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

Repurposing Clemastine to Target Glioblastoma Cell Stemness

Brain tumor-initiating cells (BTICs) and tumor cell plasticity promote glioblastoma (GBM) progression. Here, we demonstrate that clemastine, an over-the-counter drug for treating hay fever and allergy symptoms, effectively attenuated the stemness and suppressed the propagation of primary BTIC cultures bearing PDGFRA amplification. These effects on BTICs were accompanied by altered gene expression profiling indicative of their more differentiated states, resonating with the activity of clemastine in promoting the differentiation of normal oligodendrocyte progenitor cells (OPCs) into mature oligodendrocytes. Functional assays for pharmacological targets of clemastine revealed that the Emopamil Binding Protein (EBP), an enzyme in the cholesterol biosynthesis pathway, is essential for BTIC propagation and a target that mediates the suppressive effects of clemastine. Finally, we showed that a neural stem cell-derived mouse glioma model displaying predominantly proneural features was similarly susceptible to clemastine treatment. Collectively, these results identify pathways essential for maintaining the stemness and progenitor features of GBMs, uncover BTIC dependency on EBP, and suggest that non-oncology, low-toxicity drugs with OPC differentiation-promoting activity can be repurposed to target GBM stemness and aid in their treatment.

Commercial Gene Panels for Congenital Anterior Segment Anomalies: Are They All the Same?

PURPOSE

We compared next generation sequencing multigene panels (NGS-MGP) from 5 commercial laboratories to inform ophthalmologists' decision making in diagnostic genetic testing for congenital anterior segment anomalies (CASAs).

DESIGN

Comparison of commercial genetic testing panels.

METHODS

This observational study gathered publicly available information on NGS-MGP from 5 commercial laboratories for the following: cataracts, glaucoma, anterior segment dysgenesis (ASD), microphthalmia-anophthalmia-coloboma (MAC), corneal dystrophies, and Axenfeld-Rieger syndrome (ARS). We compared gene panel composition, consensus rate (genes covered by all the panels per condition, "concurrent"), dissensus rate (genes covered by only 1 panel per condition, "standalone"), and intronic variant coverage. For individual genes, we compared publication history and association with systemic conditions.

RESULTS

Altogether, cataract, glaucoma, corneal dystrophies, MAC, ASD, and ARS panels tested 239, 60, 36, 292, and 10 discrete genes, respectively. The consensus rate varied between 16% and 50%, and the dissensus rate varied between 14% and 74%. After pooling concurrent genes from all conditions, 20% of these genes were concurrent in 2 or more conditions. For both cataract and glaucoma, concurrent genes had significantly stronger correlation with the condition than standalone genes.

CONCLUSIONS

The genetic testing of CASAs using NGS-MGPs is complicated, owing to their number, variety, and phenotypic and genetic overlap. Although the inclusion of additional genes, such as the standalone ones, might increase diagnostic yield, these genes are also less well studied, indicating uncertainty over their role in CASA pathogenesis. Rigorous prospective diagnostic yield studies of NGS-MGPs will aid in making decisions of panel selection for the diagnosis of CASAs.

Syndromic ichthyoses

Inherited ichthyoses are classified as Mendelian disorders of cornification (MEDOC), which are further defined on the basis of clinical and genetic features and can be divided into non-syndromic and syndromic forms. To date, mutations in more than 30 genes are known to result in various types of syndromic ichthyoses, which, in addition to mostly generalised scaling and hyperkeratosis of the skin, also show additional organ involvement. The syndromic ichthyoses are generally very rare and are classified based on the mode of inheritance, and can be further subdivided according to the predominant symptoms. In our review we provide a concise overview of the most prevalent syndromic forms of ichthyosis within each subgroup. We emphasize the importance of the clinical assessment of complex syndromes even in the era of genetic testing as a first-tier diagnostic and specifically the need to actively assess potential organ involvement in patients with ichthyosis, thereby enabling efficient diagnostic and therapeutic approaches and timely access to specialized centers for rare disorders of cornifications. As part of the Freiburg Center for Rare Diseases a Center for Cornification Disorders was recently established with collaboration of the Institute of Human Genetics and the Department of Dermatology. An early diagnosis of syndromes will be of direct benefit to the patient regarding interventional and therapeutic measures e. g. in syndromes with cardiac or metabolic involvement and allows informed reproductive options and access to prenatal and preimplantation genetic diagnosis in the family.

Conradi-Hünermann-Happle syndrome: Clinical and trichoscopic findings

Conradi-Hünermann-Happle syndrome (CHHS) is a rare genodermatosis resulting from mutations in the EBP (emopamil binding protein) gene. Dermatologic manifestations may include cicatricial alopecia, ichthyosis, follicular atrophoderma, pigmentary abnormalities, and nail dystrophy. In addition to genetic testing and clinical findings, trichoscopic findings may aid in the diagnosis. In this case report, we discuss the trichoscopic findings in a 3-year-old girl with CHHS and how these findings help us understand the pathophysiology of this disease.

Thundering hoofbeats and dazzling zebras: A model integrating current rare disease perspectives in paleopathology

OBJECTIVE

The article reviews the study of rare diseases and their nomenclature, emerging government policies and initiatives, and the concerns voiced by the modern rare disease communities. An interpretive model is then presented for the bioarchaeological interpretations of individuals with paleopathological evidence of rare diseases.

MATERIALS

In demonstration of the application of the proposed framework, we evaluate the skeletal remains of an adult female (EZ 3-7-1) excavated in the 1980s from the Middle Woodland (50BCE-CE400) context of the Elizabeth site (11PK512) in the lower Illinois Valley, USA.

METHODS

We use macroscopic examination methods, as well as cementochronology, to put forth the osteobiographical profile.

RESULTS

The skeletal manifestations observed suggests limitations of major life activities, which would have increased in severity throughout the life course of EZ 3-7-1.

CONCLUSIONS

The study of EZ 3-7-1 demonstrates how an osteobiography, centering on the lived experiences and limitations throughout a life course, can allow for a deeper appreciation for life in the past.

SIGNIFICANCE

By considering the perspectives of the modern rare disease community in the bioarchaeological methodology, research can include the nuanced impacts of the disease on life experiences and varying societal perceptions and attitudes, as well as raising awareness and advancing contemporary perspectives on impairment and disability.

LIMITATIONS

Without ample contextual evidence, there are limitations in making conclusions regarding social identity and disability.

SUGGESTIONS FOR FURTHER RESEARCH

This framework should be applied to other rare diseases in a variety of contexts to further test its functionality.

Sterol Biosynthesis Inhibition in Pregnant Women Taking Prescription Medications

Sterol biosynthesis is a critical homeostatic mechanism of the body. Sterol biosynthesis begins during early embryonic life and continues throughout life. Many commonly used medications, prescribed >200 million times in the United States annually, have a sterol biosynthesis inhibition side effect. Using our high-throughput LC-MS/MS method, we assessed the levels of post-lanosterol sterol intermediates (lanosterol, desmosterol, and 7-dehydrocholesterol (7-DHC)) and cholesterol in 1312 deidentified serum samples from pregnant women. 302 samples showing elevated 7-DHC were analyzed for the presence of 14 medications known to inhibit the 7-dehydrocholesterol reductase enzyme (DHCR7) and increase 7-DHC. Of the 302 samples showing 7-DHC elevation, 43 had detectable levels of prescription medications with a DHCR7-inhibiting side effect. Taking more than one 7-DHC-elevating medication in specific combinations (polypharmacy) might exacerbate the effect on 7-DHC levels in pregnant women, suggesting a potentially additive or synergistic effect. As 7-DHC and 7-DHC-derived oxysterols are toxic, and as DHCR7-inhibiting medications are considered teratogens, our findings raise potential concerns regarding the use of prescription medication with a DHCR7-inhibiting side effect during pregnancy. The use of prescription medications during pregnancy is sometimes unavoidable, but choosing a medication without a DHCR7-inhibiting side effect might lead to a heathier pregnancy and prevent putatively adverse outcomes for the developing offspring.

Thermostabilization of Membrane Proteins by Consensus Mutation: A Case Study for a Fungal Δ8-7 Sterol Isomerase

Membrane proteins are generally challenging to work with because of their notorious instability. Protein engineering has been used increasingly to thermostabilize labile membrane proteins such as G-protein-coupled receptors for structural and functional studies in recent years. Two major strategies exist. Scanning mutagenesis systematically eliminates destabilizing residues, whereas the consensus approach assembles mutants with the most frequent residues among selected homologs, bridging sequence conservation with stability. Here, we applied the consensus concept to stabilize a fungal homolog of the human sterol Δ8-7 isomerase, a 26.4 kDa protein with five transmembrane helices. The isomerase is also called emopamil-binding protein (EBP), as it binds this anti-ischemic drug with high affinity. The wild-type had an apparent melting temperature (T_m) of 35.9 °C as measured by the fluorescence-detection size-exclusion chromatography-based thermostability assay. A total of 87 consensus mutations sourced from 22 homologs gained expression level and thermostability, increasing the apparent T_m to 69.9 °C at the cost of partial function loss. Assessing the stability and activity of several systematic chimeric constructs identified a construct with an apparent T_m of 79.8 °C and two regions for function rescue. Further back-mutations of the chimeric construct in the two target regions yielded the final construct with similar apparent activity to the wild-type and an elevated T_m of 88.8 °C, totaling an increase of 52.9 °C. The consensus approach is effective and efficient because it involves fewer constructs compared with scanning mutagenesis. Our results should encourage more use of the consensus strategy for membrane protein thermostabilization.

Prenatal diagnosis of fetal skeletal dysplasia using targeted next-generation sequencing: an analysis of 30 cases

Background

This study aims to provide genetic diagnoses for 30 cases of fetal skeletal dysplasia, and a molecular basis for the future prenatal diagnosis of fetal skeletal dysplasia.

Methods

A total of 30 cases of fetal skeletal dysplasia detected with ultrasound between January 2014 and June 2017 were analyzed. Among these fetuses, 15 fetuses had local skeletal malformations, while 15 fetuses had short limb malformations. Samples of fetal umbilical cord blood, amniotic fluid, and/or aborted tissue were collected from all cases. Karyotyping, whole genome sequencing, and targeted next-generation sequencing of skeletal disease-related pathogenic genes were performed, as needed. Blood samples were taken from the parents for verification using Sanger sequencing.

Results

Among the 30 cases of fetal skeletal dysplasia, two cases were diagnosed with trisomy 18. However, none of these cases were identified with any microdeletions or microreplications associated with skeletal dysplasia. Among the 28 chromosomally normal cases with fetal skeletal dysplasia, 21 cases were detected with mutations in genes related to skeletal diseases. Furthermore, collagen gene mutations were detected in six fetuses with short limb malformations, while heterozygous disease-causing mutations in the fibroblast growth factor receptor 3 (FGFR3) gene were detected in seven fetuses. The remaining fetuses carried mutations in other various genes, including tumor protein p63 (TP63), cholestenol delta-isomerase (EBP), cholinergic receptor nicotinic gamma subunit (CHRNG), filamin B (FLNB), and SRY-box 9 (SOX9). Three compound heterozygous mutations in CHRNG, COL11A2 and SOX9 were carried by phenotypically healthy parents.

Conclusion

Targeted next-generation sequencing can significantly improve the prenatal diagnoses of fetal skeletal dysplasia, providing parents with more precision medicine, and improved genetic counseling.

X-linked dominant chondrodysplasia punctata with severe phenotype in a female fetus: A case report

RATIONALE

X-linked dominant chondrodysplasia punctata type 2 (CDPX2) is a condition involving facial, skin, and skeletal dysplasia as a result of a mutation in emopamil binding protein (EBP). It usually presents with mild symptoms in female patients but is fatal in male patients.

PATIENT CONCERNS

A fetus was diagnosed with asymmetrical short limbs and a narrow and small thorax by prenatal ultrasound examination at 24+5 weeks gestation. The pregnancy was terminated at 27 weeks of gestation; gross examination, postnatal X-ray and, whole exome analysis were performed to clarify the diagnosis.

DIAGNOSIS

A provisional diagnosis of fatal skeletal dysplasia was given and the definite diagnosis of CDPX2 was based on postnatal X-ray and genetic testing of the aborted fetus.

INTERVENTION

The pregnancy was terminated at 27 weeks' gestation after a fetal ultrasound indicated a severe abnormal phenotype.

OUTCOMES

Whole exome analysis of aborted tissue confirmed EBP mutation in this case. Unlike most case reports, this female patient presented a severe phenotype that was considered to be related to X-chromosome inactivation.

LESSONS

Chondrodysplasia punctata (CDP) should be considered if prenatal ultrasound shows high punctuate echoes at the metaphysis of long bones and asymmetrical short lower limbs. Postnatal X-ray and measurement of sterol levels in the amniotic fluid may aid in the diagnosis of CDP, but the condition can be confirmed with genetic testing of a blood sample or aborted tissue after delivery.

New splicing pathogenic variant in EBP causing extreme familial variability of Conradi-Hünermann-Happle Syndrome

X-linked dominant chondrodysplasia punctata (CDPX2 or Conradi-Hünermann-Happle syndrome, MIM #302960) is caused by mutations in the EBP gene. Affected female patients present with Blaschkolinear ichthyosis, coarse hair or alopecia, short stature, and normal psychomotor development. The disease is usually lethal in boys. Nevertheless, few male patients have been reported; they carry a somatic mosaicism in EBP or present with Klinefelter syndrome. Here, we report CDPX2 patients belonging to a three-generation family, carrying the splice variant c.301 + 5 G > C in intron 2 of EBP. The grandfather carries the variant as mosaic state and presents with short stature and mild ichthyosis. The mother also presents with short stature and mild ichthyosis and the female fetus with severe limb and vertebrae abnormalities and no skin lesions, with random X inactivation in both. This further characterizes the phenotypical spectrum of CDPX2, as well as intrafamilial variability, and raises the question of differential EBP mRNA splicing between the different target tissues.

Concurrent Chondrodysplasia Punctata Type 2 (Conradi-Hunermann-Happle Syndrome) and Ichthyosis Vulgaris in Teenaged Twin Girls

We present concurrent X-linked chondrodysplasia punctata and ichthyosis vulgaris in adolescent fraternal twin girls, notable for initial presentation with dry skin in adolescence, characterized by dark-brown scale typical of ichthyosis vulgaris and blaschkolinear, atrophic, scaly plaques. This constellation of findings prompted further genetic investigation. Using a multigene approach to examine 39 genes associated with congenital ichthyosis, next-generation sequencing revealed a novel heterozygous missense mutation at a mutational hotspot in the EBP gene c.439C>T (p.R147C) in conjunction with a single nonsense mutation in the FLG gene (p.R501X) in both sisters. These individuals highlight the clinical variability of Conradi-Hunermann-Happle syndrome, illustrate the possibility of co-occurrence of rare and common forms of ichthyosis, and demonstrate the utility of multigene analysis.

Radiographic features of the skeleton in disorders of post-squalene cholesterol biosynthesis

Disorders of post-squalene cholesterol biosynthesis are inborn errors of metabolism characterised by multiple congenital abnormalities, including significant skeletal involvement. The most frequent and best-characterised example is the Smith-Lemli-Opitz syndrome. Nine other disorders are known, namely autosomal-recessive Antley-Bixler syndrome, Greenberg dysplasia, X-linked dominant chondrodysplasia punctata, X-linked recessive male emopamil-binding protein deficiency, CHILD syndrome, CK syndrome, sterol C4 methyloxidase-like deficiency, desmosterolosis and lathosterolosis. This study provides an overview of the radiologic features observed in these diseases. A common pattern of limb abnormalities is recognisable, including polydactyly, which is typically post-axial and rarely interdigital and can involve all four limbs, and syndactyly of the toes. Chondrodysplasia punctata is specifically associated with a subgroup of disorders of cholesterol biosynthesis (Greenberg dysplasia, CHILD syndrome, X-linked dominant chondrodysplasia punctata, male emopamil-binding protein deficiency). The possible occurrence of epiphyseal stippling in the Smith-Lemli-Opitz syndrome, initially reported, does not appear to be confirmed. Stippling is also associated with other congenital disorders such as chromosomal abnormalities, brachytelephalangic chondrodysplasia punctata (X-linked recessive chondrodysplasia punctata, disruptions of vitamin K metabolism, maternal autoimmune diseases), rhizomelic chondrodysplasia punctata (peroxisomal disorders) and lysosomal storage disorders. In the differential diagnosis of epiphyseal stippling, a moth-eaten appearance of bones, asymmetry, or presence of a common pattern of limb abnormalities indicate inborn errors of cholesterol biosynthesis. We highlight the specific differentiating radiologic features of disorders of post-squalene cholesterol biosynthesis.

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.

Severe X-linked chondrodysplasia punctata in nine new female fetuses

OBJECTIVES

Conradi-Hünermann-Happle [X-linked dominant chondrodysplasia punctata 2 (CDPX2)] syndrome is a rare X-linked dominant skeletal dysplasia usually lethal in men while affected women show wide clinical heterogeneity. Different EBP mutations have been reported. Severe female cases have rarely been reported, with only six antenatal presentations.

METHODS

To better characterize the phenotype in female fetuses, we included nine antenatally diagnosed cases of women with EBP mutations. All cases were de novo except for two fetuses with an affected mother and one case of germinal mosaicism.

RESULTS

The mean age at diagnosis was 22 weeks of gestation. The ultrasound features mainly included bone abnormalities: shortening (8/9 cases) and bowing of the long bones (5/9), punctuate epiphysis (7/9) and an irregular aspect of the spine (5/9). Postnatal X-rays and examination showed ichthyosis (8/9) and epiphyseal stippling (9/9), with frequent asymmetric short and bowed long bones. The X-inactivation pattern of the familial case revealed skewed X-inactivation in the mildly symptomatic mother and random X-inactivation in the severe fetal case. Differently affected skin samples of the same fetus revealed different patterns of X-inactivation.

CONCLUSION

Prenatal detection of asymmetric shortening and bowing of the long bones and cartilage stippling should raise the possibility of CPDX2 in female fetuses, especially because the majority of such cases involve de novo mutations.

TM6SF2 and MAC30, new enzyme homologs in sterol metabolism and common metabolic disease

Carriers of the Glu167Lys coding variant in the TM6SF2 gene have recently been identified as being more susceptible to non-alcoholic fatty liver disease (NAFLD), yet exhibit lower levels of circulating lipids and hence are protected against cardiovascular disease. Despite the physiological importance of these observations, the molecular function of TM6SF2 remains unknown, and no sequence similarity with functionally characterized proteins has been identified. In order to trace its evolutionary history and to identify functional domains, we embarked on a computational protein sequence analysis of TM6SF2. We identified a new domain, the EXPERA domain, which is conserved among TM6SF, MAC30/TMEM97 and EBP (D8, D7 sterol isomerase) protein families. EBP mutations are the cause of chondrodysplasia punctata 2 X-linked dominant (CDPX2), also known as Conradi-Hünermann-Happle syndrome, a defective cholesterol biosynthesis disorder. Our analysis of evolutionary conservation among EXPERA domain-containing families and the previously suggested catalytic mechanism for the EBP enzyme, indicate that TM6SF and MAC30/TMEM97 families are both highly likely to possess, as for the EBP family, catalytic activity as sterol isomerases. This unexpected prediction of enzymatic functions for TM6SF and MAC30/TMEM97 is important because it now permits detailed experiments to investigate the function of these key proteins in various human pathologies, from cardiovascular disease to cancer.

A novel EBP c.224T>A mutation supports the existence of a male-specific disorder independent of CDPX2

Mutations in the Emopamil-binding protein (EBP) gene cause X-linked dominant chondrodysplasia punctata 2 (CDPX2), a disorder in which at least 95% of liveborn individuals are female and male intrauterine lethality is assumed. Several affected males with mutations in EBP have been reported. These males exhibit a phenotype similar to CDPX2 due to either somatic mosaicism or a 47, XXY karyotype in association with a null EBP allele. Alternatively, affected males may exhibit a distinct phenotype if they are hemizygous for a hypomorphic allele of EBP. Recently, we described a novel X-linked phenotype associated with digital abnormalities, intellectual disability and short stature, and mapped it to Xp11.4-p11.21. X-exome sequencing was performed to identify the mutated gene responsible for this phenotype. A novel missense variant, c.224T>A (p.I75N), was identified in EBP. SIFT and PolyPhen-2 predicted this change to be deleterious. The pathogenicity of this variant was subsequently supported by increased plasma levels of 8(9)-cholestenol in the proband and his mother. The molecular and biochemical evidence convincingly supports the pathogenicity and association of the p.I75N mutation with this newly described phenotype. This study expands the current phenotypic spectrum of males with hypomorphic EBP mutations and supports to the hypothesis that there exists an X-linked recessive entity independent of CDPX2.

Molecular pathways: sterols and receptor signaling in cancer

Accelerated cholesterol and lipid metabolism are the hallmarks of cancer and contribute to malignant transformation due to the obligatory requirement for cholesterol for the function of eukaryotic membranes. To build new membranes and maintain active signaling, cancer cells depend on high intensity of endogenous cholesterol biosynthesis and uptake of lipid particles. This metabolic dependency of cancer cells on cholesterol and other lipids is tightly regulated by the cholesterol homeostasis network, including (i) sterol response element-binding proteins (SREBP), master transcriptional regulators of cholesterol and fatty acid pathway genes; (ii) nuclear sterol receptors (liver X receptors, LXR), which coordinate growth with the availability of cholesterol; and (iii) lipid particle receptors, such as low-density lipid particle (LDL) receptor, providing exogenous sterol and lipids to cancer cells. In addition, activity of oncogenic receptors, such as MUC1 or EGFR, accelerates sterol uptake and biosynthesis. Therefore, a general strategy of reducing the cholesterol pool in cancer cells is challenged by the highly efficient feedback loops compensating for a blockade at a single point in the cholesterol homeostatic network. Besides the well-established structural role of cholesterol in membranes, recent studies have uncovered potent biologic activities of certain cholesterol metabolic precursors and its oxidized derivatives, oxysterols. The former, meiosis-activating sterols, exert effects on trafficking and signaling of oncogenic EGF receptor (EGFR). Cholesterol epoxides, the highly active products of cholesterol oxidation, are being neutralized by the distal sterol pathway enzymes, emopamyl-binding protein (EBP) and dehydrocholesterol-7 reductase (DHCR7). These recently discovered "moonlighting" activities of the cholesterol pathway genes and metabolites expand our understanding of the uniquely conserved roles these sterol molecules play in the regulation of cellular proliferation and in cancer.

The role of the abnormalities in the distal pathway of cholesterol biosynthesis in the Conradi-Hünermann-Happle syndrome

Conradi-Hünermann-Happle syndrome (CDPX2, OMIM 302960) is an inherited X-linked dominant variant of chondrodysplasia punctata (CP) caused by mutations in one gene of the distal pathway of cholesterol biosynthesis. It exhibits intense phenotypic variation and primarily affects the skin, bones and eyes. The ichthyosis following Blaschko's lines, chondrodysplasia punctata and cataracts are the typical clinical findings. The cardinal biochemical features are an increase in 8(9)-cholestenol and 8-dehydrocholesterol (8DHC), which suggest a deficiency in 3β-hydroxysteroid-Δ8,Δ7-isomerase, also called emopamil binding protein (EBP). The EBP gene is located on the short arm of the X chromosome (Xp11.22-p11.23) and encodes a 230 amino acid protein with dual function. Explaining the clinical phenotype in CDPX2 implies an understanding of both the genetics and biochemical features of this disease. CDPX2 displays an X-linked dominant pattern of inheritance, which is responsible for the distribution of lesions in some tissues. The clinical phenotype in CDPX2 results directly from impairment in cholesterol biosynthesis, and indirectly from abnormalities in the hedgehog signaling protein pathways. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Cholesterol metabolism deficiency

Genetic defects in enzymes responsible for cholesterol biosynthesis have emerged as important causes of congenital dysmorphology and retardation syndromes. Cholesterol is an important constituent of the cell membrane of most eukaryotic cells, in myelin formation in the brain, spinal cord, and peripheral nervous system, and acts as the precursor for steroid hormones and bile acids. Finally, cholesterol has important interactions with proteins, which control embryonic development. To date, eight distinct inherited disorders have been linked to different defects in cholesterol biosynthesis. Two result from an enzyme defect in the pre-squalene segment of the pathway: the classical form of mevalonic aciduria and the hyperimmunoglobulinemia D syndrome, also known as Dutch-type periodic fever. Six defects in the post-squalene segment of the pathway include: Smith-Lemli-Opitz syndrome, two X-linked dominant inherited and male-lethal disorders, Conradi-Hünermann-Happle syndrome and congenital hemidysplasia with ichthyosiform erythroderma and limb defects (CHILD), and at least three extremely rare autosomal recessive disorders, Greenberg skeletal dysplasia, lathosterolosis, and desmosterolosis. All these inborn errors known to date have been linked to deficiency of specific enzymes on the basis of elevated levels of specific sterol intermediates in tissues of affected patients followed by demonstrating disease-causing mutations in the encoding genes. These cholesterol deficiency multiple malformation-retardation syndromes have clinical overlap. Besides psychomotor retardation, developmental delay, structural brain malformations, multiple congenital anomalies, microcephaly, and cataract, impaired cholesterol biosynthesis is associated with autism and other behavioral disorders.

Disorders of sterol synthesis: beyond Smith-Lemli-Opitz syndrome

Since the discovery in 1993 that Smith-Lemli-Opitz syndrome (SLOS) is a disorder of cholesterol biosynthesis, human disorders associated with additional enzymes involved in the conversion of lanosterol to cholesterol have been identified. This review will focus primarily on the clinical aspects of these disorders, highlighting newly described syndromes, such as SC4MOL deficiency and CK syndrome. We will also provide clinical descriptions of additional cases for extremely rare disorders, such as desmosterolosis. We will compare and contrast the findings with those found in SLOS and briefly discuss possible mechanisms of disease pathogenesis.

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.

Clinical, molecular and biochemical characterization of nine Spanish families with Conradi-Hünermann-Happle syndrome: new insights into X-linked dominant chondrodysplasia punctata with a comprehensive review of the literature

BACKGROUND

Conradi-Hünermann-Happle syndrome (CDPX2, OMIM 302960) is an inherited X-linked dominant variant of chondrodysplasia punctata which primarily affects the skin, bones and eyes. CDPX2 results from mutations in EBP (emopamil binding protein), and presents with increased levels of sterol precursors 8(9)-cholesterol and 8-dehydrocholesterol.

OBJECTIVES

To expand the understanding of CDPX2, clinically, biochemically and genetically.

METHODS

We present one of the largest series reported to date, including 13 female patients belonging to nine Spanish families. Patients were studied biochemically using gas chromatography-mass spectrometry, genetically using polymerase chain reaction and in their methylation status using the HUMARA assay.

RESULTS

In our cases, there was a clear relationship between abnormal sterol profile and the EBP gene mutation. We describe three novel mutations in the EBP gene. EBP mutations were inherited in three out of nine families and were sporadic in the remaining cases.

CONCLUSIONS

No clear genotype-phenotype correlation was found. Patients' biochemical profiles did not reveal a relationship between sterol profiles and severity of disease. A skewed X-chromosome inactivation may explain the clinical phenotype in CDPX2 in some familial cases.

Cholesterol metabolism is required for intracellular hedgehog signal transduction in vivo

We describe the rudolph mouse, a mutant with striking defects in both central nervous system and skeletal development. Rudolph is an allele of the cholesterol biosynthetic enzyme, hydroxysteroid (17-beta) dehydrogenase 7, which is an intriguing finding given the recent implication of oxysterols in mediating intracellular Hedgehog (Hh) signaling. We see an abnormal sterol profile and decreased Hh target gene induction in the rudolph mutant, both in vivo and in vitro. Reduced Hh signaling has been proposed to contribute to the phenotypes of congenital diseases of cholesterol metabolism. Recent in vitro and pharmacological data also indicate a requirement for intracellular cholesterol synthesis for proper regulation of Hh activity via Smoothened. The data presented here are the first in vivo genetic evidence supporting both of these hypotheses, revealing a role for embryonic cholesterol metabolism in both CNS development and normal Hh signaling.

The molecules and signaling pathways that regulate growth and patterning of the developing embryo are still being elucidated, and one valuable experimental approach is the use of animal models, such as the mouse. We have identified a recessive mutation in the mouse, rudolph, that causes abnormal forebrain development and have determined that the mutated gene encodes hydroxysteroid (17-beta) dehydrogenase 7 gene, an enzyme necessary for cholesterol biosynthesis. Cholesterol is essential for proper signal transduction of the hedgehog family of proteins, key regulators of both developmental biology and tumor progression. We show that hedgehog signaling is diminished in our rudolph mutant. Our conclusions from studying this mouse mutant support two recent hypotheses in developmental biology. First, several human malformation syndromes are known to be caused by defects in cholesterol metabolism, but support linking the malformation to abnormal hedgehog signaling has not definitively been made. Second, while in vitro studies have shown that proper levels of metabolic by-products of cholesterol are necessary for proper hedgehog signaling, our studies offer the strongest genetic animal model evidence to support this idea.

A novel X-linked multiple congenital anomaly syndrome associated with an EBP mutation

Mutations of the gene coding for emopamil binding protein (EBP) can lead to deficient activity of 3-β-hydroxysteroid Δ(8), Δ(7) isomerase and are most commonly identified in. association with the X-linked dominant (male lethal) chondrodysplasia punctata (CDPX2), also known as Conradi-Hunermann syndrome. Our group has identified a hemizygous EBP mutation in males with a phenotype remarkable for Dandy-Walker malformation, cataracts, collodion skin and cryptorchidism. Additional findings of hydrocephalus, dysplasia of the corpus callosum, cardiovascular, craniofacial and skeletal anomalies were regularly seen in affected males and the family histories were supportive of an X-linked -recessive condition. The regularly reproducible constellation of cardinal features aligns very nicely with other disorders of sterol biosynthesis and is further distinguished by an absence of arty clinical manifestations in obligate carrier females. Biochemical analysis of blood from cases demonstrated markedly increased levels of 8(9)-cholestenol, and 8-dehydroeholesterol and a mildly increased level of 7-dehydrocholesterol; a similar pattern to what is seen in CDPX2. Sequence analysis of EJJP revealed a novel hemizygous missense mutation at position 141, predictive of a tryptophan to cysteine substitution (c.141G>T, p.W47C). The unaffected mothers were heterozygous for the c.141G>T mutation arid showed random X-inactivation pattern upon.

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.

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.

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.

Two novel frameshift mutations of the EBP gene in two unrelated Thai girls with Conradi-Hunermann-Happle syndrome

Conradi-Hünermann-Happle syndrome, also known as X-linked dominant chondrodysplasia punctata (CDPX2), is characterized by skeletal abnormalities, cutaneous anomalies and cataracts. CDPX2 is caused by mutations in the emopamil-binding protein (EBP). We report two unrelated Thai female patients with clinically typical CDPX2, in which we discovered two novel and de novo frameshift mutations: 506-507delAG and 540-541delCC. This study demonstrates that EBP is the gene responsible for CDPX2 across different populations and extends the total number of confirmed mutations to 55.

Avances biomoleculares en los trastornos epidérmicos hereditarios

In recent years, the genes responsible for many hereditary skin diseases have been discovered. These genes encode different proteins that participate in the terminal differentiation of the epidermis, so their alteration or absence causes a keratinization disorder and/or an increase in skin fragility. Thanks to genetic analyses, we have been able to understand the physiopathology of numerous genodermatoses and we have become closer to diagnosing many others. In the not-too-distant future, biomolecular techniques may foreseeably help us prevent and treat these processes, which include skin diseases as serious as epidermolysis bullosa or epidermolytic hyperkeratosis. In this article, we will study the most recent biomolecular findings referring to keratinization and epidermal disorders, mentioning the altered genes and/ or the defective proteins that cause them.

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.