Steiner Lab Current Projects
The Steiner Lab studies rare genetic disorders in which the body cannot properly synthesize or process cholesterol or other non-sterol isoprenoids. These disorders are caused by defects in the enzymes involved in the biochemical pathways that synthesize, absorb, or transport cholesterol or isoprenoids or convert cholesterol into bile acids. These disorders include Smith-Lemli-Optiz syndrome (SLOS), cerebrotendinous xanthomatosis (CTX), mevalonate kinase deficiency, Sjögren Larsson syndrome (SLS), Niemann-Pick Type C and sitosterolemia. The lab also studies phenylketonuria (PKU), autism, osteogenesis imperfecta and lysosomal storage diseases.
The most common human disorder of cholesterol synthesis is Smith-Lemli-Opitz syndrome (SLOS). SLOS is due to a mutation in the 7-dehydrocholesterol ∆7reductase gene (DHCR7) encoding the final enzyme in the cholesterol synthesis pathway. This disorder is associated with intellectual disability and birth defects. SLOS is characterized by usually low cholesterol levels and elevated levels of cholesterol precursors, in particular 7-dehydrocholesterol (7-DHC). The current research in SLOS is to correlate biochemical and clinical characteristics, and whole body cholesterol accretion with cholesterol dietary intake, cholesterol absorption and cholesterol synthesis. Children receiving dietary cholesterol supplementation and those receiving dietary supplementation with simvastatin will be evaluated.
Smith-Lemli-Opitz Syndrome (SLOS)
What Is Smith-Lemli-Opitz Syndrome?
Smith-Lemli-Opitz Syndrome (SLOS) is a genetic disorder of cholesterol metabolism, in which insufficient cholesterol is produced by the body. Cholesterol is an essential component of cell membranes and myelin, as well as being important in embryonic development. Cholesterol is synthesized in the body through a complex set of enzymatic chemical reactions. In unaffected individuals, cholesterol is both ingested through the diet and produced endogenously.
However, in individuals with SLOS one of these enzymes, 7-dehydrocholesterol Δ 7 reductase (DHCR7), is defective. This causes decreased synthesis of cholesterol. At the same time, the defective enzyme is unable to process the cholesterol precursor 7-dehydrocholesterol (7-DHC), into cholesterol. This results the in accumulation of 7-DHC in the blood and tissues of the body.
Symptoms of Smith-Lemli-Opitz Syndrome
The signs and symptoms and severity of SLOS varies greatly between individuals. Most individuals with SLOS have birth defects and intellectual disability. These signs and symptoms vary widely between individuals. Although the majority of those with SLOS have significant signs and symptoms of the condition, there are some very mildly affected individuals who show almost no features of the disorder.
Common signs and symptoms include:
- syndactyly (webbing) of toes
- heart defects
- underdeveloped external genetalia
- microcephaly (small head)
- hearing impairment
- ophthalmologic abnormalities
- sucking, swallowing, and feeding problems
- slow growth or failure to thrive
- intellectual disability/learning
- cleft palate
- distinctive facial features
Genetics and Biochemistry of SLOS
Smith-Lemli-Opitz syndrome is an autosomal recessive Mendelian disorder. Both parents of a child with SLOS are carriers of one abnormal DHCR7 gene, but show no physical evidence of the disorder. There is a 1 in 4 chance that a child born to parents who are both carriers of SLOS will have the disorder. The incidence of SLOS is generally estimated at between 1/15,000 and 1/60,000 although more current research shows that carrier frequency is 1 in 30, and some cases may be missed, so that the incidence may be higher than that observed.
In unaffected individuals, blood cholesterol concentrations are above 100mg/dL and concentrations of 7-DHC are near 0. At diagnosis, children with SLOS typically have cholesterol concentrations less than 50mg/dL and high levels of the cholesterol precursor 7-DHC (usually between 5mg/dL and 20mg/dL), as well as high concentrations of 8-DHC (an isomer of 7-DHC). However, cholesterol concentrations can be normal, so screening by measurement of cholesterol alone is to be avoided.
Cholesterol is an essential building block of all cell membranes, is the precursor to steroid hormones and bile acids, and is high concentrations in the myelin sheaths surrounding neurons in the brain. Typically, SLOS patients lack the ability to synthesize enough cholesterol for normal growth and development leading to the wide variety of clinical symptoms manifested in these patients.
In addition to being a major cell component, cholesterol is also important during embryonic development. Shh, an important protein in limb patterning and craniofacial development relies on cholesterol for proper autoprocessing during embryonic development. The decreased cleaveage of Shh precursor proteins due to deficiency of cholesterol may result in the dysmorphogenesis noted in many SLOS patients, though newer research suggests that Shh signalling is affected by DHCR7.
Finally, studies in rats have shown that 7-DHC likely plays a role in the pathogenesis of SLOS as well. 7-DHC has been shown to impair learning, to inhibit embryonic growth, and to enhance toxic effects, probably through oxidized by-products.
Dr. Steiner is also principal investigator of a new multicenter grant to investigate several related disorders: Sterol and Isoprenoid Research Consortium, (STAIR), as a Rare Disease Clinical Research Consortium (RDCRC), for the Rare Disease Clinical Research Network (RDCRN)
STAIR institutions include:
- Oregon Health & Science University (OHSU) (Robert Steiner/Jean-Baptiste Roullet)
- Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) (Forbes D. Porter)
- Children’s Hospital of Pittsburgh of University of Pittsburgh Medical Center (Jerry Vockley)
- Cincinnati Children’s Hospital Medical Center (CCHMC)/University of Cincinnati Medical Center (UCMC) (James Heubi/Laura Woollett)
- Michigan Tech University (K.Michael Gibson)http://www.bio.mtu.edu/faculty/gibson.htm
- University of Nebraska Medical Center (UNMC) (William Rizzo).
- In addition, Peter Jones, University of Manitoba, will participate as Core Lab Director. www.rcffn.ca
OHSU is the administrative home of STAIR. The RDCRN was created to facilitate collaboration among experts in many different types of rare diseases. Our goal is to contribute to the research and treatment of rare diseases by working together to identify biomarkers for disease risk, disease severity and activity, and clinical outcome, while also encouraging development of new approaches to diagnosis, prevention, and treatment” (http://rarediseasesnetwork.epi.usf.edu/stair/index.htm). The disorders studied by the consortium are SLOS, MKD and HIDS, SLS, CTX, Niemann Pick Type C and sitosterolemia.
Mevalonate Kinase Deficiency (MKD)
What Is Mevalonate Kinase Deficiency?
Mevalonate Kinase Deficiency (MKD) is an inborn error of the biosynthesis of cholesterol and isoprenoids. An accumulation of mevalonic acid (detected in urine) results from the deficiency of mevalonate kinase (ATP mevalonate 5-phosphotransferase; EC 220.127.116.11). Â The deficiency causes two distinct clinical syndromes: mevalonic aciduria (MVA, MIM 251170) and hyperimmunoglobulinemia D with periodic fever syndrome (HIDS, MIM 260920).
Common signs and symptoms include:
- developmental delay
- various dysmorphic features
- psychomotor retardation
Genetics and Biochemistry of MKD
MKD (and HIDS) is an autosomal recessive disorder of the gene, MK, located on chromosome 12q24. Mutations cause a deficiency of mevalonate kinase (ATP mevalonate 5-phosphotransferase. Most of the mutations that have been tested seem to affect the folding or stability of the enzyme rather than the catalytic activity
There is no established treapeutic treatment. In some cases, dietary supplementation of cholesterol has been tried. Corticosteroids are beneficial during the clinical crises. Additional long-term administration of ubiquinone-50, together with vitamin C and E appeared to further stabilize the clinical course.
Cerebrotendinous Xanthomatosis (CTX)
What Is Cerebrotendinous Xanthomatosis?
Cerebrotendinous Xanthomatosis (CTX) is a genetic lipid-storage disorder, in which cholestanol, a product of cholesterol metabolism, accumulates in the body. CTX is caused by a mutation in the CYP27A1 gene.
Cholestanol and other pathway intermediates accumulate in the blood and both and cholesterol and cholestanol accumulate in the, brain, and other tissues. In addition patients with CTX also have a deficiency in bile acid production.
Symptoms of CTX
The symptoms of CTX can vary widely between patients. In some patients the first sign of the disorder is severe childhood diarrhea and cataracts. As the patient ages, more neurological features may become present. Patients lose mental capability and begin to show signs of ataxia. Untreated patients usually become bed ridden as they age. Common signs and symptoms of CTX include:
- tendon xanthoma
- progressive ataxia
- cholesterol deposits in the cerebellum
- intellectual disability
- chronic diahrrea
- cerebral or cerebellar atrophy
- prolonged neonatal cholestatic jaundice
- other psychiatric symptoms
- EEG abnormalities
- premature arteriosclerosis
- epileptic seizures
Genetics and Biochemistry of CTX
Cerebrotendinous Xanthomatosis is an autosomal recessive disorder. The incidence of CTX is generally estimated at 1/50,000. CTX patients have a defect in bile acids synthesis. The disease is caused by mutations in the sterol 27-hydroxylase gene (CYP27A1), a mitochondrial cytochrome P-450, which hydroxylates a variety of sterols at the C27 position in association with two protein cofactors, adrenodoxin and adrenodoxin reductase. Sterol 27-hydroxylase catalyzes the first step in the oxidation of the side chain of sterol intermediates in the bile acid synthesis pathway. Cholestanol, the 5-alpha-dyhydro derivative of cholesterol, is enriched relative to cholesterol in all tissues.
In unaffected individuals, blood cholestanol concentrations are below 0.48±0.03 mg/dL. In patients with CTX, plasma cholestanol concentrations can be more than 10 times higher than that of normals. At diagnosis, patients with CTX typically have cholestanol concentrations greater than 3mg/dL and cholesterol concentrations are often normal or low-normal.
In addition to abnormal concentrations of cholestanol, patients with CTX also excrete very high concentrations of bile alcohols in the urine and subnormal concentrations of bile acids in the stool. CYP27A1 is responsible for the production of the bile acid, chenodeoxycholic acid (CDCA). In patients with CTX, CDCA is virtually absent in bile.
CTX can be effectively treated with supplementation of CDCA. Replacement of CDCA inhibits the conversion of cholesterol to cholestanol and reduces the production of bile alcohols. After treatment with CDCA, concentrations of cholestanol nearly normalize in most patients. In addition, gastrointestinal, EEG, and neurological symptoms remain stable and in some cases improve.
Additional resources for SLS:
- at UNMC
- A summary of SLS from eMedicine
- The United Leukodystrophy Foundation-SLS
- Rizzo, WB. Sjogren-Larsson syndrome: Molecular genetics and biochemical pathogenesis of fatty aldehyde dehydrogenase deficiency Mol Genet Metab. 2007 Jan.
Phenylketonuria (PKU) is an inborn error of metabolism caused by a deficiency of phenylalanine hydroxylase (PAH). PKU is characterized by an inability of the body to utilize the essential amino acid, phenylalanine. PAH normally converts phenylalanine to tyrosine. In PKU, the lack of functional PAH results in the buildup of phenylalanine, and its' derivatives, in the blood, brain, and body tissues. A normal blood phenylalanine level is about 1 mg/dl. In classic PKU, levels may range from 6 to 80mg/dL, but are usually greater than 30mg/dL. The two major consequences of PKU are: (1) toxic levels of phenylalanine in the body and (2) high ratio of phenylalanine to tyrosine associated with impairment of the production of neurotransmitters.
Classic PKU affects about one of in every 10,000 to 20,000 Caucasian or Oriental births. The incidence of PKU in other ethnic groups is far less. PKU is an autosomally inherited recessive diorder and thus affects males and females equally.
The symptoms of untreated PKU include:
- Skin rashes (eczema)
- Jerking movements of the arms or legs (spasticity)
- Unusual positioning of hands
- Delayed mental and social skills
- Mental retardation
- A distinctive "mousy" odor to the urine, breath, and sweat
- Light complexion, hair, and eyes
Without treatment, most infants with PKU develop mental retardation. The symptoms of PKU and other birth defects can be present in babies born as carriers to PKU mothers whose Phenylalanine concentrations are poorly controlled.
Genetics and Biochemistry of PKU
Phenylketonuria (PKU) is an autosomal recessive disorder. The gene, PAH, maps to chromosome 12q24.1. The defective enzyme, PAH, normally converts phenylalanine to tyrosine. In PKU, the lack of functional PAH results in the buildup of phenylalanine, and its' derivatives, in the blood, brain, and body tissues
PKU treatment is based on a phenylalanine-limited diet that includes restricton of most foods of animal origin. This diet is begun during the first days or weeks of life and often lasts for life. A carefully maintained diet can prevent intellectual disability as well as neurological, behavioral and dermatological problems. It is generally believed that keeping blood phenylalanine concentrations in the range of 2-6mg/dL is the safest, especially in infancy and early childhood. Frequent blood monitoring should be done to achieve this goal.
The restricted diet required for PKU patients is very low in protein. Fruits, vegetables, and specially made low-protein pasta and rice are supplemented with a nutritional formula. The formula is begun in infancy and continued through adulthood. The formula is high in protein but very low in phenylalanine and provides additional calories and vitamins to PKU patients.
If the restricted diet is followed, nearly all PKU patients will live fairly normal lives with little cognitive impairment.
Despite treatment there can be subtle neuropsychological differences. Phenylalanine has been shown to decrease activity of HMGCoA reductase (HMGCR), the primary enzyme controlling cholesterol synthesis. Brain of individuals with PKU, even those with well-treated PKU, may show hypomyelination. The typical low cholesterol diet would result in a higher whole body cholesterol synthesis in PKU compared to controls. In most of the body, HMGCR inhibition by phenylalanine would be overridden by the low cholesterol diet, but the brain would bear the full effect of HMGCR inhibition, since dietary cholesterol does not cross the blood brain barrier and therefore does not reach the brain.
Autism is a behaviorally defined neurodevelopmental disorder usually diagnosed in early childhood that is characterized by impairment in reciprocal communication and speech, repetitive behaviors, and social withdrawal.
Autism presently affects 1 in 150-200 individuals in the world. Autism affects more males than females and is estimated to have greater than 90% heritability. Patients usually begin to exhibit abnormal behavior as infants. An autistic child may be indifferent to his or her caregiver and become overly agitated or overly passive when interacting with other people. As autistic children get older, they may fall behind their peers in areas of communication, social skills, and cognition.
In addition to these abnormal social interactions, dysfunctional behaviors may start to appear. Behaviors such as rocking and hand-flapping, self-injury, sleeping or eating problems, poor eye contact, and insensitivity to pain become more common. Autistic individuals may also have physical impairments that can involve auditory, visual, tactile, and taste. Autistic children are often insistent on "same-ness" and are easily upset by even small changes to a routine.
Autism and SLOS
Although both genetic and environmental factors are thought to be involved in causing autism, none have been reproducibly identified. There are several genetic disorders that present with symptoms similar to those of autism. In these cases, the underlying genetic disease is what causes autistic behavior in these patients. Landau-Kleffner Syndrome and Rett syndrome are two examples. Recently, SLOS has been targeted as genetic disorder that may present as an Autism Spectrum Disorder (ASD) in some patients.
Evidence suggests that some children with autism may have SLOS. SLOS patients often exhibit many of the characteristic behaviors of autism. The most common include self-injury, under-developed communication skills, poor eye contact, staring into open areas without focus, attachment to routine, and hyper-sensitivity. The inability to eat foods that are highly flavorful or strangely textured is a difficulty common to both SLOS and autism.
In our studies we have found near universal presence of autism spectrum disorders in children with SLOS (Sikora et al 2006 Amer J Med Genet A140:1511). In another study, fourteen patients with SLOS were evaluated for autistic spectrum disorders. Approximately 3/4 of the children evaluated had an ASD. Tierney and colleagues (Amer J Med Genet 2001.98:191) found that, out of a group of 56 SLOS patients, 50% met the diagnostic criteria for an ASD.
Neither 7- nor 8-DHC levels correlated with ASD severity in either of these studies. However, data collected at the Kennedy Krieger Institute has shown that approximately 20% of the children with autism sampled had cholesterol levels below the 5th percentile for children their age.
A mouse model for SLOS has been developed in which the Dhcr7-/- mouse has hypermorphic development of serotonin (5-HT) neurons. Current evidence has shown that serotonin plays a significant role in autism spectrum disorders. Drugs selectively acting on the serotonin system are some of the most effective treatments for maladaptive behaviors seen in autism. SLOS appears to have the most consistent relationship with autism of any single gene disorder. Therefore, a link between cholesterol metabolism or SLOS, and autism, is suggested.
Future research into the link between autism and SLOS will focus on measuring sterols, particularly 7- and 8-DHC, in the plasma of autistic patients. This will lead to a determination of the prevalence of SLOS in autistic patients. Cholesterol concentrations in the blood will also be measured as the link between SLOS and autism may have more related to low cholesterol in the plasma rather than the presence of abnormal sterols in he plasma.
Osteogenesis Imperfecta (OI) is a genetic disorder that is characterized by frequent bone fractures with little or no trauma, hearing loss, and dentinogenesis imperfecta. There are 4 types of IO that are caused by a mutation in the COL1A1, COL1A2, CRTAP, or LEPRE1 genes. In all cases, mutations in these genes affect the production, assembly, or processing of type I collagen. The severity of OI ranges from perinatal lethality to individuals who are nearly asymptomatic.
Symptoms of Osteogenesis Imperfecta
In the most severe form, symptoms include:
- Deformed or short legs or arms
- Kyphosis (S-curved spine)
- Short stature
- Abnormal Teeth
- Fragile bones
- Loose joints or hypermobility
- Blue Sclerae
- Hearing impairment or deafness
- Bowed Legs
- Pectus carinatum (rounded, protruding chest)