Question: What are the genetic changes related to methylmalonic acidemia with homocystinuria ?
Answer: Methylmalonic acidemia with homocystinuria can be caused by mutations in one of several genes: MMACHC, MMADHC, LMBRD1, ABCD4, or HCFC1. Mutations in these genes account for the different types of the disorder, which are known as complementation groups: cblC, cblD, cblF, cblJ, and cblX, respectively. Each of the above-mentioned genes is involved in the processing of vitamin B12, also known as cobalamin or Cbl. Processing of the vitamin converts it to one of two molecules, adenosylcobalamin (AdoCbl) or methylcobalamin (MeCbl). AdoCbl is required for the normal function of an enzyme that helps break down certain amino acids, lipids, and cholesterol. AdoCbl is called a cofactor because it helps the enzyme carry out its function. MeCbl is also a cofactor, but for another enzyme that converts the amino acid homocysteine to another amino acid, methionine. The body uses methionine to make proteins and other important compounds. Mutations in the MMACHC, MMADHC, LMBRD1, ABCD4, or HCFC1 gene affect early steps of vitamin B12 processing, resulting in a shortage of both AdoCbl and MeCbl. Without AdoCbl, proteins and lipids are not broken down properly. This defect allows potentially toxic compounds to build up in the body's organs and tissues, causing methylmalonic acidemia. Without MeCbl, homocysteine is not converted to methionine. As a result, homocysteine builds up in the bloodstream and methionine is depleted. Some of the excess homocysteine is excreted in urine (homocystinuria). Researchers have not determined how altered levels of homocysteine and methionine lead to the health problems associated with homocystinuria. Mutations in other genes involved in vitamin B12 processing can cause related conditions. Those mutations that impair only AdoCbl production lead to methylmalonic acidemia, and those that impair only MeCbl production cause homocystinuria.
Source: GHR

Question: What are the treatments for methylmalonic acidemia with homocystinuria ?
Answer: These resources address the diagnosis or management of methylmalonic acidemia with homocystinuria: - Baby's First Test: Methylmalonic Acidemia with Homocystinuria - Gene Review: Gene Review: Disorders of Intracellular Cobalamin Metabolism - Genetic Testing Registry: METHYLMALONIC ACIDURIA AND HOMOCYSTINURIA, cblF TYPE - Genetic Testing Registry: METHYLMALONIC ACIDURIA AND HOMOCYSTINURIA, cblJ TYPE - Genetic Testing Registry: Methylmalonic acidemia with homocystinuria - Genetic Testing Registry: Methylmalonic acidemia with homocystinuria cblD These resources from MedlinePlus offer information about the diagnosis and management of various health conditions: - Diagnostic Tests - Drug Therapy - Surgery and Rehabilitation - Genetic Counseling - Palliative Care
Source: GHR