Congenital ocular motor apraxia associated with idiopathic generalized epilepsy in monozygotic twins

Identical female twins (age 11 years) with congenital ocular motor apraxia and generalized idiopathic epilepsy are reported. Their presenting symptoms were a long history of abnormal head and eye movements. One twin developed partial sensory seizures. The patients underwent 16-channel EEG, electro-oculographic recordings, MRI of the brain, and genetic and metabolic investigations. EEG findings were consistent with idiopathic generalized epilepsy. Electrooculographic recordings of the saccades confirmed an inability to elicit horizontal saccades without preceding head movement; saccades to the left were better than saccades to the right. MR scans for one twin showed normal findings, however, for the twin who had meningitis they revealed asymmetry between the right and left temporal lobes but no specific abnormality. DNA analysis using a series of autosomal polymorphic markers confirmed the monozygocity of the twins. White blood cell enzyme analysis excluded Sandhoff disease, Tay-Sachs disease, GM1 gangliosidosis, metacromatic leucodystrophy, Gaucher disease, Niemann-Pick disease (A and B), and Krabbe leucodystrophy. Albumin and immunoglobulin (IgA, IgG, and IgM) levels were normal. It is concluded that autosomal recessive inheritance seems the most likely explanation here, as recent studies have found insertion and missense mutations of the aprataxin gene which have been related to an early onset form of ataxia with ocular motor apraxia and hypoalbuminaemia.