Genomic analysis of patients in a South Indian Community with autosomal dominant cortical tremor, myoclonus and epilepsy suggests a founder repeat expansion mutation in the SAMD12 gene.

Autosomal Dominant Cortical Tremor, Myoclonus and Epilepsy is a non-progressive disorder characterized by distal tremors. Autosomal Dominant Cortical Tremor, Myoclonus and Epilepsy has been reported globally with different genetic predispositions of autosomal dominant inheritance with a high degree of penetrance. In south India, Autosomal Dominant Cortical Tremor, Myoclonus and Epilepsy has been reported in a large cohort of 48 families, in which the genetic defect was not identified. This report pertains to the whole-genome analysis of four individuals followed by repeat-primed PCR for 102 patients from a familial cohort of 325 individuals. All the patients underwent extensive clinical evaluation including neuropsychological examinations. The whole-genome sequencing was done for two affected and two unaffected individuals, belonging to two different families. The whole-genome sequencing analysis revealed the repeat expansion of TTTTA and TTTCA in intron 4 of the SAMD12 gene located on chromosome 8 in the patients affected with Autosomal Dominant Cortical Tremor, Myoclonus and Epilepsy, whereas the unaffected family members were negative for the similar expansion. Further, the repeat-primed PCR analysis of 102 patients showed the expansion of the TTTCA repeats in the intron 4 of SAMD12 gene. All patients registered for this study belong to a single community called "Nadar" whose nativity is confined to the southern districts of India, with reported unique genetic characteristics. This is the largest and most comprehensive single report on clinically and genetically characterized Autosomal Dominant Cortical Tremor, Myoclonus and Epilepsy patients belonging to a unique ethnic group worldwide.

Autosomal dominant cortical tremor, myoclonus, and epilepsy (ADCME) in a unique south Indian community.

Autosomal dominant cortical tremor, myoclonus, and epilepsy (ADCME)/familial adult onset myoclonic epilepsy (FAME) is a nonprogressive disorder characterized by (1) distal tremors that are usually precipitated by posture and action; (2) stimulus-sensitive myoclonus that is predominantly seen in the upper limb and is precipitated by photic stimuli, fatigue, emotional stress, and sleep deprivation; (3) seizures that were predominantly of the generalized tonic-clonic type that showed significant response to antiepileptic drugs (AEDs). ADCME has been reported worldwide with different genetic loci in Japanese families (8q23.3-q24.1), Italian families (2p11.1-q12.2), a French family (5p15.3.1-p15.1), and a Thai family (3q26.32-q28). ADCME has not been reported in South India and is still not recognized as an independent entity under the International League Against Epilepsy (ILAE). We report 241 patients with ADCME identified belonging to 48 families. The 48 families are domiciled in two southern districts of Tamilnadu in India, belonging to a community called "Nadar" whose nativity is confined to these southern districts, with reported unique genetic characteristics. This study is reported for the presentation of this rare disease in a unique ethnic group, and is the largest single report on ADCME worldwide.