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Smith Lemli Opitz Syndrome


Smith Lemli Opitz syndrome is a congenital abnormality, characterized by mutations to the DHCR7 gene, which is located on chromosome 11. The mutation leads to a defective metabolic process as far as cholesterol is concerned, due to a deficiency in the 7-dehydrocholesterol reductase (DHCR7) enzyme


The clinical presentation of patients suffering from Smith Lemli Opitz syndrome tend to fluctuate between several phenotypes, depending on the extent of cholesterol deficiency. However, there typical findings associated with the syndrome, which include:

Additional characteristics may also accompany SLOS. Individual often exhibit epicanthic folds, ptosis, large ears, wrinkled skin on lower and upper eyelids, vision impairment (i.e cataracts) and gum abnormalities.

Epileptic phenomena may also manifest, alongside cardiovascular problems, hypotonia in children [10] and gastroenterological issues, such as obstruction of the bowel or pyloric stenosis.

Short Stature
  • Affected individuals have dysmorphism, short stature, failure to thrive, microcephaly, multiple congenital malformations, and mental retardation.[ncbi.nlm.nih.gov]
  • A syndrome with variable characteristics marked mainly by short stature, mental deficiency, microcephaly, postaxial polydactyly, cleft palate, cardiovascular defects, genital malformations, and other abnormalities associated with defective cholesterol[icd10data.com]
  • stature, and intellectual disabilities) 759.89 Rud's (mental deficiency, epilepsy, and infantilism) 759.89 Russell (-Silver) (congenital hemihypertrophy and short stature) 759.89 Seckel's 759.89 sick Silver's (congenital hemihypertrophy and short stature[icd9data.com]
  • stature, DD, cardiac defects, cryptorchidism) Support Groups [ edit ] Smith-Lemli-Opitz/RSH Foundation P.O.[en.wikibooks.org]
Weight Gain
  • In surviving infants, slow growth and poor weight gain is usual and feeding via a gastrostomy (a tube into the stomach) may be required. As the infant gets older, severe learning difficulties (see entry Learning Disability ) usually become evident.[contact.org.uk]
  • Consideration should be given to cholesterol supplementation to improve weight gain.[en.wikibooks.org]
  • After 6 months of age, the cholesterol-supplemented mice did demonstrate increased weight gain; however, this effect was also observed in control animals that fed on the cholesterol-supplemented chow.[doi.org]
  • Because children with SLOS have low muscle mass, careful monitoring of weight gain and growth is necessary so that overconsumption of calories does not lead to obesity.[ncbi.nlm.nih.gov]
  • Failure to thrive and poor weight gain despite adequate caloric intake are common features of Smith-Lemli-Opitz syndrome, which were seen in C.[doi.org]
Syndactyly of Second and Third Toes
  • C. showing ambiguous genitalia and D. showing syndactyly of second and third toes.[indianpediatrics.net]
  • The limbs had syndactyly of second and third toes with short and stubby fingers (Figure 4) and simian crease. Genital examination showed pen scrotal hypospadias with undescended testis (Figure 5). Systemic examination showed pan systolicmurmur.[omicsgroup.org]
Dysmorphic Face
  • We present the case of an infant born by cesarean section for fetal suffering (Apgar score 8/1′–8/5′), with multiple malformations (dysmorphic face, polydactyly, syndactyly, hypospadias, cryptorchidism) detected already at birth.[endocrine-abstracts.org]
  • SLOS is characterized by a plethora of abnormalities involving mainly the brain and the genitalia but also the cardiac, skeletal and gastroenteric system, typical dysmorphic facial features, and variable degrees of developmental delay and intellectual[ncbi.nlm.nih.gov]
Failure to Thrive
  • Affected individuals have dysmorphism, short stature, failure to thrive, microcephaly, multiple congenital malformations, and mental retardation.[ncbi.nlm.nih.gov]
  • We found correlations between multiple congenital malformations, failure to thrive and low plasmatic cholesterol measurement.[ncbi.nlm.nih.gov]
  • Abstract The Smith-Lemli-Opitz (SLO or RSH) syndrome is an autosomal recessive disorder characterized by a recognizable pattern of minor facial anomalies, congenital anomalies of many organs, failure to thrive, and mental retardation.[ncbi.nlm.nih.gov]
  • Thirteen of the 26 children experienced failure to thrive, and 10 children required gastrostomy.[ncbi.nlm.nih.gov]
  • He had a normal perinatal period; however, his early infancy was complicated by poor feeding, episodes of loose stools, failure to thrive, and several episodes of unexplained drowsiness.[ncbi.nlm.nih.gov]
Systolic Murmur
  • On examination, he had cyanosis, facial dysmorphism, obesity, bilateral cryptorchidism, hypospadias, inverted nipples, and systolic murmur over the left parasternal area. Investigations revealed a decreased serum cholesterol and elevated 7DHC.[ncbi.nlm.nih.gov]
  • Our patient has suffered from sunlight intolerance since early infancy, with redness and pruritus of sun-exposed skin developing within minutes of sun exposure.[ncbi.nlm.nih.gov]
Skeletal Dysplasia
  • dysplasia MVRCS association Nail-patella syndrome Nance-Horan syndrome Neu-Laxova syndrome Neurocutaneous syndrome Nodular embryo Noonan syndrome Noonan's syndrome Oculo-cerebro-cutaneous syndrome Oculodentodigital syndrome Oculodento-osseous dysplasia[icd9data.com]
  • Dysplasia, and Abducens Palsy Mental Retardation, X-Linked Merlob Grunebaum Reisner Syndrome MERRF Syndrome MERRF/MELAS Overlap Syndrome Mesomelia-Synostoses Syndrome Metabolic Syndrome Metaphyseal Dysostosis, Mental Retardation, and Conductive Deafness[rgd.mcw.edu]
  • Clinical Characteristics Ocular Features: A large number of ocular anomalies have been found in SLO syndrome but the most common is blepharoptosis of some degree. No consistent pattern of ocular abnormalities has been reported.[disorders.eyes.arizona.edu]
  • Blepharoptosis in children: our experience at the light of literature. Clin Ter 2010;161:241–3. [24]. Jubbal KT, Kania K, Braun TL, et al. Pediatric blepharoptosis. Semin Plast Surg 2017;31:58–64. [25]. Gutowski NJ, Chilton JK.[journals.lww.com]
  • Cases reported between mid 1960’s and late1970’s suggested that both male and female were affected with a autosomal recessive inheritance pattern, and additional features were blepharoptosis, genital hypoplasia, micrognathia, polydactyly, cleft palate[path.upmc.edu]
Head Banging
  • Behavioral signs/symptoms include sensory hyperreactivity, irritability, sleep cycle disturbance, self-injurious behavior (hand biting and/or head banging), autism spectrum behaviors (46%-53%), temperament dysregulation, and social and communication deficits[ncbi.nlm.nih.gov]
Narrow Forehead
  • At 31 weeks of gestation, the following fetal malformations were detected on an ultrasound: atrioventricular septal defect (AVSD), aortic coarctation, shortening of the lower limbs, narrow forehead, hyperthelorism, micrognathia, anteverted nares, ambiguous[ncbi.nlm.nih.gov]
  • A characteristic craniofacial pattern profile was universally present: narrow forehead, brachycephaly, short palpebral fissures, short nasal ridge, anteverted nares, flat face, normal jaw width, and retrognathia.[ncbi.nlm.nih.gov]
  • The following are the most commonly observed features: Characteristic facial features (narrow forehead, epicanthal folds, ptosis, short mandible with preservation of jaw width, short nose, anteverted nares, and low-set ears) 2-3 syndactyly of the toes[ncbi.nlm.nih.gov]
Beaked Nose
  • The craniofacial dysmorphism in patients diagnosed with this condition consists of microcephaly, a low anterior hair line, downslanting palpebral fissures, ocular signs (including ptosis, epicanthus, and strabismus), a broad nasal bridge, a beaked nose[journals.lww.com]
  • The patient had a persistent urogenital sinus, posterior labial fusion without clitoromegaly. She presented with a salt-wasting syndrome on day 4. Adrenal insufficiency was confirmed.[ncbi.nlm.nih.gov]
  • Other findings include persistent urogenital sinus and posterior labial fusion without clitoromegaly in a female with an XX karyotype [ Chemaitilly et al 2003 ] and precocious puberty in girls with SLOS [ Starck et al 1999 ; Irons, unpublished].[ncbi.nlm.nih.gov]


Smith Lemli Opitz syndrome can be diagnosed both antenatally and postnatally.


The first screening step is an ultrasonographic evaluation of the embryo. If features that suggest a potential SLOS are observed, 7DHC levels can be calculated through chorionic villus sampling or amniocentesis. Genetic testing can only be performed if a member of the family is affected by SLOS and, therefore, an identification of the responsible mutation is already known.

Generally, if a mother exhibits a decreased concentration of unconjugated estriol, it is considered an indication of trisomy; if, however, genetic testing reveals a normal karyotype, the finding is increasingly indicative of SLOS. Maternal urine of women pregnant with a child affected by SLOS has been found to contain equine estriols and this test is likely to render the diagnosis of the syndrome in a non-invasive way possible [11].


A clinical examination usually reveals findings compatible with SLOS. Further testing, including blood tests and imaging studies, is required to establish a definitive diagnosis of the condition.

An affected newborn is expected to exhibit low LDL levels and total cholesterol concentration, as well as elevated blood levels of 7DHC.

Additionally, a child has to be evaluated with a computerized tomography (CT) or magnetic resonance imaging (MRI) scan, in order to illustrate brain abnormalities, as well as a US scan for kidney deformities. The possibility of pyloric stenosis and Hirschsprung disease has to be assessed as well, with the aid of an abdominal US scan, a barium swallow and abdominal x-ray or barium enema respectively.

  • These patients presented with hyponatremia, hyperkalemia, and decreased aldosterone-to-renin ratio, which is a sensitive measure of the renin-aldosterone axis.[ncbi.nlm.nih.gov]
  • Adrenal insufficiency with hyponatremia has been reported in 3 patients with severe SLOS; in those cases it was thought to be caused by aldosterone deficiency because it responded to mineralocorticoid replacement.[ncbi.nlm.nih.gov]
  • They all had electrolyte abnormalities (hyperkalemia, hyponatremia, hypocalcemia), necrotizing enterocolitis, sepsis-like episodes and midline defects including the branchial and cardiac defects.[ncbi.nlm.nih.gov]
  • His blood glucose and serum bicarbonate levels were low and serum electrolytes revealed hyponatremia with hyperkalemia. Serum spot cortisol level was low normal and 17-hydroxyprogesterone level was low.[ncbi.nlm.nih.gov]
Testosterone Decreased
  • On the other hand, the patient had a positive biological response to exogenous testosterone (decrease in sex hormone-binding globulin serum levels). She was orchidectomized at the age of 33 mo.[ncbi.nlm.nih.gov]


As of yet, there is no cure for Smith Lemli Opitz syndrome [12] and there has been no definitive suggestion either, as to the exact type of supportive treatment that will be needed.

A universally accepted fact is the necessity to treat symptoms and defects emerging from the syndrome itself. Conjoined fingers or toes and congenital cardiac defects have to be surgically treated early in the course of the disease, a pylorotomy can be performed in order to treat the stenosis and cleft palate can also be surgically corrected. Individuals may also benefit from surgical treatment if Hirschsprung disease is detected or if polydactyly is present. Hormonal supplements are administered to compensate for their low levels in the plasma and devices used to improve hearing ability will be useful to the patients suffering from hearing loss or various degrees.

With regard to the cholesterol deficiency itself, inhibitors of hydroxymethylglutaryl-coenzyme-A-reductase and cholesterol supplements have been attempted as a therapeutic procedure, but it has yet to be determined what dose should be given, which form of cholesterol supplements and whether there is a need for bile acid supplementation as well. The most important question that needs further research in order to be answered, is whether cholesterol supplement will actually benefit the patients in any way. Cholic acid supplementation has received FDA approval for the treatment of SLOS. Researchers have attempted to boost cholesterol concentration both with pharmacologically administered cholesterol compounds and cholesterol-rich food products, such as whipping cream and egg yolks.

In order to improve the chances of fetal development, IV and intraperitoneal transfusion of fresh-frozen plasma to the embryo has been attempted during pregnancy. The results were positive and it seemed that cholesterol was admitted into the red blood cells of the fetus.

Statins, which are used in healthy individuals to lower cholesterol levels in the blood, were found to not have this effect on patients with SLOS. They have been administered with the belief that they would lower 7DHC levels in the plasma, but the respective study revealed no actual benefits to the patients [13].


There is very little data on the long-term prognosis of patients suffering from SLOS. It is widely accepted that individuals who display a blood cholesterol level of <20 mg/dL have a poor prognosis and usually do not reach adulthood.

There is one well-documented case concerning one of the three patients originally described by Smith, Lemli and Opitz. The patient was monitored by another medical team in order to evaluate the progress of the disease for 30 years.

The male patient [9], who had reached adulthood, exhibited significant mental disability, epileptic phenomena and aggressive behavior; for the latter two he received drug treatment. His state of general health was very good, although typical outer appearance characteristics remained evident. He was put on an appropriate diet which increased cholesterol intake and the patient exhibited a significant improvement in terms of mood, aggressiveness and communicative skills after two months. Blood tests carried out at intervals revealed that the patient failed to maintain adequate cholesterol levels without supplementation.


SLOS is inherited with an autosomal recessive pattern [3]. Regarding the genetic mutations, 4-5 distinct mutations have been identified so far, which suggests that in cases of consanguinity, the risk of the parents carrying the same defective gene is significantly higher and therefore, careful genetic counseling must be provided before the decision to have children is made. As a general rule, carriers of the mutated genes exhibit no symptoms.


There is little consent on the matter of SLOS incidence in different parts of the world. The first calculation by Lowry and Yong showed that SLOS occurred once (1) every 40,000 births in British Columbia [4], but the rate augmented to 1 per 20,000 births when the study evaluated patients with indications towards the syndrome but no definitive diagnosis. Another research conducted in the Czech Republic calculated the incidence of SLOS as amounting to 1 per 10,000 births, a rate which is significantly higher than the two previous estimations [5].

More recent studies have shown that the SLOS incidence is considerably lower than the aforementioned numbers, namely from 1/60,000 to 1/90,000 in the USA and United kingdom respectively. It has become clear, through various studies that ethnicity plays an important role in the incidence of SLOS.

Sex distribution
Age distribution


The syndrome was first described by Smith, Lemli and Opitz in 1964 [6]. Its causes where unknown at the time and it was not until 1993 [7] that it was proven that patients exhibited low levels of cholesterol in the blood and increased levels of a substance that precedes cholesterol in the maturation process, 7DHC. The gene that encodes for 7DHC (DHCR7) was found to be responsible for producing a molecular substance that cannot adequately evolve into cholesterol, rendering SLOS an inherited metabolic defect.

The functionality of cholesterol as a constructing substance was also later discovered and this discovery shed light on why the affected patients displayed the respective symptomatology. Cholesterol is now known to act as a substrate from which hormones and bile are made, as a component of cellular membranes and a myelin component. Cholesterol also acts as a trigger for the sonic hedgehog protein found in the fetus, which is involved in the construction of many fetal systems. Failure to activate the sonic hedgehog protein alongside multiple other defects in its activation and pathway are thought to be responsible for the symptoms displayed by individuals who are born with SLOS.

Patients with SLOS have also been found to have increased isoprenoids [8], whose role, however, has not yet been fully understood.


There is no way to prevent SLOS, since it is an inherited condition. Genetic counseling in families with members affected by it may lower the chances of giving birth to offspring with the syndrome.


Smith Lemli Opitz syndrome (SLOS) is an inherited condition characterized by the absence or diminished production of cholesterol, due to a lack of 7-dehydrocholesterol reductase [1]. Given that cholesterol is indispensable to the organism, as it mediates cellular structure, hormonal production and the production of digestion-related acidic compounds, its complete lack or decreased levels can affect the body's development in a variety of ways.

Children may be born with a complete inability to produce cholesterol or with very little available cholesterol; these patients exhibit a severe clinical picture. They are born with diminished muscular tone, cleft palate and a small-sized head. Dietary habits are compensated, as most display smaller-than-normal sized stomachs that lead to emesis or a defective sucking reflex. Polydactyly may be observed or fingers and toes that are conjoined. Deformities of the genitalia may also be present [2] and the individuals have varying degrees of mental retardation.

Individuals who have a moderate lack of cholesterol exhibit a milder clinical picture, characterized by hindered growth, conjoined fingers or toes and a mild mental retardation, whereas people with insignificant lack of cholesterol may also have clinically insignificant symptoms.

Patient Information

Smith Lemli Opitz syndrome, abbreviated as SLOS, is a congenital anomaly. Patients who have this syndrome are borne with a defective gene, which is responsible for producing a compound, 7DHC, which matures into cholesterol. The syndrome causes an abnormal type of 7DHC which cannot be transformed into cholesterol and, as a result, patients have increased 7DHC in their blood and low cholesterol.

Cholesterol is known to be a part of the cells; without it, cellular structures are incomplete and this caused innumerable problems in their function. Hormones are also produced with cholesterol and patients with this syndrome cannot produce the amount of functional hormones needed by the organism. Cholesterol also partakes in the formation of brain structures.

A person is always born with SLOS and they cannot acquire it at a later stage; however, sometimes the disease becomes evident later on in life. Symptoms depend on how much cholesterol a patient is missing and vary from insignificant to severe. Generally, typical symptomatology includes the following:

SLOS can be diagnosed before a baby is born. A doctor will usually observe something abnormal on a US scan and will perform amniocentesis or other tests in order to diagnose it. Once an individual is born, the syndrome can be diagnosed by measuring cholesterol levels and the 7DHC compound in the blood.

There is no treatment for SLOS syndrome. Lots of supportive therapies have been suggested but there is no particular consent as to what should be done exactly. Further problems, like heart problems, gastrointestinal defects and finger structural abnormalities can be surgically corrected. A person may receive supplements of hormones or cholesterol or be encouraged to consume larger quantities of foods rich in cholesterol.



  1. Correa-Cerro, Lina S, Porter, et al. 3β-Hydroxysterol Δ7-reductase and the Smith–Lemli–Opitz syndrome. Molecular Genetics and Metabolism. 2005; 84 (2): 112–26.
  2. Joseph DB, Uehling DT, Gilbert E, et al. Genitourinary abnormalities associated with the Smith-Lemli-Opitz syndrome. J Urol. 1987; 137: 719-721.
  3. Waterham HR, Hennekam RC. Mutational spectrum of Smith-Lemli-Opitz syndrome. Am J Med Genet C Semin Med Genet. 2012 Nov 15; 160C(4):263-84.
  4. Lowry RB, Yong SL. Borderline normal intelligence in the Smith-Lemli-Opitz (RSH) syndrome. Am J Med Genet. 1980; 5:137–143.
  5. Kelley RI. A new face for an old syndrome. Am J Med Genet. 1997; 68:251–256.
  6. Smith DW, Lemli L, Opitz JM. A newly recognized syndrome of multiple congenital anomalies. J Pediatr. 1964 Feb; 64:210-7.
  7. Irons M, Elias ER, Tint GS. Abnormal cholesterol metabolism in the Smith-Lemli-Opitz syndrome: report of clinical and biochemical findings in four patients and treatment in one patient. Am J Med Genet. 1994 May 1; 50(4):347-52.
  8. Pappu AS, Connor WE, Merkens LS, et al. Increased nonsterol isoprenoids, dolichol and ubiquinone, in the Smith-Lemli-Opitz syndrome: effects of dietary cholesterol. J Lipid Res. 2006 De;. 47(12):2789-98.
  9. Pauli RM, Williams MS, Josephson KD. Smith-Lemli-Opitz syndrome: thirty-year follow-up of "S" of "RSH" syndrome. Am J Med Genet. 1997 Jan 31; 68(3):260-2.
  10. Wassif CA, Zhu P, Kratz L, et al. Biochemical, phenotypic and neurophysiological characterization of a genetic mouse model of RSH/Smith-Lemli-Opitz syndrome. Hum Molec Genet. 2001; 10: 555-564.
  11. Shackleton CH, Roitman E, Kratz LE. Equine type estrogens produced by a pregnant woman carrying a Smith- Lemli-Opitz syndrome fetus. J Clin Endocrinol Metab. 1999 Mar; 84(3):1157-9.
  12. Svoboda MD, Christie JM, Eroglu Y, et al. Treatment of Smith-Lemli-Opitz syndrome and other sterol disorders. Am J Med Genet C Semin Med Genet. 2012 Nov 15; 160C(4):285-94.
  13. Haas D, Garbade SF, Vohwinkel C, et al. Effects of cholesterol and simvastatin treatment in patients with Smith-Lemli-Opitz syndrome (SLOS). J Inherit Metab Dis. 2007 Jun; 30(3):375-87.

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Last updated: 2019-07-11 20:27