Description
Molybdenum cofactor deficiency is a rare condition characterized by brain dysfunction (encephalopathy) that worsens over time. Babies with this condition appear normal at birth, but within a week they have difficulty feeding and develop seizures that do not improve with treatment (intractable seizures). Brain abnormalities, including deterioration (atrophy) of brain tissue, lead to severe developmental delay; affected individuals usually do not learn to sit unassisted or to speak. A small percentage of affected individuals have an exaggerated startle reaction (hyperekplexia) to unexpected stimuli such as loud noises. Other features of molybdenum cofactor deficiency can include a small head size (microcephaly) and facial features that are described as "coarse."
Tests reveal that affected individuals have high levels of chemicals called sulfite, S-sulfocysteine, xanthine, and hypoxanthine in the urine and low levels of a chemical called uric acid in the blood.
Because of the serious health problems caused by molybdenum cofactor deficiency, affected individuals usually do not survive past early childhood.
Frequency
Molybdenum cofactor deficiency is a rare condition that is estimated to occur in 1 in 100,000 to 200,000 newborns worldwide. More than 100 cases have been reported in the medical literature, although it is thought that the condition is underdiagnosed, so the number of affected individuals may be higher.
Causes
Molybdenum cofactor deficiency is caused by mutations in the MOCS1, MOCS2, or GPHN gene. There are three forms of the disorder, named types A, B, and C (or complementation groups A, B, and C). The forms have the same signs and symptoms but are distinguished by their genetic cause: MOCS1 gene mutations cause type A, MOCS2 gene mutations cause type B, and GPHN gene mutations cause type C. The proteins produced from each of these genes are involved in the formation (biosynthesis) of a molecule called molybdenum cofactor. Molybdenum cofactor, which contains the element molybdenum, is essential to the function of several enzymes. These enzymes help break down (metabolize) different substances in the body, some of which are toxic if not metabolized.
Mutations in the MOCS1, MOCS2, or GPHN gene reduce or eliminate the function of the associated protein, which impairs molybdenum cofactor biosynthesis. Without the cofactor, the metabolic enzymes that rely on it cannot function.
The resulting loss of enzyme activity leads to buildup of certain chemicals, including sulfite, S-sulfocysteine, xanthine, and hypoxanthine (which can be identified in urine), and low levels of uric acid in the blood. Sulfite, which is normally broken down by one of the molybdenum cofactor-dependent enzymes, is toxic, especially to the brain. Researchers suggest that damage caused by the abnormally high levels of sulfite (and possibly other chemicals) leads to encephalopathy, seizures, and the other features of molybdenum cofactor deficiency.
Inheritance
Molybdenum cofactor deficiency has an autosomal recessive pattern of inheritance, which means both copies of the gene in each cell have mutations. An affected individual usually inherits one altered copy of the gene from each parent. Parents of an individual with an autosomal recessive condition typically do not show signs and symptoms of the condition.
At least one individual with molybdenum cofactor deficiency inherited two mutated copies of the MOCS1 gene through a mechanism called uniparental isodisomy. In this case, an error occurred during the formation of egg or sperm cells, and the child received two copies of the mutated gene from one parent instead of one copy from each parent.
Other Names for This Condition
- Combined deficiency of sulfite oxidase, xanthine dehydrogenase, and aldehyde oxidase
- Combined molybdoflavoprotein enzyme deficiency
- Combined xanthine oxidase and sulfite oxidase and aldehyde oxidase deficiency
- Deficiency of molybdenum cofactor
- MOCOD
Additional Information & Resources
Genetic Testing Information
- Genetic Testing Registry: Combined molybdoflavoprotein enzyme deficiency
- Genetic Testing Registry: Sulfite oxidase deficiency due to molybdenum cofactor deficiency type A
- Genetic Testing Registry: Sulfite oxidase deficiency due to molybdenum cofactor deficiency type B
- Genetic Testing Registry: Sulfite oxidase deficiency due to molybdenum cofactor deficiency type C
Genetic and Rare Diseases Information Center
Patient Support and Advocacy Resources
Clinical Trials
Scientific Articles on PubMed
References
- Bayram E, Topcu Y, Karakaya P, Yis U, Cakmakci H, Ichida K, Kurul SH. Molybdenum cofactor deficiency: review of 12 cases (MoCD and review). Eur J Paediatr Neurol. 2013 Jan;17(1):1-6. doi: 10.1016/j.ejpn.2012.10.003. Epub 2012 Oct 31. Citation on PubMed
- Mendel RR. The molybdenum cofactor. J Biol Chem. 2013 May 10;288(19):13165-72. doi: 10.1074/jbc.R113.455311. Epub 2013 Mar 28. Citation on PubMed or Free article on PubMed Central
- Reiss J, Gross-Hardt S, Christensen E, Schmidt P, Mendel RR, Schwarz G. A mutation in the gene for the neurotransmitter receptor-clustering protein gephyrin causes a novel form of molybdenum cofactor deficiency. Am J Hum Genet. 2001 Jan;68(1):208-13. doi: 10.1086/316941. Epub 2000 Nov 28. Citation on PubMed or Free article on PubMed Central
- Reiss J, Johnson JL. Mutations in the molybdenum cofactor biosynthetic genes MOCS1, MOCS2, and GEPH. Hum Mutat. 2003 Jun;21(6):569-76. doi: 10.1002/humu.10223. Citation on PubMed
- Veldman A, Santamaria-Araujo JA, Sollazzo S, Pitt J, Gianello R, Yaplito-Lee J, Wong F, Ramsden CA, Reiss J, Cook I, Fairweather J, Schwarz G. Successful treatment of molybdenum cofactor deficiency type A with cPMP. Pediatrics. 2010 May;125(5):e1249-54. doi: 10.1542/peds.2009-2192. Epub 2010 Apr 12. Citation on PubMed
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