Mitotic errors during early embryonal cell cleavage result in somatic cells having different genotypes. Such somatic mosaicism, in the presence of a chromosomal or genetic disorder, generally results in a milder disease phenotype, which may go undetected. We describe a case of mosaic tuberous sclerosis (TS) and the circumstances leading to its diagnosis. A 39-year-old man was referred to the adult neurology services for episodes of facial flushing, lip smacking, gustatory hallucinations and clenching movements of his left hand. EEG captured a complex partial seizure with correlating rhythmic θ activity over the right fronto-temporal area. MRI brain in 2004 showed a single high signal area in the right temporal lobe that was deemed artefactual. He was started on levetiracetam and later carbamazepine and was added, with good control. In 2009, his twin children were both diagnosed with tuberous sclerosis caused by a TSC2 exon 9 deletion. Neither the patient nor his wife carried the deletion in blood DNA. To investigate the possibility of somatic mosaicism, both parents underwent renal ultrasound. The patient's ultrasound revealed multiple hyperechoic foci throughout both kidneys typical in appearance of angiomyolipomas. Repeat MRI in 2010 showed disseminated lesions in both hemispheres, suggestive of cortical dysplasia that had emerged in the intervening 6 years. He was diagnosed with mosaic TS, and continues to be regularly reviewed for his epilepsy and renal lesions.
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