R352Q mutation of the DHCR7 gene is common among Japanese Smith-Lemli-Opitz syndrome patients

The Intimate Connection Between Lipids and Hedgehog Signaling

Hedgehog (HH) signaling is an intercellular communication pathway involved in directing the development and homeostasis of metazoans. HH signaling depends on lipids that covalently modify HH proteins and participate in signal transduction downstream. In many animals, the HH pathway requires the primary cilium, an organelle with a specialized protein and lipid composition. Here, we review the intimate connection between HH signaling and lipids. We highlight how lipids in the primary cilium can create a specialized microenvironment to facilitate signaling, and how HH and components of the HH signal transduction pathway use lipids to communicate between cells.

Ciliary membrane, localised lipid modification and cilia function

Cilium, a tiny microtubule-based cellular appendage critical for cell signalling and physiology, displays a large variety of receptors. The composition and turnover of ciliary lipids and receptors determine cell behaviour. Due to the exclusion of ribosomal machinery and limited membrane area, a cilium needs adaptive logistics to actively reconstitute the lipid and receptor compositions during development and differentiation. How is this dynamicity generated? Here, we examine whether, along with the Intraflagellar-Transport, targeted changes in sector-wise lipid composition could control the receptor localisation and functions in the cilia. We discuss how an interplay between ciliary lipid composition, localised lipid modification, and receptor function could contribute to cilia growth and signalling. We argue that lipid modification at the cell-cilium interface could generate an added thrust for a selective exchange of membrane lipids and the transmembrane and membrane-associated proteins.

Carrier frequency and incidence estimation of Smith-Lemli-Opitz syndrome in East Asian populations by Genome Aggregation Database (gnomAD) based analysis

Background

Smith–Lemli–Opitz syndrome (SLOS) is an autosomal, recessively inherited congenital malformation syndrome characterized by multiple congenital anomalies such as microcephaly with mental defects, distinctive facial features, genital abnormalities, and 2–3 syndactyly of the toes. SLOS is caused by defective 7-dehydrocholesterol reductase, which is encoded by the DHCR7 gene. This study aimed to analyze the carrier frequency and expected incidence of SLOS in East Asians and Koreans using exome data from the Genome Aggregation Database (gnomAD) through the 2015 American College of Medical Genetics and Genomics and the Association for Molecular Pathology guideline (2015 ACMG-AMP guideline).

Methods

We analyzed 9197 exomes for East Asian populations from gnomAD, comprising 1909 Korean, 76 Japanese, and 7212 other East Asian populations. All identified variants were classified according to the 2015 ACMG-AMP guideline.

Results

According to the 2015 ACMG-AMP guideline, 15 pathogenic variant/likely pathogenic variant (PV/LPV) cases were identified in 33 East Asian individuals (33/9191 = 0.4%). Among them, four PVs/LPVs were identified in 19 Korean individuals (19/1909 = 1.0%). The predicted incidence, based upon the carrier rates of PV/LPV of DHCR7 alleles, is 1 in 310,688 in East Asians and l in 40,380 in Koreans.

Conclusions

This study is the first to identify carrier frequencies in East Asians and Koreans using gnomAD. It was confirmed that East Asians (0.4%) had a lower carrier frequency than did other ethnicities (1–3%) and Koreans (1.0%) had similar or lower carrier frequencies than other ethnicities. The variant spectrums of DHCR7 in East Asian and Korean populations differed greatly from those of other ethnic groups.

Insufficiency of ciliary cholesterol in hereditary Zellweger syndrome

Primary cilia are antenna‐like organelles on the surface of most mammalian cells that receive sonic hedgehog (Shh) signaling in embryogenesis and carcinogenesis. Cellular cholesterol functions as a direct activator of a seven‐transmembrane oncoprotein called Smoothened (Smo) and thereby induces Smo accumulation on the ciliary membrane where it transduces the Shh signal. However, how cholesterol is supplied to the ciliary membrane remains unclear. Here, we report that peroxisomes are essential for the transport of cholesterol into the ciliary membrane. Zellweger syndrome (ZS) is a peroxisome‐deficient hereditary disorder with several ciliopathy‐related features and cells from these patients showed a reduced cholesterol level in the ciliary membrane. Reverse genetics approaches revealed that the GTP exchange factor Rabin8, the Rab GTPase Rab10, and the microtubule minus‐end‐directed kinesin KIFC3 form a peroxisome‐associated complex to control the movement of peroxisomes along microtubules, enabling communication between peroxisomes and ciliary pocket membranes. Our findings suggest that insufficient ciliary cholesterol levels may underlie ciliopathies.

Novel DHCR7 mutation in a case of Smith-Lemli-Opitz syndrome showing 46,XY disorder of sex development

Smith-Lemli-Opitz syndrome is an autosomal recessive disease caused by mutations in 7-dehydrocholesterol reductase (DHCR7), which is rarely observed in Japan. We report a Japanese case with 46,XY disorder of sex development and Y-shaped 2-3 toe syndactyly. DHCR7 gene analysis revealed compound heterozygous mutations including the novel mutation H442R. Early diagnosis led to starting cholesterol treatment at an early age.

Investigation of 7-dehydrocholesterol reductase pathway to elucidate off-target prenatal effects of pharmaceuticals: a systematic review

Mendelian diseases contain important biological information regarding developmental effects of gene mutations that can guide drug discovery and toxicity efforts. In this review, we focus on Smith–Lemli–Opitz syndrome (SLOS), a rare Mendelian disease characterized by compound heterozygous mutations in 7-dehydrocholesterol reductase (DHCR7) resulting in severe fetal deformities. We present a compilation of SLOS-inducing DHCR7 mutations and the geographic distribution of those mutations in healthy and diseased populations. We observed that several mutations thought to be disease causing occur in healthy populations, indicating an incomplete understanding of the condition and highlighting new research opportunities. We describe the functional environment around DHCR7, including pharmacological DHCR7 inhibitors and cholesterol and vitamin D synthesis. Using PubMed, we investigated the fetal outcomes following prenatal exposure to DHCR7 modulators. First-trimester exposure to DHCR7 inhibitors resulted in outcomes similar to those of known teratogens (50 vs 48% born-healthy). DHCR7 activity should be considered during drug development and prenatal toxicity assessment.

Pathogenesis, Epidemiology, Diagnosis and Clinical Aspects of Smith-Lemli-Opitz Syndrome

INTRODUCTION

Smith-Lemli-Opitz Syndrome (SLOS) is a malformation syndrome inherited in an autosomal recessive fashion. It is due to a metabolic defect in the conversion of 7-dehydrocholesterol to cholesterol, which leads to an accumulation of 7-dehydrocholesterol and frequently a deficiency of cholesterol. The syndrome is characterized by typical dysmorphic facial features, multiple malformations, and intellectual disability.

AREAS COVERED

In this paper we provide an overview of the clinical phenotype and discuss how the manifestations of the syndrome vary depending on the age of the patients. We then explore the underlying biochemical defect and pathophysiological alterations that may contribute to the many disease manifestations. Subsequently we explore the epidemiology and succinctly discuss population genetics as they relate to SLOS. The next section presents the diagnostic possibilities. Thereafter, the treatment and management as is standard of care are presented.

EXPERT OPINION

Even though the knowledge of the underlying molecular mutations and the biochemical alterations is being rapidly accumulated, there is currently no efficacious therapy addressing neurological dysfunction. We discuss the difficulty of treating this disorder, which manifests as a combination of a malformation syndrome and an inborn error of metabolism. A very important factor in developing new therapies is the need to rigorously establish efficacy in controlled trials.

Mutational spectrum of Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS; OMIM #270400) is an autosomal recessive malformation syndrome characterized by a large spectrum of morphogenic and congenital anomalies. SLOS is caused by mutations in the DHCR7 gene, which encodes 7-dehydrocholesterol reductase, the enzyme that catalyzes the final step in cholesterol biosynthesis. We report on 154 currently known mutations in DHCR7 identified in patients affected with SLOS and discuss their coding consequences. These 154 mutations include 130 missense, 8 nonsense, 8 deletions, 2 insertions, 1 indel, and 5 splice site mutations. Using information available from published case reports and from patients identified in our clinical diagnostic laboratory, we analyzed correlations between genotype, clinical presentation and 7-dehydrocholesterol level.

Adrenal function in Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is a multiple malformation syndrome due to mutations of the 7-dehydrocholesterol reductase gene (DHCR7), which leads to a deficiency of cholesterol synthesis and an accumulation of 7-dehydrocholesterol. The SLOS clinical spectrum ranges from multiple major malformations to a mild phenotype with minor anomalies and intellectual disability. Several children with SLOS and adrenal insufficiency have been described. We performed ovine corticotropin (oCRH) testing in 35 SLOS patients and 16 age- and gender-matched controls. We reviewed prior adrenocorticotropin (ACTH) stimulation tests of our SLOS patients (19 of 35 available) and reviewed results of ACTH stimulation tests from 10 additional SLOS patients. Results from oCRH testing showed that patients with SLOS had significantly higher ACTH baseline values than healthy controls (24.8 ± 15.3 pg/ml vs. 17.8 ± 7.5 pg/ml, P = 0.034). However, no statistically significant differences were noted for peak ACTH values (74.4 ± 35.0 pg/ml vs. 64.0 ± 24.9 pg/ml, P = 0.303) and for baseline (14.2 ± 7.8 mcg/dl vs. 14.2 ± 6.3 mcg/dl, P = 0.992) and peak cortisol values (28.2 ± 7.9 mcg/dl vs. 24.8 ± 8.1 mcg/dl, P = 0.156). The area-under-the-curve (AUC) was not significantly different in SLOS patients compared to controls for both ACTH (250.1 ± 118.7 pg/ml vs. 195.3 ± 96.6 pg/ml, P = 0.121) as well as cortisol secretion (83.1 ± 26.1 mcg/dl vs. 77.8 ± 25.9 mcg/dl, P = 0.499). ACTH stimulation test results were normal in 28 of 29 tests. The individual with the abnormal test results had subsequent normal oCRH tests. The slightly increased baseline ACTH level seen during oCRH testing may be due to compensated adrenocortical insufficiency. However, we were able to show that our patients with SLOS had an adequate glucocorticoid response, and thus, in mild to moderate cases of SLOS stress steroid coverage may not be warranted.

Smith-Lemli-Opitz syndrome among Arabs

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder of variable presentation caused by the deficiency of the 3β- hydroxycholesterol Δ(7) - reductase. Over the past 10 years, our biochemical laboratory has screened 191 plasma samples for possible SLOS, measuring the plasma cholesterol and 7-dehydrocholesterol using gas chromatography-mass spectrometry (GC-MS). The SLOS was confirmed in only five Arab patients with growth retardation, global developmental delay, dysmorphic features, and 2-3 toe syndactyly, among other findings. All cases represented moderate to severe form of SLOS. One patient had a unique cardiovascular malformation (cor triatriatum with significant obstruction of the right pulmonary veins). Two previously reported N287K (861 C>A) and R352Q (1055 G>A) and a novel R352L (1055 G>T) mutations were identified in the DHCR7 gene in these patients. The paper sheds light on this rare disease among Arabs and reviews all reported SLOS cases in the Arab population.

A novel DHCR7 mutation in a Smith-Lemli-Opitz syndrome infant presenting with neonatal cholestasis

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive malformation syndrome caused by a defect in cholesterol biosynthesis. The incidence is very low in Asians and only one case has been reported in Korea thus far. Recently, we found an infant with neonatal cholestasis. He had microcephaly, ambiguous genitalia, cleft palate, syndactyly of toes, patent ductus arteriosus and hypertrophic pyloric stenosis. The serum cholesterol was decreased and serum 7-dehydrocholesterol was markedly elevated. Genetic analysis of the DHCR7 gene identified a novel missense mutation (Pro227Ser) as well as a known mutation (Gly303Arg) previously identified in a Japanese patient with SLOS. Although rare in Korea, SLOS should be considered in the differential diagnosis of neonatal cholestasis, especially in patients with multiple congenital anomalies and low serum cholesterol levels.

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.