A congenital disorder of glycosylation is one of several rare inborn errors of metabolism in which glycosylation of a variety of tissue proteins and/or lipids is deficient or defective. Congenital disorders of glycosylation are sometimes known as CDG syndromes. They often cause serious, sometimes fatal, malfunction of several different organ systems in affected infants. The most common sub-type is PMM2-CDG where the genetic defect leads to the loss of phosphomannomutase 2 (PMM2), the enzyme responsible for the conversion of mannose-6-phosphate into mannose-1-phosphate.
Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders characterized by impaired cortisol synthesis. It results from the deficiency of one of the five enzymes required for the synthesis of cortisol in the adrenal cortex. Most of these disorders involve excessive or deficient production of hormones such as glucocorticoids, mineralocorticoids, or sex steroids, and can alter development of primary or secondary sex characteristics in some affected infants, children, or adults. It is one of the most common autosomal recessive disorders in humans.
Congenital adrenal hyperplasia due to 17α-hydroxylase deficiency is an uncommon form of congenital adrenal hyperplasia (CAH) resulting from a mutation in the gene CYP17A1, which produces the enzyme 17α-hydroxylase. It causes decreased synthesis of cortisol and sex hormones, with resulting increase in mineralocorticoid production. Thus, common symptoms include mild cortisol deficiency, ambiguous genitalia in men or amenorrhea at puberty in women, and hypokalemic hypertension. However, partial (incomplete) deficiency often has inconsistent symptoms between patients, and affected women may be asymptomatic except for infertility.
Ornithine transcarbamylase deficiency also known as OTC deficiency is the most common urea cycle disorder in humans. Ornithine transcarbamylase, the defective enzyme in this disorder, is the final enzyme in the proximal portion of the urea cycle, responsible for converting carbamoyl phosphate and ornithine into citrulline. OTC deficiency is inherited in an X-linked recessive manner, meaning males are more commonly affected than females.
Boron, Walter F.; Boulpaep, Emile L., eds. (2017). Medical Physiology (3rd ed.). Philadelphia, PA: Elsevier. ISBN 978-1-4557-4377-3.
Sucrose intolerance or genetic sucrase-isomaltase deficiency (GSID) is the condition in which sucrase-isomaltase, an enzyme needed for proper metabolism of sucrose (sugar) and starch, is not produced or the enzyme produced is either partially functional or non-functional in the small intestine. All GSID patients lack fully functional sucrase, while the isomaltase activity can vary from minimal functionality to almost normal activity. The presence of residual isomaltase activity may explain why some GSID patients are better able to tolerate starch in their diet than others with GSID.
Sucrase-isomaltase is a bifunctional glucosidase located on the brush border of the small intestine, encoded by the human gene SI. It is a dual-function enzyme with two GH31 domains, one serving as the isomaltase, the other as a sucrose alpha-glucosidase. It has preferential expression in the apical membranes of enterocytes. The enzyme’s purpose is to digest dietary carbohydrates such as starch, sucrose and isomaltose. By further processing the broken-down products, energy in the form of ATP can be generated.
In medicine, the presence of elevated transaminases, commonly the transaminases alanine transaminase (ALT) and aspartate transaminase (AST), may be an indicator of liver dysfunction. Other terms include transaminasemia, and elevatedliver enzymes. Normal ranges for both ALT and AST vary by gender, age, and geography and are roughly 8-40 U/L. Mild transaminesemia refers to levels up to 250 U/L. Drug-induced increases such as that found with the use of anti-tuberculosis agents such as isoniazid are limited typically to below 100 U/L for either ALT or AST. Muscle sources of the enzymes, such as intense exercise, are unrelated to liver function and can markedly increase AST and ALT. Cirrhosis of the liver or fulminant liver failure secondary to hepatitis commonly reach values for both ALT and AST in the >1000 U/L range; however, many people with liver disease have normal transaminases. Elevated transaminases that persist less than six months are termed "acute" in nature, and those values that persist for six months or more are termed "chronic" in nature.
Guanidinoacetate methyltransferase deficiency is an autosomal recessive cerebral creatine deficiency that primarily affects the nervous system and muscles. It is the first described disorder of creatine metabolism, and results from deficient activity of guanidinoacetate methyltransferase, an enzyme involved in the synthesis of creatine. Clinically, affected individuals often present with hypotonia, seizures and developmental delay. Diagnosis can be suspected on clinical findings, and confirmed by specific biochemical tests, brain magnetic resonance spectroscopy, or genetic testing. Biallelic pathogenic variants in GAMT are the underlying cause of the disorder. After GAMT deficiency is diagnosed, it can be treated by dietary adjustments, including supplementation with creatine. Treatment is highly effective if started early in life. If treatment is started late, it cannot reverse brain damage which has already taken place.
B-cell receptor-associated protein 31 is a protein that in humans is encoded by the BCAP31 gene.
PNGase also known as N-glycanase 1 or peptide-N(4)-(N-acetyl-beta-glucosaminyl)asparagine amidase is an enzyme that in humans is encoded by the NGLY1 gene. PNGase is a de-N-glycosylating enzyme that removes N-linked or asparagine-linked glycans (N-glycans) from glycoproteins. More specifically, NGLY1 catalyzes the hydrolysis of the amide bond between the innermost N-acetylglucosamine (GlcNAc) and an Asn residue on an N-glycoprotein, generating a de-N-glycosylated protein, in which the N-glycoylated Asn residue is converted to asp, and a 1-amino-GlcNAc-containing free oligosaccharide. Ammonia is then spontaneously released from the 1-amino GlcNAc at physiological pH (<8), giving rise to a free oligosaccharide with an N,N’-diacetylchitobiose structure at the reducing end.
Pycnodysostosis is a lysosomal storage disease of the bone caused by a mutation in the gene that codes the enzyme cathepsin K. It is also known as PKND and PYCD.
The AST/ALT ratio or De Ritis ratio is the ratio between the concentrations of two enzymes, aspartate transaminase (AST) and alanine transaminase, aka alanine aminotransferase (ALT), in the blood of a human or animal. It is used as one of several liver function tests, and measured with a blood test. It is sometimes useful in medical diagnosis for elevated transaminases to differentiate between causes of liver damage, or hepatotoxicity.
Aminolevulinic acid dehydratase deficiency porphyria is an extremely rare autosomal recessive metabolic disorder that results from inappropriately low levels of the enzyme delta-aminolevulinic acid dehydratase (ALAD), which is required for normal heme synthesis. This deficiency results in the accumulation of a toxic metabolic precursor in the heme synthesis pathway called aminolevulinic acid (ALA). Lead poisoning can also disrupt ALAD and result in elevated ALA causing the same symptoms. Heme is a component of hemoglobin which carries oxygen in red blood cells.
Alacrima refers to an abnormality in tear production that could mean reduced tear production or absent tear production. Because a lack of tears presents in only in a few rare disorders, it aids in diagnosis of these disorders, including Triple-A syndrome and NGLY1 deficiency.
Congenital hypofibrinogenemia is a rare disorder in which one of the three genes responsible for producing fibrinogen, a critical blood clotting factor, is unable to make a functional fibrinogen glycoprotein because of an inherited mutation. In consequence, liver cells, the normal site of fibrinogen production, make small amounts of this critical coagulation protein, blood levels of fibrinogen are low, and individuals with the disorder may develop a coagulopathy, i.e. a diathesis or propensity to experience episodes of abnormal bleeding. However, individuals with congenital hypofibrinogenemia may also have episodes of abnormal blood clot formation, i.e. thrombosis. This seemingly paradoxical propensity to develop thrombosis in a disorder causing a decrease in a critical protein for blood clotting may be due to the function of fibrin to promote the lysis or disintegration of blood clots. Lower levels of fibrin may reduce the lysis of early fibrin strand depositions and thereby allow these depositions to develop into clots.
Arginine:glycine amidinotransferase deficiency or AGAT deficiency is an autosomal recessive cerebral creatine deficiency caused by a deficiency of the enzyme arginine:glycine amidinotransferase. This enzyme deficiency results in decreased creatine synthesis, and is caused by biallelic pathogenic variants in GATM. Individuals with AGAT deficiency are intellectually disabled and have muscle weakness. The symptoms of AGAT deficiency are caused by the lack of creatine in specific tissues, most notably muscle and brain. Oral creatine supplementation can be used to treat AGAT deficiency, with early intervention providing the best results. All creatine deficiencies are rare, and there have been fewer than 20 individuals reported in medical literature with AGAT deficiency. This disorder was first described in 2000.
MPI-CDG is an autosomal recessive congenital disorder of glycosylation caused by biallelic pathogenic variants in MPI. The clinical symptoms in MPI-CDG are caused by deficient activity of the enzyme mannose phosphate isomerase. Clinically, the most common symptoms of MPI-CDG are chronic diarrhea, failure to thrive, protein-losing enteropathy, and coagulopathy. MPI-CDG differs from most other described glycosylation disorders due to its lack of central nervous system involvement, and because it has treatment options besides supportive care. Treatment with oral mannose has been shown to improve most symptoms of the disease. If left untreated, MPI-CDG can be fatal. MPI-CDG was previously known as CDG-IB. The disorder was first described clinically in 1986, and the underlying genetic defect was identified in 1998.
Dopamine transporter deficiency syndrome (DTDS), also known as infantile parkinsonism-dystonia, is a rare movement disorder that causes progressively worsening dystonia and parkinsonism. It is the first known inherited dopamine 'transportophathy.'
Mitochondrial complex II deficiency, also called CII deficiency, is a rare mitochondrial disease caused by deficiency of mitochondrial complex II, also known as Succinate dehydrogenase (SDH). SDH plays a key role in metabolism; the catalytic end, made up of SDHA and SDHB oxidizes succinate to fumarate in the tricarboxylic acid (TCA) cycle. The electrons from this reaction then reduce FAD to FADH2, which ultimately reduces ubiquinone to ubiquinol in the mitochondrial electron transport chain. As of 2020, about 61 cases have been reported with genetic studies, but there are also documented cases of CII deficiencies as determined by biochemical and histological analysis without genetic studies.
