Defect In Cholesterol Biosynthesis Research Articles

Cataract Development in a Young Patient with Lathosterolosis: A Clinicopathologic Case Report

To report a unique case of cataract in a young patient with lathosterolosis, a singular defect of cholesterol biosynthesis, and to report the clinical results and histopathologic findings after cataract surgery. A 7-year-old patient with lathosterolosis, a rare defect of cholesterol biosynthesis, presented with a complex phenotype, including severe mental retardation, liver disease, multiple congenital anomalies, and bilateral posterior subcapsular cataracts. After a severe metabolic decompensation, a worsening in the lens opacity of the left eye occurred. The authors thus performed cataract surgery and made a histopathologic analysis of aspirated lenticular samples. The following examinations were performed at 1 day, 1 week, 3 months, 6 months, 12 months, and 24 months: refraction, biomicroscopy, and fundus evaluation. Visual acuity was not assessable due to lack of patient collaboration. The postoperative follow-up period was 24 months. Histopathologic findings on lenticular fragments revealed the presence of fibers disposed in a honeycomb, samples with homogeneous eosinophilic lens fibers, and other fragments characterized by bulgy elements referable to cortical fibers with degenerative characteristics. After surgery, biomicroscopic evaluation revealed no significant inflammation and good intraocular lens centration at the various control visits. No intraoperative or postoperative complications occurred. No posterior capsule opacification occurred 2 years after surgery. Lathosterolosis may lead to dysmetabolic cataract development; this unique case of cataract in such a patient has been successfully managed with surgery. Clinical results were excellent, and no complications occurred either intra- or postoperatively.

Pathologic, radiographic and molecular findings in three fetuses diagnosed with HEM/Greenberg skeletal dysplasia

Greenberg skeletal dysplasia is a very rare, autosomal recessive, in utero, lethal chondrodystrophy for which only eight index cases of diverse ethnic origin have been reported so far. The defect is associated with a defect in cholesterol biosynthesis and due to mutations in the gene encoding the lamin B receptor (LBR). A familial case of three fetuses of a consanguineous Greek couple is presented including prenatal, physical, radiographic, histopathologic, and molecular genetic findings. The tentative diagnosis of Greenberg skeletal dysplasia based on pathological findings was confirmed by the identification of a homozygous, N547D amino acid substitution in the LBR gene in the third affected fetus. The present case represents the ninth described case of Greenberg dysplasia and the second case of Greek origin. The characteristic 'moth-eaten' radiographic appearance is already seen at 13 weeks' gestational age.

DHCR7 mutations causing the Smith—Lemli—Opitz syndrome

The Smith—Lemli—Opitz Syndrome (SLOS) is a metabolic malformation and mentalretardation syndrome that is casued by a defect in cholesterol biosynthesis. The resultingloss of cholesterol leads to a spectrum from mild to very severe phenotype. The DHCR7 geneencodes Ä7 sterol reductase, the enzyme catalyzing the reduction of 7-dehydrocholesterolto cholesterol. This review provides an overview of knowledge about mutations leading toSLOS. It describes why and how age and origin of mutations are estimated. It demonstratesthat mutational spectra are population specific and that so-called null mutations have ahigh carrier frequency, probably not due to selection alone. Finally, a correlation betweenDHCR7 genotype and SLOS phenotype and a genetic modifying factor for this diseaseis described.

Identification of a Novel DHCR7 Mutation in a Korean Patient With Smith-Lemli-Opitz Syndrome

Smith-Lemli-Opitz syndrome is a unique malformation syndrome characterized by a defect in cholesterol biosynthesis, which is very rare among populations in Middle and East Asia. The authors identified compound heterozygous mutations ([p.Arg352Trp] + [p.Lys376ArgfsX37]) in a Korean girl with clinical and laboratory features typical of Smith-Lemli-Opitz syndrome. The Lys376ArgfsX37 mutation is a novel mutation, and to the best of the authors' knowledge, this is the first report of a clinically and genetically confirmed case of Smith-Lemli-Opitz syndrome in Korea.

Clinical phenotype of lathosterolosis

Lathosterolosis (LS) is a defect of cholesterol biosynthesis due to the deficiency of the enzyme sterol-C5-desaturase. Only two patients have been described to date, both presenting with multiple malformations, mental retardation, and liver involvement. In addition in one of them pathological examination revealed mucolipidosis-like inclusions on optic microscopy analysis, and peculiar lysosomal lamellar bodies on electron microscopy analysis. This study is focused on a better characterization of the clinical phenotype of LS. We describe a further case in a fetus, sibling of the first patient reported, presenting with neural tube defect, craniofacial and limb anomalies, and prenatal liver involvement. The fetal phenotype suggests the possible occurrence of significant intrafamilial variability in LS, and expands the phenotypic spectrum of the disease. Histological examination of autopsy samples from the fetus and skin fibroblasts from the living sibling suggested that the mucolipidosis-like picture previously reported is not a constant feature of LS, being possibly associated with the most severe biochemical defects, but confirmed the ultrastructural finding of lamellar inclusions. The LS phenotype appears to be characterized by the distinctive association of a recognizable pattern of congenital anomalies, involving axial and appendicular skeleton, liver, central nervous and urogenital systems, and lysosomal storage. This condition partially overlaps with other defects of sterol metabolism, suggesting intriguing pathogenic links among these conditions.

Sensorineural hearing-loss in the Smith–Lemli-Opitz syndrome

Summary The Smith–Lemli-Opitz (SLO) syndrome is an autosomal recessive disorder caused by a mutation in the 7-dehydrocholesterol reductase gene, which in turn provokes a defect in cholesterol biosynthesis. SLO is characterised by a specific physical, behavioural and developmental pattern, and the main clinical features include minor facial anomalies, multiple congenital anomalies, failure to thrive and mental retardation. This report describes a case in a newborn child with the typical clinical signs and symptoms of SLO syndrome, who was also affected by profound bilateral sensorineural deafness, and revises the literature suggesting that audiological examination of patients with SLO syndrome may be useful.

Partial Rescue of Retinal Function and Sterol Steady-State in a Rat Model of Smith-Lemli-Opitz Syndrome

The Smith-Lemli-Opitz syndrome (SLOS) is the first-described in a growing family of hereditary defects in cholesterol biosynthesis, and presents with a spectrum of serious abnormalities, including multiple dysmorphologies, failure to thrive, cognitive and behavioral impairments, and retinopathy. Using a pharmacologically induced rat model of SLOS that exhibits key hallmarks of the disease, including progressive retinal degeneration and dysfunction, we show that a high-cholesterol diet can substantially correct abnormalities in retinal sterol composition, with concomitant improvement of visual function, particularly within the cone pathway. Although histologic degeneration still occurred, a high-cholesterol diet reduced the number of pyknotic photoreceptor nuclei, relative to animals on a cholesterol-free diet. These findings demonstrate that cholesterol readily crosses the blood-retina barrier (unlike the blood-brain barrier) and suggest that cholesterol supplementation may be efficacious in treating SLOS-associated retinopathy.

Abnormal sterol metabolism in holoprosencephaly: studies in cultured lymphoblasts

Background: Holoprosencephaly (HPE) is the most common structural malformation of the developing forebrain in humans. The aetiology is heterogeneous and remains unexplained in approximately 75% of patients. Objective: To examine...

Loss of apolipoprotein E exacerbates the neonatal lethality of the Smith-Lemli-Opitz syndrome mouse

The Smith-Lemli-Opitz syndrome (SLOS) is caused by a genetic defect in cholesterol biosynthesis; mutations in the enzyme 3ß-hydroxysterol Δ7 reductase (Dhcr7) lead to a failure of cholesterol (and desmosterol) synthesis, with an accumulation of precursor sterols, such as 7-dehydrocholesterol. Extensive genotype–phenotype analyses have indicated that there is considerable variation in the severity of the disease, much of which is not explained by defects in the Dhcr7 gene alone. Factors ranging from variations in maternal–fetal cholesterol transfer during pregnancy, to other genetic factors have been proposed to account for this variability. Variations at the APOE locus affect plasma cholesterol levels in humans and this polymorphic gene has been found to be associated with cardiovascular as well as neurological disorders. This locus has recently been implicated in accounting for some of the variations in SLOS. To address whether maternal hypercholesterolemia can affect fetal outcome, we tested the ability of maternal hypercholesterolemia to rescue the neonatal lethality in a mouse model of SLOS. Maternal hypercholesterolemia, induced by ApoE or Ldl-r deficiency not only failed to ameliorate the postnatal lethality, it increased the prenatal mortality of Dhcr7 deficient pups. Thus the murine data suggest that maternal loss of ApoE or Ldl-r function further exacerbates the neonatal lethality, suggesting they may play a role in maternal transfer of cholesterol to the embryo.

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.

Loose lipid rafts lead to trigger-happy mast cells

Mast cells that accumulate cholesterol precursors in their membranes tend to overreact, according to Kovarova and colleagues on page 1161. This mast cell hyperresponsiveness might help explain why patients with a genetic disease known as Smith-Lemli-Opitz syndrome (SLOS) are prone to food allergies. Figure 1 Degranulation is enhanced in mast cells lacking the enzyme that reduces 7-dehydrocholesterol (DHCR KO). Patients with SLOS have abnormally low levels of circulating cholesterol—and a corresponding abundance of the cholesterol precursor 7-dehydrocholesterol (DHC)—due to defects in the gene that encodes the DHC-reducing enzyme (DHCR7). This cholesterol deficiency causes a bevy of developmental defects, consistent with the known requirement for cholesterol during embryonic development. But the allergic manifestations of SLOS are poorly understood. Kovarova and colleagues suspected that mast cells—the principle allergy-triggering cell type—might be involved, as mast cells rely on the proper distribution of cholesterol-rich lipid rafts in their membranes for appropriate activation and deactivation. Their hunch was right. Mast cells from Dhcr7-deficient mice were hyperactive compared with wild-type cells, as measured by increased degranulation and proinflammatory cytokine production upon activation. But to their surprise, the deficient cells had normal numbers of lipid rafts—although the abundance of DHC and paucity of cholesterol made the rafts less stable than normal. The destabilized rafts contained fewer molecules of the kinase Lyn, leading to a decrease in the Lyn-dependent activation of Csk-binding protein, a negative regulator of the degranulation-stimulating kinase Fyn. Depleting wild-type cells of cholesterol had the same activation-enhancing effect, which was reversed when cholesterol was added back. But adding cholesterol to the Dhcr7-deficient cells had minimal effect, suggesting that the activation defect was caused by the accumulation of DHC, rather than the depletion of cholesterol. These results suggest that patients with other diseases involving defects in cholesterol biosynthesis might be more prone to allergies—a possibility that remains to be tested.

A Case of Smith-Lemli-Opitz Syndrome, Defect of Cholesterol Biosynthesis

We report the case of a child with Smith-Lemli-Opitz Syndrome. The pregnancy was complicated by prenatal growth retardation. The baby was admitted to the Neonatal Intensive Care Unit of Chieti when she was five months old. She showed postnatal growth retardation, trouble sucking and swallowing, microcephaly and multiple major and minor malformations, including characteristic facial features and 2-3 syndactyly of the toes. We found correlations between multiple congenital malformations, failure to thrive and low plasmatic cholesterol measurement.

Male Pseudohermaphroditism Caused by an Inborn Error in Cholesterol Biosynthesis: Smith-Lemli-Opitz Syndrome

Smith-Lemli-Opitz syndrome is an autosomal recessive disorder caused by mutations of 3? -hydroxysterol –? 7reductase gene (DHCR7) which maps to 11q12-13 and was the first discovered defect in cholesterol biosynthesis resulting in a congenital dysmorphology syndrome. We present the case of a 46,XY newborn with ambiguous genitalia and multiple congenital anomalies (atrial septal defect, ventricular septal defect, syndactyly of the second and third toe, cleft palate, webbed neck, small fontanels, mesomelia, simian palmar crease, micrognathia, wide nasal bridge with anteverted nostrils, low set ears). Hormonal assessment performed at twelve days revealed a decreased testosterone level (0.03 ng/mL), a high estradiol level (448.8 pg/mL), normal LH (2.8UI/mL), DHEAS (86.61ig/dL), progesterone (1.34ng/mL) and 17 hydroxyprogesterone (1.08ng/mL) levels. Cholesterol was low (44mg/dL) confirming the diagnostic of Smith-Lemli-Opitz syndrome.

Lipid hydroperoxide formation in the retina: correlation with retinal degeneration and light damage in a rat model of Smith–Lemli–Opitz syndrome

The Smith–Lemli–Opitz syndrome (SLOS) is an autosomal recessive disease presenting with multiple congenital anomalies, caused by a defect in cholesterol biosynthesis that results in abnormally elevated levels of 7-dehydrocholesterol (7DHC). Progressive retinal degeneration has been demonstrated in a rat model of SLOS, which is markedly exacerbated by intense light, far more so than occurs in normal albino rats under the same conditions. Herein, we demonstrate that, by six postnatal weeks, retinas in the SLOS rat model contain levels of lipid hydroperoxides (LPOs) comparable to those found in light-damaged albino rats (twice the normal steady-state levels), and that intense light exposure results in a three-fold elevation of LPOs with concomitant severe retinal degeneration. These results suggest a correlation between retinal degeneration and LPO levels. We propose that the presence of 7DHC in the SLOS rat retina potentiates LPO formation, and promotes the observed hypersensitivity to light-induced retinal degeneration.

Congenital brain anomalies in distal cholesterol biosynthesis defects

Cholesterol is known to be a significant constituent of the central nervous system. It also plays an important role in developmental pathways to form the human brain, such as the Sonic Hedgehog pathway. Disturbances in the formation of cholesterol may therefore be expected to cause brain malformations and brain dysfunctions. Here a short review of the consequences of defects of the distal cholesterol pathways to brain formation and functioning is provided.

Cytochrome P450 17α Hydroxylase/17,20 Lyase (CYP17) Function in Cholesterol Biosynthesis: Identification of Squalene Monooxygenase (Epoxidase) Activity Associated with CYP17 in Leydig Cells

Cytochrome P450 17alpha-hydroxylase/17,20-lyase (CYP17) is a microsomal enzyme catalyzing two distinct activities, 17alpha-hydroxylase and 17,20-lyase, essential for the biosynthesis of adrenal and gonadal steroids. CYP17 is a potent oxidant, it is present in liver and nonsteroidogenic tissues, and it has been suggested to have catalytic properties distinct to its function in steroid metabolism. To identify CYP17 functions distinct of its 17alpha-hydroxylase/17,20-lyase activity, we used MA-10 mouse tumor Leydig cells known to be defective in 17alpha-hydroxylase/17,20-lyase activity. A CYP17 knocked down MA-10 clone (MA-10(CYP17KD)) was generated by homologous recombination and its steroidogenic capacity was compared with wild-type cells (MA-10(wt)). Although no differences in cell morphology and proliferation rates were observed between these cells, the human chorionic gonadotropin-induced progesterone formation and de novo synthesis of steroids were dramatically reduced in MA-10(CYP17KD) cells; their steroidogenic ability could be rescued in part by transfecting CYP17 DNA into the cells. Knocking down CYP17 mRNA by RNA interference yielded similar results. However, no significant difference was observed in the steroidogenic ability of cells treated with 22R-hydroxycholesterol, which suggested a defect in cholesterol biosynthesis. Incubation of MA-10(CYP17KD) cells with (14)C-labeled squalene resulted in the formation of reduced amounts of radiolabeled cholesterol compared with MA-10(wt) cells. In addition, treatment of MA-10(CYP17KD) cells with various cholesterol substrates indicated that unlike squalene, addition of squalene epoxide, lanosterol, zymosterol, and desmosterol could rescue the hormone-induced progesterone formation. Further in vitro studies demonstrated that expression of mouse CYP17 in bacteria resulted in the expression of squalene monooxygenase activity. In conclusion, these studies suggest that CYP17, in addition to its 17alpha-hydroxylase/17,20-lyase activity, critical in androgen formation, also expresses a secondary activity, squalene monooxygenase (epoxidase), of a well-established enzyme involved in cholesterol biosynthesis, which may become critical under certain conditions.

Characterization of liver involvement in defects of cholesterol biosynthesis: Long‐term follow‐up and review

Inborn defects of cholesterol biosynthesis are a group of metabolic disorders presenting with mental retardation and multiple congenital anomalies (MCA/MR syndromes). Functional and structural liver involvement has been reported as a rare (2.5-6%) complication of the Smith-Lemli-Opitz syndrome (SLOS) and it has not been fully characterized. Here, we report on a long-term follow-up study of four patients with SLOS, and one case with lathosterolosis who presented with liver disease and underwent an extensive diagnostic work-up. Reports of liver involvement in cholesterol biosynthesis defects are reviewed. Two main different patterns of liver involvement emerged: progressive cholestasis, and stable isolated hypertransaminasemia. In our series, the first pattern was found in two patients with SLOS and one with lathosterolosis, and the second in two SLOS cases. Cholestasis was associated with early lethality and normal serum gamma-glutamyl-transferase (GGT) levels in SLOS, while possible prolonged survival and high GGT levels were seen in lathosterolosis. Hepatic fibrosis was present in both conditions. Liver biopsy performed in one of our SLOS patients with isolated hypertransaminasemia, showed only mild hydropic degeneration of the hepatocytes. The presence of liver involvement in 16% of the SLOS patients diagnosed at our Center suggests that this complication might have been underestimated in previously reported cases, possibly overshadowed by the severity of multiple malformations. Fetal hepatopathy, cholestasis, and isolated hypertransaminasemia can occur also in other disorders of cholesterol biosynthesis, such as mevalonic aciduria, desmosterolosis, Conradi-Hunermann syndrome, Greenberg dysplasia, and Pelger-Huet homozygosity syndrome. This group of inherited disorders should be considered in the differential diagnosis of patients presenting with liver disease associated with developmental delay and/or multiple malformations. Periodic liver function evaluations are recommended in these patients.

MRI and 1H MRS findings in Smith-Lemli-Opitz syndrome.

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder characterized by a defect in cholesterol biosynthesis, associated with mental retardation and multisystem structural abnormalities. This study investigated the prevalence of congenital CNS abnormalities by MRI in a large series of patients with SLOS and the correlation of the clinical and biochemical findings with the results of MRI and 1H MRS. Eighteen patients were studied; all underwent MRI of the brain, and 16 had 1H MRS of the cerebral white matter. The ratios choline:NAA, lipid:NAA, and lipid:choline metabolite were found to be correlated with the clinical degree of disease severity, serum total sterol ratios (cholesterol/cholesterol + 7-dehydrocholesterol + 8-dehydrocholesterol) and in two cases with the effect of cholesterol therapy. Abnormal CNS findings were noted in five patients, including callosal abnormalities (n = 4), Dandy-Walker variant (n = 1), and arachnoid cyst (n = 1). Holoprosencephaly was noted in one patient with a prevalence of 6%. Choline:NAA was elevated in seven patients. There was a statistically significant positive correlation between the lipid:choline ratio and the serum cholesterol precursor, 8-dehydrocholesterol. In two patients 1H MRS demonstrated abnormally elevated lipids prior to cholesterol therapy, which improved on therapy. The use of MRI and 1H MRS is an effective way to demonstrate brain structural abnormalities in patients with SLOS and may prove to be an effective method for the assessment of the effects of cholesterol replacement therapy in the brain.

Smith-Lemli-Opitz syndrome and the DHCR7 gene.

Smith-Lemli-Opitz syndrome, a severe developmental disorder associated with multiple congenital anomalies, is caused by a defect of cholesterol biosynthesis. Low cholesterol and high concentrations of its direct precursor, 7-dehydrocholesterol, in plasma and tissues are the diagnostic biochemical hallmarks of the syndrome. The plasma sterol concentrations correlate with severity and disease outcome. Mutations in the DHCR7 gene lead to deficient activity of 7-dehydrocholesterol reductase (DHCR7), the final enzyme of the cholesterol biosynthetic pathway. The human DHCR7 gene is localised on chromosome 11q13 and its structure has been characterized. Ninety-one different mutations in the DHCR7 gene have been published to date. This paper is a review of the clinical, biochemical and molecular genetic aspects.

Lathosterolosis, a Novel Multiple-Malformation/Mental Retardation Syndrome Due to Deficiency of 3β-Hydroxysteroid-Δ 5-Desaturase

We report the clinical, biochemical, and molecular characterization of a patient with a novel defect of cholesterol biosynthesis. This patient presented with a complex phenotype, including multiple congenital anomalies, mental retardation, and liver disease. In the patient's plasma and cells, we found increased levels of lathosterol. The biosynthesis of cholesterol in the patient's fibroblasts was defective, showing a block in the conversion of lathosterol into 7-dehydrocholesterol. The activity of 3beta-hydroxysteroid-Delta(5)-desaturase (SC5D), the enzyme involved in this reaction, was deficient in the patient's fibroblasts. Sequence analysis of the SC5D gene in the patient's DNA, showing the presence of two missense mutations (R29Q and G211D), confirmed that the patient is affected by a novel defect of cholesterol biosynthesis.