened facies are crucial for prenatal diagnosis. DNA analysis of the CDPX2 gene and biochemical determination of the serum 8(9)-cholestenol level are important for diagnosis, especially if future pregnancies are planned.

Recent insights into the Smith-Lemli-Opitz syndrome

Recent insights into the Smith-Lemli-Opitz syndrome. The Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive multiple congenital anomaly/mental retardation disorder caused by an inborn error of post-squalene cholesterol biosynthesis. Deficient cholesterol synthesis in SLOS is caused by inherited mutations of 3beta-hydroxysterol-Delta7 reductase gene (DHCR7). DHCR7 deficiency impairs both cholesterol and desmosterol production, resulting in elevated 7DHC/8DHC levels, typically decreased cholesterol levels and, importantly, developmental dysmorphology. The discovery of SLOS has led to new questions regarding the role of the cholesterol biosynthesis pathway in human development. To date, a total of 121 different mutations have been identified in over 250 patients with SLOS who represent a continuum of clinical severity. Two genetic mouse models have been generated which recapitulate some of the developmental abnormalities of SLOS and have been useful in elucidating the pathogenesis. This mini review summarizes the recent insights into SLOS genetics, pathophysiology and potential therapeutic approaches for the treatment of SLOS.

CHILD syndrome caused by a deletion of exons 6-8 of the NSDHL gene

The X-linked dominant CHILD syndrome (congenital hemidysplasia with ichthyosiform nevus and limb defects) is a rare developmental defect characterized by a strictly lateralized inflammatory nevus. In the majority of cases, the right side of the body is affected. Ipsilateral hypoplastic lesions may involve the brain, skeletal structures, lungs, heart or kidneys. We describe a case of CHILD syndrome involving the left side of the body. Absence of metacarpal, metatarsal and phalangeal bones of the left hand and foot resulted in oligodactyly, with only 3 fingers and 1 toe. An ipsilateral inflammatory epidermal nevus with hyperkeratosis, parakeratosis, acanthosis and perivascular lymphohistiocytic infiltrate was strictly confined to the left half of the patient's body. The phenotype was shown to be associated with a deletion of exons 6-8 of the X-linked NSDHL gene, confirming that CHILD syndrome is due to loss of function of an enzyme involved in cholesterol biosynthesis.

Maternal cholesterol in fetal development: transport of cholesterol from the maternal to the fetal circulation

Cholesterol is required for fetal development. Data obtained from recent studies in humans, rodents, and cell cultures showed that circulating maternal cholesterol can affect fetal metabolism and sterol accretion. Recent studies in our laboratory showed that the efflux of cholesterol from the basolateral side of the placental cells and the secretion of cholesterol from endodermal yolk sac cells to the fetal circulation can be regulated. The ability to manipulate the mass of maternal cholesterol that crosses to the fetus could result in a dramatic improvement in the development of fetuses that lack the ability to synthesize cholesterol, such as those with Smith-Lemli-Opitz syndrome. On the other hand, it could also accelerate the development of various age-related diseases, such as atherosclerosis.

The expression of the 27-kd heat shock protein in keratinization disorders: an immunohistological study

In human skin, the 27-kd heat shock protein (hsp27), a member of the small hsp family, is expressed mainly in the upper epidermal layers. Hsp27 functions as a molecular chaperone and is involved in the regulation of cell growth and differentiation. According to experimental evidence, epidermal hsp27, through its chaperone function, might play a role in the assembly of keratin filaments and the cornified cell envelope. This study was conducted to assess the expression pattern of hsp27 in a panel of different ichthyoses. Twelve hereditary and acquired skin diseases associated with an ichthyotic phenotype and 2 corresponding mouse models were investigated by immunohistochemistry on formalin-fixed paraffin-embedded tissue, using a monoclonal antibody specific for hsp27. In ichthyosis vulgaris, lamellar ichthyosis, Sjögren-Larsson syndrome, Netherton syndrome, and acquired ichthyosiform skin condition, the pattern of hsp27 expression resembles healthy human skin. Hsp27 expression was reduced in bullous ichthyosiform erythroderma and annular epidermolytic ichthyosis, and absent in X-linked recessive ichthyosis (1/3 patients) and congenital hemidysplasia with ichthyosiform nevus and limb defects syndrome (1/1). In X-linked dominant chondrodysplasia, 3 small samples are completely negative and 2 larger samples show a pattern resembling random X inactivation. In the mouse models, tattered and bare patches, representing the murine analogues to X-linked dominant chondrodysplasia and congenital hemidysplasia with ichthyosiform nevus and limb defects syndrome, expression of hsp25 (the murine homologue of hsp27) also showed lyonization, demonstrating a clear-cut link between hsp27 expression and underlying molecular pathology. Our results show that loss of hsp27 is a rare event in human epidermis that is associated with specific genetic defects. Among the cases described here, these defects are either in suprabasal keratins or in enzymes involved in cholesterol biosynthesis. The expression and chaperone function of hsp27 might be modified by low/absent epidermal cholesterol and aberrant substrates (ie, keratins) resulting in protein misfolding, dyskeratosis, and thus contribute to the ichthyotic phenotype.

Molecular genetics of the ichthyoses

The ichthyoses are a large, clinically, genetically, and etiologically heterogeneous group of disorders of cornification due to abnormal differentiation and desquamation of the epidermis. Although they differ in clinical features, inheritance, and structural and biochemical abnormalities of the epidermis, they often pose a diagnostic challenge. For each of the 12 ichthyoses and related disorders described here, the major disease genes have been identified and genotype-phenotype correlation have begun to emerge. The molecular findings reveal the functional importance and interactions of many different epidermal proteins and metabolic pathways, including major structural proteins (keratins, loricrin), enzymes involved in lipid metabolism (transglutaminase 1, lipoxygenases, fatty aldehyde dehydrogenase, steroid sulfatase, glucocerebrosidase, Delta8-Delta7 sterol isomerase, 3beta-hydroxysteroid dehydrogenase), and protein catabolism (LEKTI), peroxisomal transport and processing (Peroxin 7 receptor, Phytanoyl-CoA hydroxylase) and DNA repair (proteins of the transcription repair complex). This review highlights the spectacular advances in the molecular genetics and biology of heritable ichthyoses over the past decade. It illustrates the power of molecular diagnostics for refining disease classification, providing prenatal diagnosis, improving genetic counseling, and clinical management.

Epidermal desquamation

Epidermal desquamation, a continuous but insensible bodily activity, is largely ignored unless the rate or amount of scale production becomes abnormal. It is the last topic to be considered in any serious discussion of epidermal growth and differentiation, but is becoming an increasingly fertile ground for investigation. This review summarizes: (a) methods for measuring desquamation; (b) variables that affect normal desquamation; (c) mechanisms of desquamation; (d) the role of desquamation in nutritional homeostasis; and (e) the role of desquamation as a first line of defense. Consideration is given to whether desquamation might be harnessed to eliminate or remediate toxins that have accumulated in the body.

Direct perturbation of lens membrane structure may contribute to cataracts caused by U18666A, an oxidosqualene cyclase inhibitor

Induction of cataracts in experimental animals is a common toxic feature of oxidosqualene cyclase (OSC) inhibitors. U18666A has been shown to produce irreversible lens damage within a few weeks of treatment. Drug actions, besides reducing the availability of cholesterol, could contribute to cataract formation. Cholesterol added to cultures of lens epithelial cells could only partially overcome the growth-inhibiting effects of U18666A. In view of this finding and the fact that U18666A and other OSC inhibitors are highly lipophilic cationic tertiary amines, we tested the hypothesis that the cataractogenic effect of U18666A is related to direct perturbation of lens membrane structure and function. Based on changes in the anisotropy of fluorescent probes, U18666A incorporated into bovine lens lipid model membranes increased membrane structural order and, using small-angle x-ray diffraction, U18666A was shown to intercalate into the lens lipid model membranes and produce a broad condensing effect on membrane structure. Also, exposure of cultured lens epithelial cells and intact rat lenses to U18666A induced apoptosis. Induction of apoptosis may begin by intercalation of U18666A into cell membranes. By increasing membrane structural order, U18666A may also increase light scatter, thus directly contributing to lens opacification.

Late gestational lung hypoplasia in a mouse model of the Smith-Lemli-Opitz syndrome

Background

Normal post-squalene cholesterol biosynthesis is important for mammalian embryonic development. Neonatal mice lacking functional dehydrocholesterol Δ7-reductase (Dhcr7), a model for the human disease of Smith-Lemli-Opitz syndrome, die within 24 hours of birth. Although they have a number of biochemical and structural abnormalities, one cause of death is from apparent respiratory failure due to developmental pulmonary abnormalities.

Results

In this study, we characterized further the role of cholesterol deficiency in lung development of these mice. Significant growth retardation, beginning at E14.5~E16.5, was observed in Dhcr7^-/- embryos. Normal lobation but smaller lungs with a significant decrease in lung-to-body weight ratio was noted in Dhcr7^-/- embryos, compared to controls. Lung branching morphogenesis was comparable between Dhcr7^-/- and controls at early stages, but delayed saccular development was visible in all Dhcr7^-/- embryos from E17.5 onwards. Impaired pre-alveolar development of varying severity, inhibited cell proliferation, delayed differentiation of type I alveolar epithelial cells (AECs) and delayed vascular development were all evident in knockout lungs. Differentiation of type II AECs was apparently normal as judged by surfactant protein (SP) mRNAs and SP-C immunostaining. A significant amount of cholesterol was detectable in knockout lungs, implicating some maternal transfer of cholesterol. No significant differences of the spatial-temporal localization of sonic hedgehog (Shh) or its downstream targets by immunohistochemistry were detected between knockout and wild-type lungs and Shh autoprocessing occurred normally in tissues from Dhcr7^-/- embryos.

Conclusion

Our data indicated that cholesterol deficiency caused by Dhcr7 null was associated with a distinct lung saccular hypoplasia, characterized by failure to terminally differentiate alveolar sacs, a delayed differentiation of type I AECs and an immature vascular network at late gestational stages. The molecular mechanism of impaired lung development associated with sterol deficiency by Dhcr7 loss is still unknown, but these results do not support the involvement of dysregulated Shh-Patched-Gli pathway in causing this defect.

Analysis of mesenchymal cells derived from an chondrodysplasia punctuate patient and donors

Conradi-Hunermann syndrome (CDPX2) is X-linked dominant disorder appeared with aberrant punctuate calcification. The skeletal cells derived from the marrow stroma are active in maintaining the skeletal formation. We obtained mesenchymal stem cells from a patient with CDPX2 and studied the formation of colony forming unit-fibroblast (CFU-F) in vitro in comparison cells obtained from normal donors. Cultured cells were studied morphologically and subjected to gene expression analysis. Marrow stromal cells (MSC)-chondrodysplasia punctuate (CDP) cells from CDPX2 were identified by their mosaic morphology formed three phenotypically distinct types of CFU-F colonies. One type consisted of normal fibroblasts with developed cell body and cellular processes; the second type contained pathological small cells without processes; and the third type comprised of mixed cells. We compared gene expression by the MSC-CDP to cells from normal donors. Transcription factors analyzed proliferation potential were similar in both normal and mixed colonies of MSC-CDP and similar to normal MSCs. The message expression for cytokines and extra cellular matrix (ECM) proteins revealed similar expression for biglycan, osteocalcin, and osteonectin, while IL-6, IL-11, and M-CSF mRNA levels were significantly higher in normal cells than in MSC-CDP. Mixed cells had elevated levels for IL-6 and M-CSF mRNA, but expressed IL-11 at the normal range. The studied genes were expressed at lower levels by the pathological (MSC-CDP) cells compared to normal ones. Hence, MSC-CDP was demonstrated to display abnormal morphology and transcription of several investigated genes. This study further illuminates the basis of the mosaic pattern of mesenchymal cells derived from a patient affected with CDPX2, and their gene expression involvement.

Human malformation syndromes due to inborn errors of cholesterol synthesis

PURPOSE OF REVIEW

This review covers a group of human malformation syndromes, which are caused by inborn errors of cholesterol synthesis. The Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive, multiple malformation, and mental retardation syndrome that is the prototypical example of this group of disorders. In the 10 years since the biochemical cause of SLOS was identified, other malformation syndromes have been shown to result from defects in this pathway. These include desmosterolosis, lathosterolosis, X-linked dominant chondrodysplasia punctata type 2 (CDPX2), congenital hemidysplasia with ichthyosiform erythroderma and limb defects (CHILD syndrome), hydrops-ectopic calcification-moth-eaten skeletal dysplasia (HEM dysplasia), and some cases of Antley-Bixler syndrome. These disorders represent the first true merging of dysmorphology with biochemical genetics.

RECENT FINDINGS

Recent studies report the identification of human lathosterolosis patients, indicate that SLOS is a relatively common genetic disorder that may be a major unrecognized cause of fetal loss, suggest that correction of the biochemical defect can improve central nervous system function, and show that perturbed sonic hedgehog signaling due to decreased sterol levels likely underlies some of the malformations in SLOS and lathosterolosis.

SUMMARY

Recognition of the biochemical defect in these syndromes has given insight into the role that cholesterol plays during normal development, into understanding the pathophysiological processes that underlie the clinical problems found in these disorders, and into developing therapeutic interventions.

Left-sided CHILD syndrome caused by a nonsense mutation in the NSDHL gene

Congenital hemidysplasia with ichthyosiform nevus and limb defects (CHILD) syndrome is a rare X-linked dominant malformation syndrome characterized by unilaterally distributed ichthyosiform nevi, often sharply delimited at the midline, and ipsilateral limb defects. At least two-thirds of cases demonstrate involvement of the right side. Mutations in an essential enzyme of cholesterol biosynthesis, NAD(P)H steroid dehydrogenase-like [NSDHL], have been reported in five unrelated patients with right-sided CHILD syndrome and in a sixth patient with bilaterally, symmetric nevi and mild skeletal anomalies, but not with CHILD syndrome as originally defined. Although all of the molecularly diagnosed cases with the CHILD phenotype to date have had right-sided disease, we report here a novel nonsense mutation (E151X) of NSDHL in an infant with left-sided CHILD syndrome. This result demonstrates that both right- and left-sided CHILD syndrome can be caused by mutations in the same gene.

Sterol regulatory element-binding protein-2 interacts with hepatocyte nuclear factor-4 to enhance sterol isomerase gene expression in hepatocytes

In the course of an effort to identify unknown targets genes for sterol regulatory element-binding proteins (SREBPs) by PCR, the gene for ATP citrate-lyase was determined to be one such gene. (Sato, R., Okamoto, A., Inoue, J., Miyamoto, W., Sakai, Y., Emoto, N., Shimano, H., and Maeda, M. (2000) J. Biol. Chem. 275, 12497-12502). We here report that gene expression of sterol Delta8-isomerase (SI), which catalyzes the conversion of the 8-ene isomer into the 7-ene isomer in the last steps of the cholesterol biosynthetic pathway, is regulated by SREBPs, mainly by SREBP-2. Luciferase assays using the promoter of the human SI gene revealed that a 200-base pair segment upstream region from the transcription start site contains functional elements required for the activity of the SREBPs, Sp1 and NF-Y. Interestingly, SI gene expression was well regulated by sterols in Caco-2 and HepG2 cells, in contrast with HEK293 and HeLa cells. Overexpression of hepatocyte nuclear factor (HNF)-4 in HEK293 cells augmented expression of SREBP-responsive genes including the SI gene, whereas inactivation of HNF-4 by small interfering RNAs in HepG2 cells reduced the SI gene promoter activity. The in vitro pull-down and in vivo co-immunoprecipitation experiments showed the direct interaction between SREBP-2 and HNF-4. These data provide a novel pathway by which HNF-4 potentiates the SREBP functions and stimulates expression of SREBP-responsive genes in enterohepatic cells.

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.

Identification of two novel mutations in the murine Nsdhl sterol dehydrogenase gene and development of a functional complementation assay in yeast

Nsdhl is a 3beta-hydroxysterol dehydrogenase that is involved in the removal of C-4 methyl groups in the cholesterol biosynthetic pathway. Mutations in this gene are associated with the X-linked male lethal mouse mutations bare patches (Bpa) and striated (Str) and human CHILD syndrome. We have now detected the missense mutations V53D and A94T in conserved amino acids in two additional Bpa alleles. The latter alters the same amino acid as a missense mutation found in two unrelated CHILD patients, strongly suggesting that differences in the phenotype between Bpa mice and females with CHILD syndrome are unlikely to be explained by different types or sites of mutations. We have also demonstrated that the mouse NSDHL protein can rescue the lethality of erg26 deficient cells of Saccharomyces cerevisiae that lack the yeast ortholog, substantiating the role of NSDHL as a C-3 sterol dehydrogenase. Using this in vivo assay, we have demonstrated that two Str alleles function as hypomorphs, while three Bpa and one Str allele provide no complementation or rescue.

Embryonic expression of cholesterogenic genes is restricted to distinct domains and colocalizes with apoptotic regions in mice

Cholesterol biosynthesis has been assumed to be an ubiquitous process in vertebrate organisms. Here we present data demonstrating that expression of key enzymes of cholesterol biosynthesis is restricted to specific tissues during embryonic development. Distinct expression starts in the dorsal neural tube at embryonic day 8 and is later detected in dorsal root and cephalic ganglia, in the pharyngeal pouches and limb buds. In the limb, expression becomes progressively restricted to interdigital regions during differentiation. Caspase3 whole mount immunostaining revealed that cholesterol biosynthesis colocalizes with apoptotic regions that are targets of the morphogenic signal Sonic hedgehog. This expression pattern correlates closely with the shared phenotypic features of cholesterol biosynthesis and hedgehog mutants.

Fetus with an unusual form of nonrhizomelic chondrodysplasia punctata: case report and review

Chondrodysplasia punctata (CDP) is a heterogeneous condition mainly characterized by premature and ectopic calcification of cartilage. Many genetic and nongenetic causes have been described leading to a preliminar etiological classification into defects of peroxisomal metabolism, defects in cholesterol metabolism, and vitamin K (vit K) metabolism. However, numerous cases of CDP still remain unclassified. The difficulties in reaching a causal diagnosis are illustrated here by a 23-week-old fetus with nonrhizomelic CDP characterized by extensive cartilage stippling, brachyphalangy, and nasal hypoplasia.

Biochemical abnormality associated with Smith-Lemli-Opitz syndrome in an infant with features of Rutledge multiple congenital anomaly syndrome confirms that the latter is a variant of the former

We describe a female infant with morphologic features of Rutledge multiple-congenital-anomaly syndrome (RMCAS) and biochemical features of Smith-Lemli-Opitz syndrome (SLOS). She had microcephaly with hypoplastic cerebral frontal lobes and cerebellum, agenesis of the splenium of corpus callosum, abnormal facies including hypertelorism with bilateral inner epicanthal folds, a broad nasal bridge with slightly anteverted nares and patent choanae, low set ears and complex conchal formation, high-arched palate and thick maxillary alveolar ridges, and micrognathia. Her chest was broad, genitalia were ambiguous, and uterus was bicornuate. Skeletal abnormalities included a hypoplastic appendicular skeleton, post-axial hexadactyly of the right hand and the left foot, syndactyly of bilateral 2nd-3rd toes and left 5th-6th toes, right talipes varus and left talipes valgus, and fused L5-S1 vertebrae. Congenital heart disease consisted of hypoplastic left heart, coronary sinus agenesis, ostium secundum and ostium primum defects, and a thickened septum primum. The lungs were hypolobated and the kidneys manifested oligopapillary hypoplasia. Total colonic Hirschsprung disease was noted microscopically. Analysis of liver tissue taken at postmortem examination revealed the ratio of 7-dehydrocholesterol and cholesterol to be 143 (expected, 0.28 +/- 0.28). Although initially described as a distinct syndrome, RMCAS was merged with the severe form of SLOS, because of significantly overlapping features [Online Mendelian Inheritance in Man (OMIM) #268670]. The biochemical data showing an excess of 7-dehydrocholesterol and low cholesterol in the liver tissue of our case supports this viewpoint.

Autosomal recessive HEM/Greenberg skeletal dysplasia is caused by 3 beta-hydroxysterol delta 14-reductase deficiency due to mutations in the lamin B receptor gene

Hydrops-ectopic calcification-"moth-eaten" (HEM) or Greenberg skeletal dysplasia is an autosomal recessive chondrodystrophy with a lethal course, characterized by fetal hydrops, short limbs, and abnormal chondro-osseous calcification. We found elevated levels of cholesta-8,14-dien-3beta-ol in cultured skin fibroblasts of an 18-wk-old fetus with HEM, compatible with a deficiency of the cholesterol biosynthetic enzyme 3beta-hydroxysterol delta(14)-reductase. Sequence analysis of two candidate genes encoding putative human sterol delta(14)-reductases (TM7SF2 and LBR) identified a homozygous 1599-1605TCTTCTA-->CTAGAAG substitution in exon 13 of the LBR gene encoding the lamin B receptor, which results in a truncated protein. Functional complementation of the HEM cells by transfection with control LBR cDNA confirmed that LBR encoded the defective sterol delta(14)-reductase. Mutations in LBR recently have been reported also to cause Pelger-Huët anomaly, an autosomal dominant trait characterized by hypolobulated nuclei and abnormal chromatin structure in granulocytes. The fact that the healthy mother of the fetus showed hypolobulated nuclei in 60% of her granulocytes confirms that classic Pelger-Huët anomaly represents the heterozygous state of 3beta-hydroxysterol delta(14)-reductase deficiency.

X-linked recessive chondrodysplasia punctata: spectrum of arylsulfatase E gene mutations and expanded clinical variability

X-linked chondrodysplasia punctata (CDPX1), due to mutations of the arylsulfatase E (ARSE) gene, is a congenital disorder characterized by abnormalities in cartilage and bone development. We performed mutational analysis of the ARSE gene in a series of 16 male patients, and we found mutations in 12 subjects. Clinical variability was observed among the patients, including severe presentations with early lethality in one of them, and symptoms such as cataract and respiratory distress. This indicates that the clinical spectrum of CDPX1, commonly considered a relatively mild form of chondrodysplasia punctata, is wider than previously reported. Different types of mutations were found among the patients examined. Three missense mutations (I80N, T481M, P578S) were expressed in Cos7 cells to study the effects on arylsulfatase E catalytic activity. These mutations caused impaired enzymatic activity suggesting that they are responsible for the disease. Two nonsense mutations, W581X in four patients and R540X in one, were found. One patient showed an insertion (T616ins). In three patients we found deletions of the ARSE gene: in one the deletion involved only the 3' end of the gene, while in two the ARSE gene was completely deleted.

Molecular, biochemical, and phenotypic analysis of a hemizygous male with a severe atypical phenotype for X-linked dominant Conradi-Hunermann-Happle syndrome and a mutation in EBP

X-linked dominant Conradi-Hunermann-Happle syndrome (CDPX2; MIM 302960) is a rare chondrodysplasia punctata primarily affecting females. CDPX2 is presumed lethal in males, although a few affected males have been reported. CDPX2 is a cholesterol biosynthetic disorder due to 3-beta-hydroxysteroid-delta8,delta7-isomerase deficiency caused by mutations in the emopamil binding protein (EBP) gene. A 2.5-year-old Caucasian male was followed from the age of 6 weeks and noted to have significant developmental delay, hypotonia, seizures, and patchy hypopigmentation. Multiple congenital anomalies included a unilateral cataract, esotropia, crossed renal ectopia, stenotic ear canals, and failure to thrive, requiring G-tube placement. Multiple minor anomalies and ptosis were noted. No skeletal asymmetry or chondrodysplasia punctata were noted on skeletal survey at 6 weeks and 13 months. An extensive genetic work-up including cholesterol (126-176 mg/dl) and 7-dehydrocholesterol was unrevealing. However, the levels of 8(9)-cholestenol and 8-dehydrocholesterol were mildly increased in plasma, which was confirmed in cultured fibroblasts. This prompted molecular analysis of the EBP gene, which revealed a novel hemizygous (nonmosaic) mutation in exon 2 (L18P). Two restriction digests were developed that confirmed this mutation in skin fibroblasts, blood, and buccal cells (all nonmosaic). We determined that the patient's mother (adopted) also has the L18P mutation enabling prenatal diagnosis of a normal male fetus. She has normal stature, no asymmetry, no cataracts at this time, and has a patch of hyperpigmentation on her chest best visualized on Woods lamp examination, characteristic of CDPX2. The mild maternal phenotype has been described previously. However, this nonmosaic missense mutation has resulted in a severe phenotype in her surviving son.

X-linked dominant chondrodysplasia punctata (CDPX2) caused by single gene mosaicism in a male

X-linked dominant chondrodysplasia punctata (CDPX2; Happle syndrome) is recognized almost exclusively in females, who display mosaic and asymmetric features, presumed to arise secondary to random X-inactivation. CDPX2 results from mutation of an X-linked gene coding for sterol-delta(8)-delta(7) isomerase (emopamil binding protein). We describe a boy with clinical features of CDPX2 (including those presumed to arise usually secondary to functional mosaicism in females). Biochemical and molecular studies demonstrate that he is mosaic for a sterol-delta(8)-delta(7) isomerase gene mutation. He is the first reported example of single gene mosaicism giving rise to CDPX2 in a male.