Trisomy 12p syndrome: a chromosomal disorder associated with generalized 3-Hz spike and wave discharges.

Three cases (2 boys, 1 girl) of trisomy 12p syndrome are reported. In two, the disorder is caused by a malsegregation of a maternal translocation, the karyotype being 46,XY,der(18),t(12;18)(p11;q23) (case 2) and 46,XX,-10,+ der(10),t(10;12)(p15;p11) (case 3). Case 1 is a de novo case with a regular trisomy 12p in the fibroblasts: 47,XY + (12pter----12 cen. . .?) and a mosaic trisomy 12p in lymphocytes: 46,XY/47,XY, + (12pter----12 cen. . .?). In all cases, the EEG showed 3-Hz generalized spike and wave (SW) discharges. Generalized epilepsy with myoclonic seizures was present in two patients (cases 1 and 2), who may be considered to have a symptomatic generalized epilepsy with a specific etiology. Case 3 has shown only febrile seizures. Any association between the excess of genetic material and the EEG trait "generalized SW" might not be a chance occurrence in this disorder; however, both EEG findings and clinical features (seizure type and frequency) in the 23 cases reported in the literature are too scanty to allow confirmation of such an association.