Methylmalonic Acidemia with Homocystinuria, Type cblD

What is methylmalonic acidemia with homocystinuria, type cblD?

Methylmalonic acidemia with homocystinuria, type cblD is an inherited condition in which the body is unable to metabolize certain proteins and fats properly. This leads to a buildup of a toxic level of methylmalonic acid in the blood. It is one of several conditions called an “inborn error of metabolism.” To understand this condition, it helps to know how certain amino acids are broken down:

• Each amino acid has its own pathway using a series of enzymes
• Each enzyme is essential to convert one substance to another
• If an enzyme is faulty, it results in the buildup of harmful products before the block, much in the same way that traffic builds up when there’s an accident on a busy road.

Thus, if you have an organic aciduria, an important class of inherited metabolic disorders, one of the enzymes is not functioning properly. The organic acids that build up before the block in the pathway give the name to each condition; a buildup of methylmalonic acid, for example, is called methylmalonic aciduria.

What are the signs and symptoms associated with methylmalonic acidemia with homocystinuria, type cblD?

Signs and symptoms vary from individual to individual, and may present at different ages. They generally develop in the first few months of life, and may include:

• Failure to thrive
• Lethargy
• Vomiting
• Dehydration
• Hypotonia (decreased muscle tone)
• Developmental delay
• Seizures
• Ataxia (problems with muscle control)
• Feeding difficulties
• Enlarged liver (hepatomegaly)

What treatment options are available for methylmalonic acidemia with homocystinuria, type cblD?

Although there isn’t a cure for this condition, treatments focus on alleviating some of the associated symptoms and may include various medications and/or supplements. The main aim of treatment is to keep the level of harmful acids in the blood down at safe levels. People diagnosed with an organic aciduria often have their dietary protein restricted or are advised to be cautious of the amount of protein they eat. Restriction of protein is important as it reduces the buildup of harmful organic acids. A dietitian can teach you how to measure protein-containing foods and control the amount of protein in your diet. All other foods can be eaten freely and will not need measuring/weighing. In addition to diet, some medications can also be used; the most common are listed below:

• Carnitine: helps mop up the toxic organic acid from the blood, allowing it to be cleared in the urine
• Glycine: works in the same way as carnitine. In some conditions, it can be given as a stand-alone therapy
• Metronidazole: an antibiotic given in a very low dose (rather than a dose required to fight infection). Normal bacteria that live in the gut make organic acids. Metronidazole is used to reduce the amount of gut bacteria and decrease the amount of organic acid made and absorbed from the gut

 

Where can I find more information about methylmalonic acidemia with homocystinuria, type cblD?

• E-IMD
• Genetic and Rare Disease Information Center
• Medline Plus
• Orphanet