Molecular Genetic Testing

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The mitochondrial mutation m.3243A>G is associated with the MELAS syndrome (mitochondrial encephalopathy, lactic acidosis, stroke-like episodes; Goto et al 1990 Nature 348, 651-653) and the MIDD syndrome (maternally inherited diabetes and deafness; Ballinger et al 1992 Nat Genet 1, 11-15).  Additional clinical features associated with the m.3243A>G mutation include short stature, cardiomyopathy, myopathy, renal disease, macular dystrophy and gastrointestinal disease (Murphy et al 2008 Diabet Med 25, 383-399).  Mitochondrial mutations are passed on through the maternal germline, and so all maternal relatives of an individual with MIDD or MELAS are likely to be obligate carriers of the m.3243A>G mutation.  However the clinical phenotype associated with the m.3243A>G mutation may be very heterogeneous, even within the same family (Nesbitt et al 2013 J Neurol Neurosurg Psychiatry 84, 936-938).  Part of this variation in phenotype is as a result of the amount of heteroplasmy (the mixture of wild-type and mutant mitochondrial DNA in each cell) inherited, the subsequent segregation of mutant mitochondrial DNA in the different tissues and changes in the level of heteroplasmy in different tissues with increasing age.

Samples for testing


Collect the first 20ml of an early morning urine sample into a sterile universal container.  Send to the laboratory with a completed request form by first class post on the day the sample is taken.


The m.3243A>G mutation can be detected in virtually all tissues; however heteroplasmy differs between sample types.

Blood leukocytes generally contain the lowest level of the m.3243A>G mutation.  Therefore it is possible to obtain a negative result for m.3243A>G in blood, despite the presence of the mutation in other tissues. Of the readily accessible tissues available for testing, urine epithelial cells contain the highest level of the m.3243A>G mutation and urine is therefore the preferred sample to test (de Laat et al 2012 J Inherit Metab Dis 35, 1059-1069


m.3243A>G analysis by Real-Time PCR



Download MODY request form



Link to patient information sheet




The laboratory participates in the United Kingdom National External Quality Assessment Service (UK NEQAS) Mitochondrial Diseases scheme.