Biomedical subjects

K Michael Gibson

Publications and source records attributed to K Michael Gibson.

36 records · Page 2Linked to original sources

PubMed2004

From the street to the brain: neurobiology of the recreational drug gamma-hydroxybutyric acid.

gamma-Hydroxybutyric acid (GHB) is a short-chain fatty acid that occurs naturally in the mammalian brain and is formed primarily from the precursor gamma-aminobutyric acid (GABA). The properties of GHB suggest that it has a neuromodulatory role in the brain and has the ability to induce several pharmacological and behavioral effects. GHB has been used clinically as an anesthetic and to treat alcoholism and narcolepsy. Furthermore, GHB has emerged recently as a major recreational drug of abuse. GHB appears to have dual mechanisms of action in the brain. Biochemical data suggest that the intrinsic neurobiological activity of GHB might be mediated through the GHB receptor, which is separate and distinct from the GABA(B) receptor. However, many of the pharmacological and clinical effects of exogenously administered GHB, including the properties of addiction, tolerance, withdrawal and intoxication, are probably mediated via the GABA(B) receptor, where GHB might act both directly as a partial agonist and indirectly through GHB-derived GABA.

Animals↗

PubMed2004

Liver-directed adenoviral gene transfer in murine succinate semialdehyde dehydrogenase deficiency.

Murine succinate semialdehyde dehydrogenase (SSADH) deficiency (OMIM 271980; EC 1.2.1.24), a model of the corresponding human disorder, displays 100% mortality at weeks 3-4 of life, associated with lethal tonic-clonic seizures. The biochemical hallmark, gamma-hydroxybutyrate (GHB), accumulates in both human and murine disorders. In the current study we evaluated rescue of the murine model with liver-directed gene therapy using the E1-deleted adenoviral vector AD:pAD-RSV-humanSSADH. Our working hypotheses were: (1) liver expresses considerable SSADH activity and therefore represents a major source of GHB output, (2) correction of liver enzyme deficiency will reduce GHB load both peripherally and in the central nervous system, and (3) SSADH expression will improve survival. SSADH(-/-) and SSADH(+/+) mice were treated under two protocols: (A) intraperitoneal injection of 10(8)-10(11) viral particles by day 10 of life or (B) retro-orbital injection of 10(11) viral particles at day 13 of life. Intravenous administration was prohibited by the small size and fragility of the mice. Maximal survival (39%; P<0.001) was achieved with intraperitoneal administration (10(8) particles) at day 10; intraperitoneal (10(10) and 10(11) particles) and retro-orbital administration (10(11) particles) yielded lower survival of 11-25% (P<0.02). Under both protocols, the maximal hepatic SSADH enzyme activity was approximately 20% of SSADH(+/+) liver activity (retro-orbital > ip). At various time points postinjection, ip-treated animals (10(8) viral particles) demonstrated upward of 80% reduction in liver GHB concentrations, with little impact on brain or serum GHB levels except at 48-72 h posttreatment (approximately 50% reduction for both tissues). Accordingly, we harvested retro-orbitally treated animals at 72 h and observed significant reductions of 60-70% for GHB in liver, kidney, serum, and brain extracts. Histochemical analysis of liver from retro-orbitally treated mutants demonstrated substantial SSADH staining, but with variability both within tissues and between animals. Our studies provide proof-of-principle that liver-mediated gene therapy has efficacy in treating SSADH deficiency and that hepatic tissue contributes significantly to the pool of GHB within the CNS.

Adenoviridae↗

PubMed2004

Clinical aspects of the disorders of GABA metabolism in children.

PURPOSE OF REVIEW: There has been increased recognition of the pediatric neurotransmitter disorders. This review focuses on the clinical disorders of GABA metabolism. RECENT FINDINGS: The known clinical disorders of GABA metabolism are pyridoxine dependent epilepsy, GABA-transaminase deficiency, SSADH deficiency, and homocarnosinosis. Pyridoxine dependent epilepsy is diagnosed clinically but potentially more common presentations, with later and atypical features, widen the spectrum. No gene locus has been confirmed; the pathophysiology may involve alterations in PLP transport, binding to GAD, or other PLP-dependent pathways. SSADH deficiency is associated with developmental delay, prominent language deficits, hypotonia, ataxia, hyporeflexia, and seizures. Increased detection is reported when specific ion monitoring is used for GHB on urine organic acids. The most consistent MRI abnormality is increased signal in the globus pallidus. MR spectroscopy has demonstrated the first example of increased endogenous GABA in human brain parenchyma in this disorder. GABA-transaminase deficiency and homocarnosinosis appear to be very rare but require CSF for detection, thus allowing for the possibility that these entities, as in the other pediatric neurotransmitter disorders, are underrecognized. SUMMARY: The disorders of GABA metabolism require an increased index of clinical suspicion. Pyridoxine dependent epilepsy is a treatable condition with a potentially widening clinical spectrum, but with a prognosis dependent on early intervention. SSADH deficiency has a heterogeneous spectrum and requires careful urine organic acid testing for screening, followed by enzymatic confirmation allowing appropriate prognostic and genetic counseling.

4-Aminobutyrate Transaminase↗

PubMed2004

Gamma-hydroxybutyric acid: neurobiology and toxicology of a recreational drug.

gamma-Hydroxybutyric acid (GHB) is a short-chain fatty acid that occurs naturally in mammalian brain where it is derived metabolically from gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the brain. GHB was synthesised over 40 years ago and its presence in the brain and a number of aspects of its biological, pharmacological and toxicological properties have been elucidated over the last 20-30 years. However, widespread interest in this compound has arisen only in the past 5-10 years, primarily as a result of the emergence of GHB as a major recreational drug and public health problem in the US. There is considerable evidence that GHB may be a neuromodulator in the brain. GHB has multiple neuronal mechanisms including activation of both the gamma-aminobutyric acid type B (GABA(B)) receptor, and a separate GHB-specific receptor. This complex GHB-GABA(B) receptor interaction is probably responsible for the protean pharmacological, electroencephalographic, behavioural and toxicological effects of GHB, as well as the perturbations of learning and memory associated with supra-physiological concentrations of GHB in the brain that result from the exogenous administration of this drug in the clinical context of GHB abuse, addiction and withdrawal. Investigation of the inborn error of metabolism succinic semialdehyde deficiency (SSADH) and the murine model of this disorder (SSADH knockout mice), in which GHB plays a major role, may help dissect out GHB- and GABA(B) receptor-mediated mechanisms. In particular, the mechanisms that are operative in the molecular pathogenesis of GHB addiction and withdrawal as well as the absence seizures observed in the GHB-treated animals.

Dopamine↗

PubMed2003

Significant behavioral disturbances in succinic semialdehyde dehydrogenase (SSADH) deficiency (gamma-hydroxybutyric aciduria).

We report two adult patients with succinic semialdehyde dehydrogenase deficiency, manifesting as gamma-hydroxybutyric aciduria. For both, the clinical presentation included significant behavioral disturbances and psychosis (hallucinations, disabling anxiety, aggressive behavior, and sleep disorder), leading to multiple therapeutic attempts. Intervention with benzodiazepines appeared most efficacious, resulting in decreased aggression and agitation and improvement in anxiety. A review of 56 published and unpublished studies of SSADH-deficient patients revealed that 42% manifested behavioral disturbances, whereas 13% (predominantly adults) displayed psychotic symptomatology. To explore the potential biochemical basis of these behavioral abnormalities, we studied cerebrospinal fluid derived from 13 patients, which revealed significantly elevated GHB (65- to 230-fold), high free and total GABA (up to threefold), and low glutamine. Although within the control range, homovanillic and 5-hydroxyindoleacetic acids (end products of dopamine and serotonin metabolism, respectively) showed a significant linear correlation with increasing GHB concentration, suggesting enhanced dopamine and serotonin turnover. We conclude that elevated GABA combined with low glutamine suggest disruption of the glial-neuronal glutamine/GABA/glutamate shuttle necessary for replenishment of neuronal neurotransmitters, whereas altered dopamine and serotonin metabolism may be causally linked to the hyperkinetic movement disorders and behavioral disturbances seen in SSADH-deficient patients.

Adult↗

PubMed2003

Murine succinate semialdehyde dehydrogenase deficiency.

Inherited succinic semialdehyde dehydrogenase (SSADH) deficiency (gamma-hydroxybutyric aciduria) is one of the few neurogenetic disorders of GABA metabolism, and one in which tonic-clonic seizures associate with increased central nervous system GABA and gamma-hydroxybutyrate (GHB). To explore pathomechanisms and develop new preclinical treatment approaches, we developed a murine knockout model of SSADH deficiency. In the absence of intervention, SSADH(-/-) mice suffer 100% mortality at week 3 to 4 of life from generalized tonic-clonic seizures. In this report, we summarize earlier studies indicating disruption of the GABA/glutamine axis in SSADH(-/-) mouse brain, effective pharmacotherapeutic approaches, preliminary gene-therapy results, and electrophysiological analyses of mutant mice. We also present new evidence for oxidative stress in SSADH(-/-) mice, significant alterations of dopamine metabolism, and abnormal neurosteroid levels in brain, potentially implicating the GABA(A) receptor in pathogenesis. In SSADH deficiency, the accumulation of two neuroactive species, GABA and GHB, is significant because GABA is one of the earliest transmitters expressed in mammals, with key roles in synaptogenesis and myelination, whereas GHB displays a vast array of pharmacological actions. The SSADH(-/-) mouse may represent a useful model in which to explore the effect of GABA and GHB accumulation on central nervous system development and function.

Aldehyde Oxidoreductases↗

PubMed2003

Succinic semialdehyde dehydrogenase deficiency in children and adults.

Succinic semialdehyde dehydrogenase deficiency is a rare disorder of the degradation pathway of gamma-aminobutyric acid. The disorder is detected when 4-hydroxybutyric aciduria is present on urine organic acid analysis, and is subsequently confirmed by enzyme measurement on leucocytes. The disorder has been identified in approximately 350 individuals worldwide. We review the clinical features in 60 patients. The most common characteristics are developmental delay maximally involving expressive language, hypotonia, mental retardation, ataxia, and behavioral problems. Seizures occur in approximately half of patients, and include tonic-clonic, absence, and myoclonic seizures, including status epilepticus. Electroencephalographic findings are background slowing and generalized and focal epileptiform discharges. Magnetic resonance imaging typically reveals increased T2-weighted signal of the globus pallidus bilaterally, with variable involvement of white matter and the cerebellar dentate nucleus. Preliminary human cerebrospinal fluid measurements are consistent with neurometabolic aberrations documented in the murine animal model, with elevations in gamma-aminobutyric acid, gamma-hydroxybutyrate, and homocarnosine, and low glutamine. Succinic semialdehyde dehydrogenase deficiency may be an underrecognized neurometabolic disorder with a nonspecific and wide phenotypic spectrum, and carries implications for a comprehensive fundamental understanding of interrelations between multiple neurotransmitter systems.

Adult↗

PubMed2003

Magnetic resonance spectroscopy of neurotransmitters in human brain.

Magnetic resonance spectroscopy (MRS) is a noninvasive method that permits measurement of the concentration of specific biochemical compounds in the brain and other organ systems in precisely defined regions guided by MR imaging (MRI). Recently, MRS methods have been developed to measure specific neurotransmitters in the brain. More advanced MRS methods have been developed to measure the synthesis rates and turnover of specific neurotransmitters. These turnover rates can provide measures of brain metabolism similar to radioisotope techniques. Also, investigations of the relationship of brain metabolism and specific neurotransmitter systems are now possible using MRS. Here, we review the MRS techniques and studies of neurotransmitters in the human brain. A discussion of the potential use of these techniques in the context of certain pediatric neurotransmitter disorders will be presented.

Brain Chemistry↗

PubMed2003

Monitoring of 4-hydroxybutyric acid levels in body fluids during vigabatrin treatment in succinic semialdehyde dehydrogenase deficiency.

We report the successful treatment using low-dose vigabatrin (21.5-34 mg/kg/day) of a 10-year-old girl with succinic semialdehyde dehydrogenase (SSADH) deficiency We verified that 4-hydroxybutyric acid (GHB) concentrations in serum, cerebrospinal fluid, and urine continuously decreased in parallel with significant clinical improvement. Our results suggest that GHB quantification in physiological fluids may be a useful laboratory parameter for monitoring efficacy of vigabatrin treatment in SSADH deficiency.

Aldehyde Oxidoreductases↗

PubMed2003

Mutations in the AUH gene cause 3-methylglutaconic aciduria type I.

The conversion of 3-methylglutaconyl-CoA to 3-hydroxy-3-methylglutaryl-CoA is the only step in leucine catametabolism yet to be characterized at enzyme and DNA levels. The deficiency of the putative mitochondrial enzyme 3-methylglutaconyl-CoA hydratase associates with the rare organic aciduria 3-methylglutaconic aciduria type I (MGA1), but neither the enzyme nor its gene have been described in any organism. Here we report that human 3-methylglutaconyl-CoA hydratase is identical with a previously described RNA-binding protein (designated AUH) possessing enoyl-CoA hydratase activity. Molecular analyses in five patients from four independent families revealed homozygosity or compound heterozygosity for mutations in the AUH gene; most mutations are predicted to completely abolish protein function. Mutations identified include c.80delG, R197X, IVS8-1G>A, A240V, and c.613_614insA. Clinical severity of MGA1 in published patients has been quite variable. Included in the present study is an additional patient with MGA1 who was detected by neonatal screening and has remained asymptomatic up to his present age of 2 years. The boy is homozygous for an N-terminal frameshift mutation in the AUH gene. Complete absence of 3-methylglutaconyl-CoA hydratase/AUH appears to be compatible with normal development in some cases. Further work is required to identify external or genetic factors associated with development of clinical problems in patients with MGA1.

Amino Acid Metabolism, Inborn Errors↗

PubMed2003

Mutational spectrum of the succinate semialdehyde dehydrogenase (ALDH5A1) gene and functional analysis of 27 novel disease-causing mutations in patients with SSADH deficiency.

Succinate semialdehyde dehydrogenase (SSADH; ALDH5A1) deficiency, a rare metabolic disorder that disrupts the normal degradation of GABA, gives rise to a highly heterogeneous neurological phenotype ranging from mild to very severe. The nature of the mutation has so far been reported in patients from six families world wide and eight different mutations were described. Here we report the mutational spectrum in 48 additional unrelated families of different geographic origin. We detected 27 novel mutations at the cDNA level, of which 26 could be attributed to changes at the genomic level. Furthermore, six mutations were detected that did not strongly affect SSADH activity when expressed in HEK 293 cells and are considered nonpathogenic allelic variants. Twenty of the mutations were only found in one family. The spectrum of disease-causing mutations from all patients sequenced thus far consists of 25 point mutations, four small insertions, and five small deletions. Seven of these mutations affect splice junctions, seven are nonsense mutations, and 12 are missense mutations. Although there were no mutational hotspots or prevalent mutations responsible for a significant number of cases, 14 out of 37 (38%) of the missense alleles were present in exon 4 or 5. With one exception, the missense mutations we consider to be causative of SSADH deficiency reduced the SSADH activity to less than 5% of the normal activity in our in vitro expression system. This indicates that residual expression is not likely to be an important factor contributing to the large phenotypic differences observed among different families and even among siblings, suggesting that other modifying factors are of great importance in disease pathology.

Aldehyde Oxidoreductases↗

PubMed2003

Oxidation of 4-hydroxy-2-nonenal by succinic semialdehyde dehydrogenase (ALDH5A).

Elevated levels of 4-hydroxy-trans-2-nonenal (HNE) are implicated in the pathogenesis of numerous neurodegenerative disorders. Although well-characterized in the periphery, the mechanisms of detoxification of HNE in the CNS are unclear. HNE is oxidized to a non-toxic metabolite in the rat cerebral cortex by mitochondrial aldehyde dehydrogenases (ALDHs). Two possible ALDH enzymes which might oxidize HNE in CNS mitochondria are ALDH2 and succinic semialdehyde dehydrogenase (SSADH/ALDH5A). It was previously established that hepatic ALDH2 can oxidize HNE. In this work, we tested the hypothesis that SSADH oxidizes HNE. SSADH is critical in the detoxification of the GABA metabolite, succinic semialdehyde (SSA). Recombinant rat SSADH oxidized HNE and other alpha,beta-unsaturated aldehydes. Inhibition and competition studies in rat brain mitochondria showed that SSADH was the predominant oxidizing enzyme for HNE but only contributed a portion of the total oxidizing activity in liver mitochondria. In vivo administration of diethyldithiocarbamate (DEDC) effectively inhibited (86%) ALDH2 activity but not HNE oxidation in liver mitochondria. The data suggest that a relationship between the detoxification of SSA and the neurotoxic aldehyde HNE exists in the CNS. Furthermore, these studies show that multiple hepatic aldehyde dehydrogenases are able to oxidize HNE.

Aldehyde Dehydrogenase↗

PubMed2003

Mevalonate kinase deficiency: enlarging the clinical and biochemical spectrum.

OBJECTIVE: Mevalonic aciduria as a result of mevalonate kinase deficiency is an inborn error of cholesterol biosynthesis characterized by dysmorphology, psychomotor retardation, progressive cerebellar ataxia, and recurrent febrile crises, usually manifesting in early infancy, accompanied by hepatosplenomegaly, lymphadenopathy, arthralgia, and skin rash. The febrile crises are similar to those observed in hyperimmunoglobulinemia D and periodic fever syndrome (HIDS). Pathogenic mutations in the mevalonate kinase gene in both disorders have demonstrated a common genetic basis. Our aim was to describe the clinical picture of adolescent patients with mevalonate kinase deficiency and to expand the clinical and biochemical spectrum of mevalonate kinase deficiency, particularly with regard to HIDS. METHODS: We report the clinical history and biochemical findings of 3 patients with mevalonic aciduria. RESULTS: In 2 siblings with mevalonic aciduria, a 15-year-old girl and a 14-year-old boy, the phenotype shifted with age. Ataxia has become the predominant clinical manifestation, whereas the febrile attacks occur less frequently but as yet have not disappeared. Both of them show marked elevations of immunoglobulin D (IgD). Psychomotor development is retarded but not regressive. Short stature developed in both patients. Additional findings include the development of retinal dystrophy and cataracts in both of them. The third patient is a 6-year-old boy who presented at the age of 5 years with cerebellar ataxia and retinal dystrophy. He is different from all known patients with mevalonic aciduria because of the mild neurologic involvement and because he has never developed febrile crises. In addition, levels of IgD were repeatedly normal. CONCLUSION: The clinical and biochemical spectrum of patients with mevalonic aciduria is heterogeneous. Manifestations of the disease seem to be age dependent, as evident from this first report of adolescent patients. In patients who survive infancy, short stature, ataxia caused by cerebellar atrophy, and ocular involvement with retinal dystrophy become predominant findings. Recurrent febrile crises seem to diminish with increasing age and may not even be an obligatory finding. Elevation of IgD is most likely a secondary phenomenon that seems to be linked to recurrent febrile crises.

Adolescent↗

PubMed2002

Structure of human succinic semialdehyde dehydrogenase gene: identification of promoter region and alternatively processed isoforms.

Mitochondrial NAD(+)-dependent succinic semialdehyde dehydrogenase (ALDH5A1, SSADH) represents the last enzyme in the GABA catabolism and irreversibly oxidizes SSA to succinate. In human, SSADH deficiency results in 4-hydroxybutyric aciduria, an autosomal recessive disorder due to an accumulation of GABA and 4-hydroxybutyric acid in the CNS. We already identified SSADH gene on human chromosome 6p22 and characterized the coding region. Furthermore, we described the first two mutations causing the disease. We report here the complete cDNA and genomic structure of the gene. A single transcription start site was identified by RNase protection 122 bp upstream of the ATG. EST database search and reporter gene constructs of the 3(') genomic region showed that the two major SSADH mRNA isoforms are due to alternative polyadenylation sites. The two mRNAs of 1827 and 5225 nt were analyzed for differential stability and translation efficiency. The analysis of mRNA turnover showed that both SSADH transcripts are equally stable. Similarly, a measurement of polysomal association capability of the two GFP-SSADH reporter mRNAs (containing the 3' UTR regions of the two SSADH mRNAs) did not reveal any difference. However, we cannot exclude the fact that differential properties could be restricted to particular physiological conditions and/or specific tissues. We have also identified an alternatively spliced small exon, which may lead to a novel isoform of the enzyme. Furthermore, we report here on naturally occurring missense variants, which may significantly contribute to inter-individual variation of SSADH activity, possibly influencing GABA and GHB endogenous levels.

3' Untranslated Regions↗

PubMed2002

Therapeutic intervention in mice deficient for succinate semialdehyde dehydrogenase (gamma-hydroxybutyric aciduria).

Therapeutic intervention for human succinic semialdehyde dehydrogenase (SSADH) deficiency (gamma-hydroxybutyric aciduria) has been limited to vigabatrin (VGB). Pharmacologically, VGB should be highly effective due to 4-aminobutyrate-transaminase (GABA-transaminase) inhibition, lowering succinic semialdehyde and, thereby, gamma-hydroxybutyric acid (GHB) levels. Unfortunately, clinical efficacy has been limited. Because GHB possesses a number of potential receptor interactions, we addressed the hypothesis that antagonism of these interactions in mice with SSADH deficiency could lead to the development of novel treatment strategies for human patients. SSADH-deficient mice have significantly elevated tissue GHB levels, are neurologically impaired, and die within 4 weeks postnatally. In the current report, we compared oral versus intraperitoneal administration of VGB, CGP 35348 [3-aminopropyl(diethoxymethyl)phosphinic acid, a GABA(B) receptor antagonist], and the nonprotein amino acid taurine in rescue of SSADH-deficient mice from early death. In addition, we assessed the efficacy of the specific GHB receptor antagonist NCS-382 (6,7,8,9-tetrahydro-5-[H]benzocycloheptene-5-ol-6-ylideneacetic acid) using i.p. administration. All interventions led to significant lifespan extension (22-61%), with NCS-382 being most effective (50-61% survival). To explore the limited human clinical efficacy of VGB, we measured brain GHB and gamma-aminobutyric acid (GABA) levels in SSADH-deficient mice receiving VGB. Whereas high-dose VGB led to the expected elevation of brain GABA, we found no parallel decrease in GHB levels. Our data indicate that, at a minimum, GHB and GABA(B) receptors are involved in the pathophysiology of SSADH deficiency. We conclude that taurine and NCS-382 may have therapeutic relevance in human SSADH deficiency and that the poor clinical efficacy of VGB in this disease may relate to an inability to decrease brain GHB concentrations.

Aldehyde Oxidoreductases↗

PubMed2002

Maleylacetoacetate isomerase (MAAI/GSTZ)-deficient mice reveal a glutathione-dependent nonenzymatic bypass in tyrosine catabolism.

In mammals, the catabolic pathway of phenylalanine and tyrosine is found in liver (hepatocytes) and kidney (proximal tubular cells). There are well-described human diseases associated with deficiencies of all enzymes in this pathway except for maleylacetoacetate isomerase (MAAI), which converts maleylacetoacetate (MAA) to fumarylacetoacetate (FAA). MAAI is also known as glutathione transferase zeta (GSTZ1). Here, we describe the phenotype of mice with a targeted deletion of the MAAI (GSTZ1) gene. MAAI-deficient mice accumulated FAA and succinylacetone in urine but appeared otherwise healthy. This observation suggested that either accumulating MAA is not toxic or an alternate pathway for MAA metabolism exists. A complete redundancy of MAAI could be ruled out because substrate overload of the tyrosine catabolic pathway (administration of homogentisic acid, phenylalanine, or tyrosine) resulted in renal and hepatic damage. However, evidence for a partial bypass of MAAI activity was also found. Mice doubly mutant for MAAI and fumarylacetoacetate hydrolase (FAH) died rapidly on a normal diet, indicating that MAA could be isomerized to FAA in the absence of MAAI. Double mutants showed predominant renal injury, indicating that this organ is the primary target for the accumulated compound(s) resulting from MAAI deficiency. A glutathione-mediated isomerization of MAA to FAA independent of MAAI enzyme was demonstrated in vitro. This nonenzymatic bypass is likely responsible for the lack of a phenotype in nonstressed MAAI mutant mice.

Acetoacetates↗

PubMedDate not supplied

Lowered DHCR7 activity measured by ergosterol conversion in multiple cell types in Smith-Lemli-Opitz syndrome.

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder of cholesterol metabolism characterized by multiple congenital anomalies and mental retardation. SLOS results from mutations in 7-dehydrocholesterol Delta7 reductase (DHCR7), the gene encoding the final enzyme involved in cholesterol biosynthesis. The resulting cholesterol deficiency and excessive 7- and 8-dehydrocholesterol (7-DHC, 8-DHC) in plasma and tissues are almost always diagnostic for SLOS. We measured DHCR7 activity in fibroblasts, amniocytes, and chorionic villi from controls, heterozygotes, and SLOS subjects. The enzyme activity (expressed as percent conversion of substrate) was significantly lower in untransformed fibroblasts from SLOS subjects (4.47%+/-0.72) compared to untransformed fibroblasts from heterozygotes (26.6%+/-4.6, p<0.01) or controls (50.6%+/-5.3, p<0.001). We also measured plasma cholesterol and 7-DHC, determined the severity score and identified DHCR7 mutations for most of the subjects. There was no significant correlation of enzyme activity with severity score, plasma cholesterol level, plasma 7-DHC level, or the 7-DHC:cholesterol ratio. We conclude that even though enzyme activity as measured by the ergosterol assay may not correlate with severity, this assay has the potential to distinguish SLOS cells from carrier or unaffected cells in a variety of cell types, and should prove useful in confirming a diagnosis in atypical cases where sterol levels are equivocal. Additionally, it may be important to measure residual enzyme activity in SLOS subjects being considered for a trial of statins, as this treatment could theoretically be detrimental in subjects with little or no DHCR7 activity. Finally, the data suggest a threshold enzyme activity of 8% conversion, below which disease occurs.

Case-Control Studies↗

PubMedDate not supplied

Potential for misdiagnosis due to lack of metabolic derangement in combined methylmalonic aciduria/hyperhomocysteinemia (cblC) in the neonate.

We report two infants with an inborn error of cobalamin (vitamin B(12)) metabolism whose clinical presentation in the first month of life strongly suggested bacterial or viral sepsis. The absence of any acute metabolic derangement (acidosis, hyperammonemia, hypoglycemia, or ketosis) in association with clinical features suggesting sepsis (lethargy, obtundation) could impede the correct diagnosis of cobalamin C (cblC) disorder. In addition, this is the first documentation of cerebrospinal fluid hyperhomocysteinemia in cblC defect that was highly increased and is likely to be associated with neurotoxicity in cblC patients.

Amino Acid Metabolism, Inborn Errors↗