Syndrome of retardation with urogenital and skeletal anomalies (Smith-Lemli-Opitz syndrome): clinical features and mode of inheritance

Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive, multiple congenital malformation and intellectual disability syndrome, with clinical characteristics that encompass a wide spectrum and great variability. Elucidation of the biochemical and genetic basis for SLOS, specifically understanding SLOS as a cholesterol deficiency syndrome caused by mutation in DHCR7, opened up enormous possibilities for therapeutic intervention. When cholesterol was discovered to be the activator of sonic hedgehog, cholesterol deficiency with inactivation of this developmental patterning gene was thought to be the cause of SLOS malformations, yet this explanation is overly simplistic. Despite these important research breakthroughs, there is no proven treatment for SLOS. Better animal models are needed to allow potential treatment testing and the study of disease pathophysiology, which is incompletely understood. Creation of human cellular models, especially models of brain cells, would be useful, and in vivo human studies are also essential. Biomarker development will be crucial in facilitating clinical trials in this rare condition, because the clinical phenotype can change over many years. Additional research in these and other areas is critical if we are to make headway towards ameliorating the effects of this devastating condition.

Endocrine disorders in the neonate

There is a significant amount of knowledge that has been gained in recent years in the study of endocrine disorders in the newborn. The explosion of genetic data shedding light on the origins of endocrine disease has expanded the level of diagnostic evaluation and management of these infants. This article provides a general review of endocrine disorders as they present in a newborn.

The Smith-Lemli-Opitz syndrome: a novel metabolic way of understanding developmental biology, embryogenesis, and dysmorphology

The brief history of the Smith-Lemli-Opitz syndrome (SLOS) (MIM 270400) reflects that of latter 20th century dysmorphology and biochemical and molecular genetics: from its first description as a rare but characteristic multiple malformation syndrome known only to a handful of dysmorphologists, to a relatively common Garrodian defect with a complex molecular basis that has captured the attention of researchers and basic scientists from the fields as diverse as embryology, developmental biology, sterol biochemistry, epidemiology, and teratology. The discovery of the underlying biochemical defect - deficiency of 3beta-hydroxysteroid-Delta7-reductase (DHCR7), an enzyme catalyzing the last step of cholesterol biosynthesis, and the resultant generalized cholesterol deficiency - has led to an explosion of knowledge of this biochemical pathway and to a paradigm shift in the recognition of metabolic deficiencies as causes of dysmorphic syndromes. Characterization of the human DHCR7 gene and the identification of mutations in patients with SLOS have revealed a complex picture of molecular heterogeneity and provided insights into the structure and function of DHCR7. SLOS is the first metabolic malformation syndrome with profound effects on the body plan, and its discovery has paved the way to the discovery of a number of other defects of the cholesterol synthetic pathway.

Smith-Lemli-Opitz syndrome: the first malformation syndrome associated with defective cholesterol synthesis

Smith-Lemli-Opitz syndrome (SLOS), an autosomal recessive condition with multiple malformations, mental retardation, and growth failure, results from markedly reduced activity of the final enzyme in the cholesterol biosynthetic pathway, 7-dehydrocholesterol reductase (DHCR7). Clinical signs vary in severity, ranging from fetal loss to holoprosencephaly with multiple malformations to isolated syndactyly. The biochemical defect in SLOS is a deficiency of DHCR7, which results in an abnormally low cholesterol level, and increased amounts of intermediates of sterol biosynthesis. Animal models currently exist through the use of cholesterol biosynthesis inhibitors, from which a great deal has been learned. Pregnant rats treated with inhibitors of DHCR7 yield pups that have abnormal sterol profiles and craniofacial abnormalities characteristic of severe SLOS. Biochemical testing of human patients can be performed using gas chromatography/mass spectroscopy (GC/MS) to analyze the sterol content of tissues, amniotic fluid, or cell culture lysate. Numerous mutations have been identified in DHCR7 but seven individual mutations account for 67% of the total mutations reported in the literature. Clinical trials with SLOS are underway, with the goal of increasing the cholesterol concentration in the plasma and tissues through the administration of dietary cholesterol. Thus far, this approach has shown limited efficacy. Nevertheless, the recent identification of the biochemical and molecular genetic basis for SLOS is reason for optimism that the condition may one day yield to treatment.

The Smith-Lemli-Opitz syndrome

The Smith-Lemli-Opitz syndrome (SLOS) is one of the archetypical multiple congenital malformation syndromes. The recent discovery of the biochemical cause of SLOS and the subsequent redefinition of SLOS as an inborn error of cholesterol metabolism have led to important new treatment possibilities for affected patients. Moreover, the recent recognition of the important role of cholesterol in vertebrate embryogenesis, especially with regard to the hedgehog embryonic signalling pathway and its effects on the expression of homeobox genes, has provided an explanation for the abnormal morphogenesis in the syndrome. The well known role of cholesterol in the formation of steroid hormones has also provided a possible explanation for the abnormal behavioural characteristics of SLOS.

Blocking cholesterol synthesis impairs acquisition of the classically conditioned eyeblink response

Smith-Lemli-Opitz (SLO) syndrome is a congenital disorder characterized by severe mental retardation. Patients with SLO lack 7-dehydrocholesterol (7 dH) reductase, which catalyzes the last step of cholesterol synthesis. Administration of an agent that blocks 7 dH cholesterol reductase, BM 15.766 (BM), leads to a biochemical profile which resembles that of SLO patients, i.e., lower plasma, liver, and brain cholesterol levels accompanied by the appearance of the precursors 7 dH and 8 dH cholesterol. In this article we address the functional consequences of chronic BM treatment on new motor learning by assessing acquisition of the classically conditioned eyeblink response. Just-weaned rats were fed BM by gavage for four months, with half of these rats given exogenous cholesterol during the last two months of BM treatment. Acquisition of the eyeblink response was impaired in BM-treated rats. Impaired acquisition of the eyeblink response was not accompanied by alterations in responsiveness to either the conditioned or unconditioned stimulus. Exogenous cholesterol, a clinically relevant countertreatment, failed to correct for the learning impairment produced by BM treatment. Chronic treatment with a cholesterol synthesis-blocking agent impaired associative learning in just-weaned rats.

A simple PCR-based assay allows detection of a common mutation, IVS8-1G-->C, in DHCR7 in Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive multiple malformation disorder. A deficiency of the enzyme 7-dehydrocholesterol delta 7-reductase (DHCR7) is the primary abnormality in SLOS. The gene encoding DHCR7 has been cloned, and we have identified a mutation affecting the splice acceptor site 5' of exon 9 that occurs frequently in affected individuals. We developed a novel PCR-based assay to detect this common mutation in DHCR7. Using this assay, heterozygosity was detected for this mutation in 18 of 26 and homozygosity in 1 of 26 unrelated affected individuals. The high frequency of this mutation is suggestive of either a founder effect in our group of patients or a mutational hotspot. The simplicity and reliability of this assay will allow it to be used as a clinical test to aid in diagnosis of atypical cases, in carrier testing, in prediction of prognosis based on genotype, and in prenatal molecular genetic diagnostic testing.

Cholesterol and cataracts

Inherited defects in enzymes of cholesterol metabolism and use of drugs which inhibit lens cholesterol biosynthesis can be associated with cataracts in animals and man. The basis of this relationship apparently lies in the need of the lens to satisfy its sustained requirement for cholesterol by on-site synthesis, and impairing this synthesis can lead to alteration of lens membrane structure. Lens membrane contains the highest cholesterol content of any known membrane. The Smith-Lemli-Opitz syndrome, mevalonic aciduria, and cerebrotendinous xanthomatosis all involve mutations in enzymes of cholesterol metabolism, and affected patients can develop cataracts. Two established models of rodent cataracts are based on treatment with inhibitors of cholesterol biosynthesis. The long-term ocular safety of the very widely used vastatin class of hypocholesterolemic drugs is controversial. Some vastatins are potent inhibitors of cholesterol biosynthesis by animal lenses, can block cholesterol accumulation by these lenses and can produce cataracts in dogs. Whether these drugs inhibit cholesterol biosynthesis in human lenses at therapeutic doses is unknown. Results of clinical trials of 1-5 years duration in older patient populations indicate high ocular safety. However, considering the slow life-long growth of the lens and its continuing need for cholesterol, longterm safety of the vastatins should perhaps be viewed in units of 10 or 20 years, particularly with younger patients.

Non-cardiac malformations in individuals with outflow tract defects of the heart: the Baltimore-Washington Infant Study (1981-1989)

In the Baltimore-Washington Infant Study, a regional case-control study of 4,390 liveborn infants with cardiovascular malformations (CVM), 642 patients (14.2%) had outflow tract abnormalities, with extracardiac defects in 157 (approximately 25%) of them. Associated defects were found in 1/3 of patients with normal great arteries, but only in 1/10 of patients with transposition of great arteries (TGA). The extracardiac defects were especially rare in the groups "TGA with intact ventricular septum" and "TGA with ventricular septal defect". Patients with multiple associated defects outnumbered patients with isolated associated defects in the ratio 2.5:1. The associated defects were heterogeneous: 46 patients had chromosome abnormalities, 16 had different Mendelian syndromes, and 36 had associations (DiGeorge sequence and VACTERL association were the most frequent). A new syndrome of multiple congenital abnormalities including tetralogy of Fallot, and rare cases of chromosomal and Mendelian syndromes (distal trisomy 1q, tetrasomy 8p, Holzgreve syndrome) are described briefly. Sufficient variability of a spectrum of conotruncal defects in the patients with the same chromosomal or Mendelian syndromes suggests that at least in some cases different conotruncal defects are stages of the same morphologic spectrum. The analysis of conotruncal defects in sibs of patients with Mendelian syndromes may provide new data about the links between different definitive forms of CVM.

Prenatal diagnosis of Smith-Lemli-Opitz syndrome is possible by measurement of 7-dehydrocholesterol in amniotic fluid

Amniocentesis was performed at 17.3 weeks in a pregnancy with severe intrauterine growth retardation. Cytogenetic studies on amniocytes were normal, 46,XX, and the pregnancy was continued. The diagnosis of Smith-Lemli-Opitz syndrome was suspected in the neonatal period and confirmed by the presence of 7-dehydrocholesterol (7-DHC) in the plasma (0.4 mmol/l, normal = not detectable) associated with a low total cholesterol concentration (0.4 mmol/l, normal = 2.56 +/- 0.23). Retrospective analysis of the amniotic fluid sample revealed an elevated level of 7-DHC (0.022 mmol/l; normal = undetectable). Therefore measurement of 7-DHC levels in amniotic fluid during the second trimester of pregnancy is useful for the prenatal diagnosis of Smith-Lemli-Opitz syndrome in families at risk and should be considered in cases of severe growth retardation of unknown aetiology for which amniotic fluid is available and in which a normal chromosomal pattern in amniocytes is present.

Smith-Lemli-Opitz syndrome in a female with a de novo, balanced translocation involving 7q32: probable disruption of an SLOS gene

A 3-month-old infant girl had manifestations of the Smith-Lemli-Opitz syndrome (SLOS) including typical positional anomalies of the limbs, apparent Hirschsprung disease, cataracts, ptosis, anteverted nares, cleft of the posterior palate, small tongue, broad maxillary alveolar ridges, and abnormally low serum cholesterol levels. Chromosomal analysis showed a de novo balanced translocation interpreted as 46,XX,t(7;20)(q32.1;q13.2). We hypothesize that the translocation breakpoint in this case interrupts one SLOS allele and that the other allele at the same locus has a more subtle mutation that was inherited from the other parent. This case, as well as cytogenetic observations in other SLOS cases, suggests that SLOS could be due to autosomal recessive mutation at a gene in 7q32.

Lethal acrodysgenital dwarfism: a severe lethal condition resembling Smith-Lemli-Opitz syndrome

We report eight cases of a lethal association of failure to thrive, facial dysmorphism, ambiguous genitalia, syndactyly, postaxial polydactyly, and internal developmental anomalies (Hirschsprung's disease, cardiac and renal malformation). This syndrome is likely to be autosomal recessive and resembles Smith-Lemli-Opitz (SLO) syndrome. However, the lethality, the common occurrence of polydactyly, and the sexual ambiguity distinguishes this condition from SLO syndrome. A review of published reports supports the separate classification of this syndrome for which we propose the name lethal acrodysgenital dwarfism.

Female external genitalia and müllerian duct derivatives in a 46,XY infant with the smith-lemli-Opitz syndrome

We report on a 46,XY newborn infant with Smith-Lemli-Opitz (SLO) syndrome with female external genitalia, intraabdominal testes with epididymides and deferent ducts and a normally shaped uterus and vagina. Polydactyly, cleft palate, and several internal organ malformations were also present, and the patient died shortly after birth. Data on six reported male infants with SLO syndrome and female external genitalia suggest a correlation between degree of genital involvement and overall degree of severity. Scoring systems to quantify overall degree of severity (SLO score) and degree of genital involvement in males (genital score) were devised and applied to 122 reported cases from the literature. Statistical analyses showed a unimodal distribution of the SLO severity scores, and positive correlations between the SLO score and the genital score in males, the presence of polydactyly, and the presence of cleft palate. In 19 multiplex families the affected sibs were generally similar in their SLO scores. The above analyses suggest that the wide phenotypic variability in the SLO syndrome is determined by variable expressivity of the same entity as opposed to genetic heterogeneity. The observed phenotypic correlations naturally determine that males with complete feminization are among the more severe patients and tend to have polydactyly and cleft palate.

Genitourinary abnormalities associated with the Smith-Lemli-Opitz syndrome

The Smith-Lemli-Opitz syndrome is characterized by mental retardation, hypotonia, facial dysmorphism and abnormalities of the limbs, genitalia and kidneys. Since the latter 2 features have not been emphasized in the urological literature, the experience from the institution at which the syndrome was first described is reviewed and an illustrative case is reported. Upper urinary tract abnormalities were noted in 57 per cent and genital abnormalities in 71 per cent of the children evaluated.

A new syndrome with features of the Smith-Lemli-Opitz and Meckel-Gruber syndromes in a sibship with cerebellar defects

The Smith-Lemli-Opitz syndrome (SLOS) and the Meckel syndrome (MS) have been regarded as separate autosomal recessive entities. Recently, overlap of these two syndromes has been discussed. A sibship containing a probable new syndrome with features reminiscent of the SLOS and the MS is presented. The literature is reviewed with regard to the frequency of various malformations in these syndromes. Clinical manifestations and cerebellar abnormalities in these sibs are similar to those described in the Joubert syndrome (JS). These three cases may represent a new syndrome with features in common with SLOS, MS, and JS resulting from the same mutant gene, which exhibits considerable pleiotropy.

Smith-Lemli-Opitz syndrome-type II: multiple congenital anomalies with male pseudohermaphroditism and frequent early lethality

In 1964, Smith et al described a syndrome of microcephaly, growth and mental retardation, unusual facial appearance, syndactyly of toes 2 and 3, and genital abnormalities. Major structural malformations and early death have been uncommon in the many subsequent literature reports. We report on 19 infants with a phenotype we propose to call Smith-Lemli-Opitz syndrome (SLOS)-Type II, in which major structural abnormalities, male pseudohermaphroditism, and early lethality are common. Of these 19 patients, 18 had postaxial hexadactyly, 16 had congenital heart defect, 13 had cleft palate, and 10 had cataracts. Unusual findings seen in these patients at autopsy included Hirschsprung "disease" in five patients, unilobated lungs in six, large adrenals in four, and pancreatic islet cell hyperplasia in three. Comparison of our cases to 19 similar literature cases suggests the existence of a distinct phenotype that may be separate from SLOS as originally described. It is also inherited as an autosomal recessive, as documented by occurrence in one pair of sibs in this study and recurrence in three reported families.

Possible abnormalities of steroid secretion in children with Smith-Lemli-Opitz syndrome and their parents

In early infancy, two unrelated children with Smith-Lemli-Opitz syndrome were found to have elevated levels of androgen sulfates. When the steroid conjugates in the serum of normal infants were hydrolyzed and chromatographed on Sephadex LH-20, 4 androgen containing peaks (I, II, III, IV) were found. In the serum from these two infants with Smith-Lemli-Opitz syndrome, Peaks I and III were increased, but Peaks II and IV were absent. The parents of the two children, and of three additional unrelated children with Smith-Lemli-Opitz syndrome, had exaggerated 17-hydroxyprogesterone responses to an intravenous bolus of ACTH. These findings suggest that a defect in steroid metabolism may be linked to the Smith-Lemli-Opitz syndrome.

The Smith-Lemli-Opitz syndrome. A detailed pathological study as a clue to a etiological heterogeneity

An analysis of 33 autopsied cases with the Smith-Lemli-Opitz syndrome (including 8 cases from our practice) is presented. Polydactyly in dead SLOS children was found in 51% (17/33) of cases and occurred significantly more often in this group than in the whole group of SLOS (20-22%). Certain morphological differences in the type of renal, cerebral, pulmonary and pancreatic anomalies indicate the existence of two phenotypically similar SLOS: 1) with polydactyly; 2) without it. The presented data initiate SLOS heterogeneity.

Smith-Lemli-Opitz syndrome: neuropathological and ophthalmological observations

The case of a three-year-old boy with the Smith-Lemli-Opitz syndrome is reported. In addition to the constellation of skeletal and genital anomalies classically described in this syndrome, this patient had spontaneous opsoclonus-like eye movements, strabismus, lack of visual following responses and of opticokinetic reflexes. At autopsy the cerebellar vermis was found to be absent. There were retinal hemangiomas. Microscopical examinations showed loss of Purkinje cells and extensive neuronal degeneration within dentate nuclei, associated with patchy demyelination of cerebellar peduncles and central white matter. These findings may contribute to the explanation of the pathophysiology of opsoclonus and some of the neuro-ophthalmological findings.

A methodology for establishing a diagnostic index for syndromes of unknown etiology

A method has been developed to test for heterogeneity in syndromes of unknown etiology and to distinguish between patients with and without the syndrome. The validity of the method was tested on a group of patients suspected of having a syndrome that can be diagnosed by other means (Down syndrome), and was found to be effective. The method was then applied to a group of patients suspected of having a syndrome of unknown etiology (de Lange). It was shown that the group appears to be heterogeneous. A preliminary diagnosis of having or not having the syndrome was made in about 80% of the patients.

The pathological anatomy of the Smith-Lemli-Opitz syndrome

Two cases of the Smith-Lemli-Opitz syndrome are described, together with the autopsy findings. In both cases, the typical appearance and visceral malformations were present. Hypoplasia of the frontal lobes and corpus callosum, and aplasia of the splenium constitute abnormalities of the brain which may be useful in the diagnosis of this disorder at autopsy. The autosomal recessive mode of inheritance of this syndrome was confirmed.

Smith-Lemli-Opitz syndrome: review and report of two affected siblings

This paper reports two siblings with the Smith-Lemli-Opitz syndrome and reviews the literature on the subject. SLOS is a syndrome of multiple congenital anomalies with mental and growth retardation, unusual facies, genito-urinary and hand and foot abnormalities inherited as an autosomal recessive trait.