Browsing Pathways

Hyperimmunoglobulinemia D syndrome, or HIDS, is a condition characterized by fevers that come and go, usually lasting 3-7 days, and other various symptoms such as rashes, vomiting, diarrhea and aphthous ulcers. These are usually noticed within the first year of a patient's life, and the highest frequency of HIDS usually occurs during childhood/adolescence. It occurs due to a mevalonate kinase deficiency inherited from both parents. In patients with this condition, the MVK gene is mutated, resulting in a lack of mevalonate kinase. Although globally this condition is rare, there are much higher instances in The Netherlands, about 1 in 350 Dutch nationals carry this mutation.

Hypercholesterolemia, also called elevated cholesterol, is an autosomal dominant disorder caused by a defective LDLR gene. The LDLR gene codes for a receptor that binds to low-density lipoprotein which are carriers of cholesterol in the blood. The mutation on the LDLR gene causes the removal of cholesterol from the bloodstream to be limited, resulting in a buildup of cholesterol in the blood. This disorder is characterized by a large accumulation of cholesterol in the blood. Symptoms of the disorder include angina, tendon xanthomas increased risk of cardiac arrest. Treatment with atorvastatin, simvastatin or rosuvastatin, in combination with a heart healthy diet and regular exercise is very effective. It is estimated that hypercholesterolemia affects 1 in 500 individuals in most countries.

Porphyria variegata (PV) is a rare inborn error of metabolism (IEM) which arises from a defective gene called PPOX. PPOX is responsible for protoporphyrinogen oxidase. A defect in this enzyme results in the build up of several compounds, including porphobilinogen, 5-aminolevulinic acid, and in feces and urine, porphyrin and coproporphyrin. Of the wide range of symptoms which present themselves in affected individuals, some include abdominal pain, vomiting, and diarrhea. As well as seizures, hallucinations and skin sensitivity to light. Indeed, the skin sensitivity can be so extreme that skin pigmentation changes, scarring and blistering and even hair growth can ensue on exposed areas.

Beta-ureidopropionase deficiency (Beta Alanine-Synthase Deficiency, UPB1, BUP1) is an autosomal recessive disease caused by mutations in the UPB1 gene which codes for beta-ureidopropionase. A deficiency in this enzyme results in accumulation of N-carbamyl-beta-amino acids. Symptoms include hypotonia, dystonic movements, scoliosis, microcephaly, and severe developmental delay.

D-Glyceric aciduria is an extremely rare inherited inborn error of metabolism (IEM) of serine and fructose metabolism. It is an autosomal recessive disorder that is caused by a defect in the D-glycerate kinase (GLYCTK) gene. GLYCTK codes for D-glycerate kinase, an enzyme that is responsible for phosphorylating D-glyceric acid into phosphoglycerate. D-Glycerate kinase is an enzyme that participates in 3 metabolic pathways: (1) serine/glycine/threonine metabolism, (2) glycerolipid metabolism, and (3) glyoxylate-dicarboxylate metabolism (which is a minor pathway in fructose metabolism). Defects in the enzyme will lead to accumulations of D-glyceric acid in tissues and biofluids. D-Glyceric aciduria was first described in 1974 and is characterized by elevated levels of D-glyceric acid in the urine. Clinical symptoms of D-glyceric aciduria are highly variable. Some patients have neurological symptoms, with severe mental retardation, seizures, microcephaly, and sometimes early death, whereas others have a mild phenotype with only mild speech delay or even normal development.

Fanconi-Bickel Syndrome is a syndrome first described in 1949, by Falconi and Bickel, where the body is missing a glucose transport, causing glycogen stores to accumulate and cause symptoms such as swelling of the liver and spleen, rickets, and failure to thrive. Hypoglycemia may occur in between meals for patients with this condition. This condition happens through a mutation on the SLC2A2 gene, which has the instructions on how to create a protein which is the glucose-transporter protein 2 (GLUT2). GLUT2 does not work properly when there is an SLC2A2 gene mutation, which makes glycogen build up in the liver and kidneys, causing the symptoms of this condition.

Apparent mineralocorticoid excess (AME), also known as cortisol 11-beta-ketoreductase deficiency, is an extremely rare inborn error of metabolism (IEM) and autosomal recessive disorder of the steroidogenesis pathway. It is caused by a mutation in the HSD11B2 gene which encodes for corticosteroid 11-beta-dehydrogenase isozyme 2, and enzyme that converts cortisol to cortisone in the cell. Without this enzyme being functional, an accumulation of tetrahydrocortisol builds up, while tetrahydrocortisone levels dissipate. AME is characterized excessive thirst and urination, and along with this, symptoms include low levels of aldosterone, failure to thrive and hypertension. Treatment with corticoids that suppress the secretion of cortisol within the body can affect blood pressure and aldosterone levels. Antihypertensive agents are also effective. It is estimated that AME affects less than 1 in 1,000,000 individuals, with less than 100 reported cases as of 2019.

Sarcosinemia (SAR), also known as hypersarcosinemia, sarcosine dehydrogenase complex deficiency, SARDH deficiency, SARDHD or SARD deficiency, is an autosomal recessive metabolic disorder leading to increased levels of the amino acid sarcosine in blood plasma, as well as increased levels of sarcosine excreted in urine. SAR can be caused by a mutation, either homozygous or compound heterozygous, in the SARDH gene which codes for the sarcosine dehydrogenase enzyme. This enzyme converts sarcosine to glycine, and its absence leads to an increase in the amount of sarcosine in the body. It can also potentially be caused by a lack of folate, as folate is used in the sarcosine dehydrogenase reaction, and even with a working enzyme, the lack of substrates can prevent the conversion from occurring, leading to the same effects. The condition has been associated with mental and motor retardation, visual impairment, however other cases have been detected with no mental or physical abnormalities other than increased sarcosine levels, so it is possible that the defect is benign, or that there exist some phenotypes that are more severe than others, or unknown disorders present in the cases showing symptoms. Sarcosine can be formed from a series of reactions starting with trimethylglycine. This, along with homocysteine, react using betaine-homocysteine S-methyltransferase to form L-methionine, as well as dimethylglycine. The dimethylglycine then enters the mitochondrial matrix, and interacts with dimethylglycine dehydrogenase along with a water molecule, forming formadehyde and sarcosine. Sarcosine can also be formed in a reversible reaction from S-adenosylmethionine and glycine, using glycine N-methyltransferase as the enzyme, and forming S-adenosylhomocysteine as another product. Normally, sarcosine can interact with sarcosine dehydrogenase in the mitochondria, forming both formaldehyde and glycine. However, in this disorder, the gene encoding sarcosine dehydrogenase has been mutated and the protein is not produced, preventing this reaction from occurring. This leads to an increased concentration of sarcosine, which leads to the effects of the condition.

Nonketotic hyperglycinemia (GCE) is a rare inborn error of metabolism (IEM) and autosomal recessive disorder caused by a defective GLDC gene. GLDC encodes for the enzymes involved in the conversion of glycine to CO2, NH3 and hydroxymethyltetrahydrofolic acid. Most patients have abnormally low oxalate excretion in the urine. Other symptoms start presenting in the first few days of life and include lethargy, hypotonia, and myoclonic jerks, and progressing to apnea. GCE often leads to death, and those who regain spontaneous respiration develop intractable seizures and profound mental retardation. Currently there is no cure for Nonketotic hyperglycinemia therefore treatment involves managing symptoms. Frequency for Nonketotic hyperglycinemia has not been documented worldwide.

5-Oxoprolinuria (5-Oxoprolinase deficiency) is a result of a defect in the gamma-glutamyl cycle due to either 5-oxoprolinase or glutathione synthetase deficiency. In the case of glutathione synthetase deficiency, the glycine is not incorporated into gamma-glutamylcysteine. In the case of 5-oxoprolinase, however, pyroglutamic acid accumulates. Symptoms include anemia, mental retardation, metabolic acidosis, respiratory distress and urolithiasis.