Browsing Pathways

Hereditary folate malabsorption, also known as folic acid transport defect, is an extremely rare inborn error of metabolism (IEM) and autosomal recessive disorder of the folate metabolism pathway. It is caused by a defect in the SLC46A1 gene that encodes the proton-coupled folate transporter protein which is responsible for folate uptake from the intestines. Hereditary folate malabsorption is characterized by low concentrations of folate in the serum and cerebrospinal fluid. Symptoms include feeding difficulties and failure to thrive and anemia, as well as potential neurological issues such as seizures and developmental delays. When infants are born with hereditary folate malabsorption, there are initially few signs, as folate is provided across the placenta, but after birth, folate absorption is inhibited and these symptoms begin to be exhibited. Treatment for hereditary folate malabsorption includes intramuscular or oral doses of reduced folates to bring cerebrospinal fluid folate levels to a normal range, as well as blood transfusions if severe anemia is present. It is estimated that hereditary folate malabsorption affects less than 1 in 1,0000,000 people, with only approximately 30 reported cases.

Lactose intolerance is a condition in which the body does not support the ingestion of lactose through the consumption of milk, cheese, and other dairy products. This intolerance occurs due to the lack of the enzyme intestinal lactase, which is an enzyme found in newborns. The frequency of this enzyme declines rapidly after the child stops breastfeeding. Lactase deficiency is most prevalent in Asia, Africa and Indigenous populations in North and South America. The symptoms of lactose intolerance include diarrhea, bloating, abdominal pain and excessive flatus. The cause of these symptoms is the processing of the ingested lactose being fermented by intestinal bacteria instead of in the small intestine, where lactose is meant to be processed.

Homocystinuria, Cystathionine beta-Synthase Deficiency, also known as homocystinuria, is a inherited disorder of amino acid methionine metabolism caused by a defective cystathionine beta-Synthase. Cystathionine beta-Synthase catalyzes the conversion of homocysteine and L-Serine into L-Cystathionine which is the substrate of cystathionine gamma-lyase. This disorder is characterized by a large accumulation of homocysteine in the cell. Symptoms of the disorder include thromboembolism, ectopia lentis and/or severe myopia, skeletal system deficiency and developmental delay. Treatment with homocystinuria aims at correct the biochemical abnormalities through disorder management (e.g. surveillance, circumstances to avoid, prevention of primary manifestations, etc.

The rare genetic disorder, Xanthinuria (also referred to as xanthine oxidase deficiency) results from a deficiency of the enzyme xanthine oxidase. This enzyme deficiency causes the accumulation of: xanthine in the plasma, uric acid in serum or hypoxanthine, uric acid and xanthine in the urine. The disorder has symptoms including arthralgia, hematuria, mental retardation, stomatisis, and urolithiasis.

Adenine phosphoribosyltransferase deficiency, which is also known as APRTD or APRT deficiency, is a rare inherited inborn error of metabolism (IEM) leading to the recurrent formation of kidney stones. It is an autosomal recessive disorder associated with a mutation in the enzyme adenine phosphoribosyltransferase (APRT). APRT is involved in the nucleotide salvage pathway, which provides an alternative, and energetically more efficient route to nucleotide biosynthesis in humans and most other animals. A defect in this enzyme can lead to the accumulation of the insoluble purine known as 2,8-dihydroxyadenine. In particular, when APRT has reduced or nonexistent activity, adenine accumulates which is then degraded by xanthine dehydrogenase to 2,8-dihydroxyadenine (DHA). 2,8-Dihydroxyadenine is a derivative of adenine which accumulates in 2,8 dihydroxyadenine urolithiasis (kidney stones). Kidney and urinary tract stones can obstruct the urinary tract, resulting in pain and difficulty urinating. If left untreated, the condition can eventually produce kidney failure. APRTD was first diagnosed in 1976. There are two categories of APRTD: type I involves a complete loss of the APRT function while type II involves a partial loss and is mostly found in Japan. APRT deficiency is estimated to affect 1 in 27 000 people in Japan. APRTD is rarer in Europe, where it affects 1 in 50 000 to 100 000 people. A diagnosis of APRTD can be made by analyzing kidney stones or measuring DHA concentrations in urine. APRTD is treatable with regular doses of allopurinol, which inhibits xanthine dehydrogenase activity. APRTD can also be treated with a low-purine diet and a high fluid intake.

Salla disease, also called sialic acid storage disease, is a rare inborn error of metabolism (IEM) and autosomal recessive disorder of lysosomal storage caused by a defective SLC17A5 gene. SLC17A5 codes for the lysosomal transporter sialin which exports sialic acid from the lysosome into the cytoplasm. This disorder is characterized by a large accumulation of sialic acid in the urine. Symptoms of the disorder include seizures, intellectual disability, developmental delay, nystagmus, hypotonia, ataxia, spasticity, and athetosis. There are three forms of Salla disease: infantile free sialic acid storage disease (ISSD), Salla disease, and intermediate severe Salla disease. Since there is currently no cure for Salla disease, treatment involves managing the disorder's symptoms. Salla disease has been reported in approximately 150 people (mostly from Finland and Sweden) and ISSD has been reported in a few dozen infants.

Lesch-Nyhan Syndrome is a syndrome identified through its neurological, behavioural metabolic impact. It is characterized by a mental deficit and self-mutilation, accompanied with an overproduction of uric acid. A mutation of the HPRT1 gene are responsible for this condition, as they cause the enzyme hypoxanthine phosphoribosyltransferase 1 to be present in extremely low levels or absent altogether. This causes an overproduction of uric acid as the purines are not recycled, but only broken down. This gene is also connected to dopamine production, which a lack of causes smooth muscle function to suffer, resulting in dystonia, ballismus and chorea. Patients are usually unable to walk, and the connection between a lack of hypoxanthine phosphoribosyltransferase 1 and the behavioural abnormalities associated with this condition are unknown.

Pyruvate dehydrogenase complex deficiency results from a mutation in the E1-alpha polypeptide gene (PDHA1). PDHA1 encodes the pyruvate dehydrogenase complex (PDC) a critical complex that converts pyruvate from glycolysis to acetyl CoA for the citric acid cycle. This conversion step links glycolysis and the citric acid cycle. A defect in this complex causes accumulation of lactate and pyruvate in the blood; lactate and pyruvic acid in the spinal fluid; and lactate in the urine. Symptoms include lactic and metabolic acidosis, motor retardation, dystonia, growth and mental retardation, and respiratory distress.

Pyruvate kinase deficiency is a genetic disorder. It affects red blood cells in the body. Patients are affected by a condition called chronic hemolytic anemia, which is where red blood cells undergo hemolysis before they are meant to which causes anemia in the patient. Symptoms of this condition can include jaundice, fatigue, dyspnea and splenomegaly. Gallstones are also common to patients with this disorder. This disorder is diagnosed through genetic testing. In mild cases, no treatment is required. Patients with more severe cases may require blood transfusions, and occasionally the spleen is removed to aid with the reduction of red blood cell destruction.

17-beta hydroxysteroid dehydrogenase III deficiency, also known as 17-KSR deficiency or male pseudohermaphroditism with gynecomastia (MPH), is as rare inborn error of metabolism (IEM) and autosomal recessive disorder of the androgen and estrogen metabolism pathway. It is caused by a mutation in the HSD17B3 gene, which encodes the enzyme testosterone 17-beta-dehydrogenase 3, which is responsible for catalyzing the reversible formation of androstenedione from testosterone. This leads to an accumulation of androstenedione and dehydroepiandrosterone in the body, as well as a lack of testosterone produced. 17-KSR deficiency is characterized by an absence of testosterone in the testis until puberty, where testosterone is produced outside of the gonads. Symptoms include infertility and external female genitalia until puberty, when secondary male sex characteristics occur, as well as gynecomastia. Due to this, many individuals with this disorder are raised as female despite being genetically male, until puberty. Treatment can include removal of testes before puberty, preventing any masculinization at puberty, as well as surgical treatment of genitalia. However, there is no known treatment for restoring the fertility of affected individuals. It is estimated that 17-KSR deficiency affects 1 in 150,000 individuals in The Netherlands, without much information for the rest of the world.