Smith-Lemli-Opitz (RSH) syndrome bibliography: 1964-1993

Cholesterol and Phosphoinositides in Cilia Biology

Cilia are evolutionarily conserved organelles that can be found on virtually every cell. They appear as hair-like structures emanating from the cellular surface either as single or as bundles of cilia. There, they sense external stimuli and translate them into intracellular signals. Motile cilia beat for the generation of locomotion of unicellular organisms or fluid flow in certain body cavities of vertebrate organisms. Defects in cilia are detrimental and account for the development of ciliopathies, one of the fastest-growing family of afflictions. In the past decade, membrane lipids, such as cholesterol and phosphoinositides, have emerged as essential elements in both the signal transduction via cilia and the building of cilia itself. Here, we summarize the current knowledge on the impact of cholesterol and phosphoinositides on cilium biology.

Genomics and autism spectrum disorder

PURPOSE

To present the current state of the evidence regarding translation of genetics (the study of single genes) and genomics (the study of all genes and gene-gene or gene-environment interactions) into health care of children with autism spectrum disorder (ASD).

METHODS

This article presents an overview of ASD as an international health challenge, the emerging science related to broad diagnostic criteria, and the role of the nurse in research, education, and practice.

FINDINGS

Much progress is being made in the understanding of genetics and genomics of ASD. Environmental factors are thought to contribute to the risk of developing ASD by interacting with a number of genes in different ways, thus suggesting causal heterogeneity. The rising identified prevalence of ASD, the changing diagnostic criteria for ASD, and the complexity of the core and associated features have made it difficult to define the ASD phenotype (observable behaviors that result from gene-environment interaction). Because early identification improves opportunities for intervention, researchers are looking for a useful biomarker to detect ASD. This search is complicated by the likelihood that there are multiple causes for multiple expressions that are defined as the autism spectrum.

CONCLUSIONS

To date, genetic and genomic research on ASD have underscored the complexity of the causes of ASD indicating that there are very complex genetic processes involved that are still not well understood.

CLINICAL RELEVANCE

Nurses will benefit from new knowledge related to early identification, diagnosis, and implications for the family to promote early intervention. Families who have a child with ASD will require nursing support for advocacy for optimal health outcomes.

Smith-Lemli-Opitz syndrome: phenotype, natural history, and epidemiology

Smith-Lemli-Opitz syndrome (SLOS) is a congenital multiple anomaly/intellectual disability syndrome caused by a deficiency of cholesterol synthesis resulting from a deficiency of 7-dehydrocholesterol (7DHC) reductase encoded by DHCR7. SLOS is inherited in an autosomal recessive pattern. It is characterized by prenatal and postnatal growth retardation, microcephaly, a variable degree of intellectual disability that encompasses normal intelligence to severe intellectual deficiency, and multiple major and minor malformations. External malformations include distinctive facial features, cleft palate, postaxial polydactyly, 2-3 syndactyly of the toes, and underdeveloped external genitalia in males, while internal anomalies may affect every organ system. The clinical spectrum is wide, and rare individuals have been described with normal development and only minor malformations. The clinical diagnosis of SLOS is confirmed by demonstrating an abnormally elevated concentration of the cholesterol precursor, 7DHC, in serum or other tissues, or by the presence of two DHCR7 mutations. The enzymatic deficiency results in decreased cholesterol and increased 7DHC levels, both during embryonic development and after birth. The malformations found in SLOS may result from decreased cholesterol, increased 7DHC or a combination of these two factors. This review discusses the physical and behavioral phenotype of SLOS, the diagnostic approaches, the natural history from the prenatal period to adulthood, and current understanding of the pathophysiology of SLOS.

Recent advances in hedgehog signalling

Hedgehog (HH) proteins are an important class of secreted intercellular signals. The HH signal-transduction pathway is not fully understood, but a number of novel features have been elucidated recently. It is now clear that, during processing to generate an active signal, Drosophila HH proteins become covalently linked to cholesterol and are thereby largely tethered to the cell surface. HH signalling could therefore be affected by cholesterol metabolism. In addition, the pathway downstream of receptor binding involves a unique signalling complex containing the transcription factor CUBITUS INTERRUPTUS (CI), which becomes dissociated from microtubules in response to HH. This review discusses these new findings and their implications for HH signalling.

Tissue-limited mosaicism for monosomy 13

Karyotypic discordance between different tissues in an individual is uncommon. We report on a patient with multiple congenital anomalies and mosaicism for monosomy 13 limited to fibroblasts. Findings include microcephaly, agenesis of the corpus callosum, bilateral posterior colobomas, cataract and optic nerve dysplasia, patent foramen ovale, renal hypoplasia, hypospadias and unilateral inguinal hernia, unilateral hypoplasia of the lower limb, sparse and patchy hair, subtle pigmentary mosaicism, and global developmental delay. The lymphocyte karyotype was normal, whereas the fibroblast karyotype showed mosaicism for a del(13)(q11→ter). Review of the literature identified three previous reports of similar patients with multiple congenital anomalies, normal lymphocyte karyotype, and subsequent, diagnostic fibroblast karyotyping. Comparison of the previously reported patients with the patient reported here defines a common phenotype for tissue-limited mosaicism for monosomy 13 consisting of prenatal-onset growth deficiency; microcephaly; facial abnormalities including prominent nasal bridge, hypertelorism, ptosis, epicanthal folds, microphthalmia, coloboma, retinoblastoma, prominent maxilla, micrognathia, and low-set ears; limb abnormalities including small to absent thumbs, clinodactyly of fifth finger, fused metacarpal bones 4 and 5, talipes equinovarus, and short first toe; cardiac defect; renal anomalies; and genitalia abnormalities including hypospadias and cryptorchidism. In conclusion, this case further emphasizes that fibroblast karyotyping should be employed when the diagnosis remains unclear, especially in the presence of pigmentary mosaicism or segmental hypoplasia.

Sonic hedgehog ligand partners with caveolin-1 for intracellular transport

Prenatal alcohol exposure is the most common environmental factor leading to congenital birth defects in the United States. Although significant progress has been made in this field, the detailed molecular pathology of fetal alcohol syndrome (FAS) remains to be determined. Previously, we have shown that alcohol exposure perturbs hedgehog signal transduction in zebrafish embryos by inhibiting the post-translational cholesterol modification of Sonic hedgehog (Shh), leading to decreased levels of mature Shh ligand that is associated with the plasma membrane, and causing transient loss of Hh signaling, resulting in permanent FAS-related morphological abnormalities. In the present study, we further elucidate the mechanisms that regulate the intracellular transportation and secretion of Shh using the hepatic stellate cell line HSC8B. We have found that Shh is associated with caveolin-1 in the Golgi apparatus to form protein complexes and that these complexes are packaged as large punctuate structures (transport vesicles) that are transported to the plasma membrane in lipid raft microdomains. Alcohol exposure does not significantly interrupt translation of shh mRNA in endoplasmic reticulum (ER) or the trafficking of Shh from the ER to the Golgi apparatus. However, alcohol does prevent the entry of Shh into transport vesicles from the Golgi to the plasma membrane and specifically decreases the amount of caveolin-1/Shh complex found in lipid rafts, causing cytoplasmic accumulation of Shh and leading to a deficiency of Shh ligand secretion into the extracellular matrix.

Postmortem findings in term neonates

Neonatal deaths in infants born at term are relatively rare in the USA, occurring in 0.9/1000 live births. Congenital malformations, perinatal asphyxia, infections and inborn errors of metabolism are the leading causes. Chromosomal malformation syndromes, congenital heart disease, pulmonary hypoplasia and severe neural tube defects comprise the majority of lethal malformations. Several skeletal dysplasias are lethal in the newborn infant. Group B Streptococcus still plays a major role in neonatal mortality while deaths due to other infectious agents have decreased. Hypoxic ischaemic encephalopathy is a significant cause of neonatal death. Inborn errors of metabolism have variable presentations but some, such as the fatty acid oxidation disorders, may present in neonates and cause sudden death.

High doses of simvastatin, pravastatin, and cholesterol reduce brain cholesterol synthesis in guinea pigs

Recent epidemiological studies suggest that inhibitors of 3-hydroxy-3-methyl-glutaryl CoA reductase, so-called statins, are effective in lowering the prevalence of Alzheimer's disease. Whether the effect of statins is due to a local inhibition of cholesterol synthesis in the brain or whether it is mediated by the reduced levels of cholesterol in the circulation is not known. In the present work, we tested the possibility that high doses of lipophilic and hydrophilic statins, simvastatin and pravastatin, respectively, or a diet high in cholesterol could affect cholesterol homeostasis in the brain of guinea pigs. The total brain cholesterol levels were not affected by high-dose simvastatin or pravastatin treatment. Significantly lower levels of the cholesterol precursor lathosterol and its ratio to cholesterol were found in the brains of simvastatin and pravastatin-treated animals. 24S-Hydroxycholesterol, the transportable form of cholesterol across the blood-brain barrier, was significantly lower in the brain of pravastatin-treated animals. Excessive cholesterol feeding resulted in higher serum cholesterol levels but did not affect total brain cholesterol level. However, de novo cholesterol synthesis in the brain seemed to be down-regulated, as indicated by lower absolute levels and cholesterol-related ratios of lathosterol compared with controls. The passage of deuterium-labeled cholesterol across the blood-brain barrier in one animal was found to be approximately 1%. Our results suggest that brain cholesterol synthesis in guinea pigs can be slightly, but significantly, influenced by high doses of lipophilic and hydrophilic statins as well as by high dietary cholesterol intake, while total brain cholesterol content and thus, cholesterol homeostasis is maintained.

Smith-Lemli-Opitz syndrome: a review, case report and dental implications

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive developmental disorder characterized by multiple congenital malformations, dysmorphic craniofacial features, and mental impairment. SLOS is caused by a deficiency of the enzyme 7-dehydrocholesterol delta7 reductase which converts 7-dehyrocholesterol to cholesterol. This error results in elevated serum levels of 7-dehydrocholesterol and decreased levels of serum cholesterol. This article describes the clinical features and medical treatment of SLOS. A case report is included, with recommended guidelines for providing safe and comprehensive dental care for individuals with SLOS.

Molecular cloning and structural analysis of human sterol C5 desaturase

Sterol C5 desaturase (SC5D) converts lathosterol to 7-dehydrocholesterol in cholesterol biosynthesis. In this study, we investigated the genome structure of SC5D and transcription of the human SC5D gene to try to elucidate the mechanism by which cholesterol synthesis is regulated. The SC5D gene had a structural gene from a single copy from genome DNA that contained five exons and four introns. The human SC5D was found to be located in chromosome 11q24.2-24.3 by fluorescence in situ hybridization mapping. Human SC5D mRNA transcripts, of which the major transcript was a 2 kb and the minor transcripts were 8 kb and 1.4 kb mRNA transcripts, were detected in almost all of the tissues examined. The human SC5D gene contained a GC box instead of a TATA box upstream of the transcript start sites. Human SC5D transcription started from several transcription start sites, and the first start site was located 31 bp upstream of the translation start site (ATG). The expression level of SC5D mRNA extracted from human liver carcinoma cells decreased as the amount of cholesterol added to the culture medium was increased. Inhibition of SC5D transcription was ascribed to the suppression of promoter activity of SC5D.

Direct analysis of filter paper blood specimens for identification of Smith-Lemli-Opitz syndrome using time-of-flight secondary ion mass spectrometry

In this study, time-of-flight secondary ion mass spectrometry was used to distinguish between blood of normal infants and that of individuals with Smith-Lemli-Opitz (SLO) syndrome. SLO syndrome results in an abnormally low concentration of blood cholesterol and an elevated concentration of 7-dehydrocholesterol. Blood was spotted on filter paper and analyzed directly with no extractions or separations. Results showed that using ratios of fragment ions for cholesterol/dehydrocholesterol, patients with SLO and normal individuals could be unambiguously distinguished. Unknown samples from 28 individuals were obtained and identified correctly.

Pathogenesis of malformations in a rodent model for Smith-Lemli-Opitz syndrome

The fact that Smith-Lemli-Opitz syndrome (SLOS), a syndrome comprising major malformations involving a number of organ systems, results from an abnormality in cholesterol biosynthesis, was discovered only recently. Utilizing a drug (BM 15.766) to inhibit the same step in cholesterol biosynthesis as is abnormal in those affected with SLOS, we have developed a rat model that presents with abnormalities observed as early as gestational day 12 that appear to be consistent with some of those subsequent malformations that comprise the human syndrome. Abnormalities of the brain and face include deficiency in the midline region of the upper face, narrowing of the forebrain hemispheres and of the cerebral aqueduct, and deficiency in the developing lower jaw. Associated pathogenesis, as observed on gestational day 11 in histological sections and with scanning electron microscopy, involves abnormal cell populations at the rim of the developing forebrain and in the alar plate of the lower midbrain and hind-brain. The affected cells appear abnormally rounded up, having apparently lost their normal cell contacts. The potential basis for the selective vulnerability of this cell population and the impact of its vulnerability relative to subsequent dysmorphogenesis is discussed.

Cholesterol metabolism in the RSH/Smith-Lemli-Opitz syndrome: summary of an NICHD conference

During the evolution of multicellularity and attendant processes of development, cholesterol played a key role in the formation of the plasma membrane and outer mitochondrial membrane of every cell in the organism. Later functions include pivotal involvement in steroid, bile acid, and vitamin D metabolism and myelination of the nervous system. In the CNS myelination does not begin until the third trimester, and subcortical myelination not until after birth. The cholesterol of the cell membrane of the ovum is maternally derived. It is not known when the zygote begins making its own cholesterol during morphogenesis and histogenesis, but it must occur early to keep up with the dramatic rate of cell division in the embryo. Thus, it is a startling surprise that human embryos and fetuses apparently able to synthesize little cholesterol (because of a presumed defect of the delta 5,7-sterol, delta 7-reductase that converts 7-dehydrocholesterol (7-DHC) into cholesterol) frequently live to term and, rarely, may be so mildly affected as to attend school with only mild MR. The discovery by G. Stephen Tint and his co-workers of the apparent 7-DHC reductase deficiency makes the RSH (Smith-Lemli-Opitz) syndrome the first true metabolic malformation syndrome. A teratological animal model which has been known for 30 years now appears applicable to the RSH/SLO syndrome. A multidisciplinary NICHD conference held on September 20-21, 1993 reviewed the numerous implications of this discovery and agreed unanimously that research in this field be given highest priority in order to better understand cholesterol synthesis in the mammalian brain, cholesterol transport from mother to embryo and fetus, pre- and postnatal metabolic compensation in structure and function for a profound block in cholesterol synthesis, the nature of the blood-brain barrier for cholesterol, treatment of affected infants, children, and adults, structure and genetic specification of a 7-DHC reductase enzyme (which has never been purified!) and its evolution, the variability of the syndrome and whether it is genetically homo- or heterogeneous, the population genetics of the RSH syndrome, possible selective advantages (or disadvantages) of heterozygotes, and means of newborn screening, carrier detection, and prenatal diagnosis.