Browsing Pathways

Disease Pathway Succinyl CoA: 3-Ketoacid CoA Transferase (SCOT) deficiency is a rare inherited metabolic disorder causing reduction of ketone body utilization. In normal functioning patients, ketone bodies such as Acetoacetate (AcAc) and 3‐hydroxybutyrate (3HB) are metabolized inside the liver from free fatty acids. Next, ketone bodies are transported to extrahepatic tissues via the blood stream. Once in extrahepatic tissues, SCOT converts AcAc to acetoacetyl‐CoA and T2 cleaves acetoacetyl‐CoA into acetyl‐CoA. This process is crucial for producing alternative energy sources to glucose in order to maintain blood glucose levels. Patients with SCOT deficiency have this process disturbed and ketoacidosis which is the acidification of the bloodstream due to excess ketone body accumulation, can occur. Current treatments include avoiding actions that could onset ketoacidosis such as fasting and early infusion of glucose. The severity of SCOT deficiency differs from patient to patient. Some exhibit severe genotypes where ketones are always in abundance in the body, while others could have mild genotypes with no preeminent ketosis however both could exhibit ketoacidotic episodes.

Succinic Semialdehyde Dehydrogenase (SSADH) deficiency is a rare autosomal recessive inherited disorder affecting the metabolism of γ-aminobutyric acid (GABA). With reduced GABA activity, oxidation of succinic semialdehyde (SSA) to succinic acid is impaired causing a build up of SSA and ultimately it’s downstream metabolite γ-hydroxybutyric acid (GHB). Symptoms of SSADH deficiency are primarily neuropsychiatric including developmental delays, hypotonia, expressive language impairment, seizures, difficulty coordinating movements (ataxia), decreased reflexes (hyporeflexia), and other behavioral issues. Patients with SSADH deficiency have elevated levels of GHB in urine, however this method is not a definitive diagnosis due to the potential volatilization of acidified urine and the use of GHB as a drug. Instead SSADH can be confirmed suing enzyme analysis in leukocytes and molecular genetic analysis of the Aldh5a1 gene at chromosome 6p22.

The autosomal recessive disorder Smith-Lemli-Opitz Syndrome (SLOS; SLO Syndrome; RSH; Rutledge Lethal Multiple Congenital Anomaly, Syndrome; Polydactyly, Sex Reversal, Renal Hypoplasia, and Unilobar Lung; Lethal Acrodysgenital Syndrome) is characterized by disordered steroid biosynthesis. It results from a mutation in the DHCR7 gene coding for the enzyme sterol delta-7-reducatase. This enzyme catalyzes the production of cholesterol by reducing the C7-C8 double bond of 7-dehydrocholesterol (7-DHC). SLOS causes the accumulation of 7-dehydrocholesterol and 8-dehydrocholesterol, and a decrease of cholesterol in plasma; and 3-methylglutaconic acid in urine. All patients with SLOS have mental retardation, and symptoms include ambiguous genitalia, hypotonia, microcephaly, syndactyly, limb abnormalities and deformities and polydactyly.

The autosomal recessive disorder Smith-Lemli-Opitz Syndrome (SLOS; SLO Syndrome; RSH; Rutledge Lethal Multiple Congenital Anomaly, Syndrome; Polydactyly, Sex Reversal, Renal Hypoplasia, and Unilobar Lung; Lethal Acrodysgenital Syndrome) is characterized by disordered steroid biosynthesis. It results from a mutation in the DHCR7 gene coding for the enzyme sterol delta-7-reducatase. This enzyme catalyzes the production of cholesterol by reducing the C7-C8 double bond of 7-dehydrocholesterol (7-DHC). SLOS causes the accumulation of 7-dehydrocholesterol and 8-dehydrocholesterol, and a decrease of cholesterol in plasma; and 3-methylglutaconic acid in urine. All patients with SLOS have mental retardation, and symptoms include ambiguous genitalia, hypotonia, microcephaly, syndactyly, limb abnormalities and deformities and polydactyly.

Sialuria is caused by mutation in the gene encoding uridinediphosphate-N-acetylglucosamine 2-epimerase (UDP-GlcNAc 2-epimerase, which causes an excessive synthesis of sialic acid (N-acetylneuraminic acid, NeuAc). This causes accumulation of sialic acid in the urine. Symptoms of sialuria include hepatosplenomegaly, hypotonia, frequent upper respiratory infections, gastroenteritis and seizures.

Sialuria is caused by mutation in the gene encoding uridinediphosphate-N-acetylglucosamine 2-epimerase (UDP-GlcNAc 2-epimerase, which causes an excessive synthesis of sialic acid (N-acetylneuraminic acid, NeuAc). This causes accumulation of sialic acid in the urine. Symptoms of sialuria include hepatosplenomegaly, hypotonia, frequent upper respiratory infections, gastroenteritis and seizures.

Sialidosis is a severe inherited disorder that affects many organs and tissues, including the nervous system. This disorder is divided into two types, which are distinguished by the age at which symptoms appear and the severity of features. Sialidosis type I is the less severe form of this condition. People with this condition typically develop signs and symptoms of sialidosis in their teens or twenties. Characteristic features may include sudden involuntary muscle contractions (myoclonus), distinctive red spots (cherry-red macules) in the eyes, and sometimes additional neurological findings. Sialidosis type I is caused by mutations in the NEU1 gene. Individuals with sialidosis type I have mutations that result in some functional NEU1 enzyme. The condition is inherited in an autosomal recessive pattern. It does not affect intelligence or life expectancy. There is no specific treatment for sialidosis. Management should be multidisciplinary and directed at supportive care and symptomatic relief. Overall health maintenance should be a priority, with seizure control as necessary. Myoclonic seizures often respond poorly to treatment with anticonvulsant medications

Short Chain Acyl CoA Dehydrogenase Deficiency (SCAD Deficiency) is caused by mutation in the gene encoding short-chain acyl-CoA dehydrogenase, an enzyme which normally breaks down short chain fatty acids. SCADD causes accumulation of ammonia in blood; butyrylcarnitine(C4) in plasma; adipic acid, butyrylglycine, ethylmalonic acid; hexanoylglycine and methylsuccinic acid in urine. Symptoms include hypoglycemia, hypotonia, microcephaly, failure to thrive, lactic acidosis, peripheral neuropathy, and vomiting.