A lack of this enzyme disrupts the normal balance of fatty acid formation and breakdown. As a result, fatty acids cannot be converted to energy, which can lead to characteristic features of this disorder, such as low blood sugar and cardiomyopathy. By-products of fatty acid processing build up in tissues, which also contributes to the signs and symptoms of malonyl-CoA decarboxylase deficiency. Malonyl-CoA decarboxylase deficiency is inherited in an autosomal recessive pattern. This means that the defective gene is located on an autosome (chromosome 16 is an autosome), and two copies of the defective gene - one inherited from each parent - are required to be born with the disorder. The parents of a child with an autosomal recessive disorder both carry one copy of the defective gene, but are usually not affected by the disorder. Malonyl-CoA decarboxylase deficiency is extremely rare, evidence suggests that it is caused by the abnormality in the protein transcription regulation. Looking at the molecular basis, two distinct homozygous mutations are found to cause Malonyl-CoA  Decarboxylase deficiency in human. The first mutation is the transversion of gene from C to G causing a premature stop signal in the protein. The second mutation is a base pair insertion in the mature RNA that will eventually result in the protein truncation.A research has also confirmed that the homozygous mutation which eventually leads to MCD deficiency is caused by the isodisomy of maternal UPD. This indicates that such disease is likely to be inherited from mother’s gene profile, not from paternal source.
Diagnosis
Differential diagnoses
The differential diagnosis includes elastofibroma, fibrolipoma, desmoid-type fibromatoses, and nuchal fibrocartilaginous pseudotumor. Management
Simple excision is curative. However, in patients with Gardner syndrome, up to 45% will develop desmoid-type fibromatosis at other sites, and so this should be searched for and excluded. Patients can develop a recurrence, so follow-up is required. Epidemiology
This is a rare tumor, presenting over a wide age range, but usually in the 3rd to 5th decades of life. There is a slight male predilection, although this is not seen in syndrome associated patients. The most common site is the posterior neck, but may also be seen in other sites (extremities, lumbosacral area, buttocks, face). See also
Fibrous Lesions

References
Further reading
Lester D. R. Thompson; Bruce M. Wenig (2011). Diagnostic Pathology: Head and Neck: Published by Amirsys. Hagerstown, MD: Lippincott Williams & Wilkins. pp. 8:44–45. ISBN 978-1-931884-61-7.