Ocular Motor Apraxia

Description

Congenital oculomotor apraxia, first reported by Cogan (1952), is characterized by (1) defective or absent horizontal voluntary eye movements, and (2) defective or absent horizontal ocular attraction movements.

Oculomotor apraxia occurs in ataxia-telangiectasia (208900). Also see ataxia-oculomotor apraxia syndrome (208920; 606002). Oculomotor apraxia has been observed in the neuronopathic form of Gaucher disease (type III; 231000) (Erikson and Wahlberg, 1985; Gross-Tsur et al., 1989).

Clinical Features

Vassella et al. (1972) provided observations on 3 patients and summarized the findings on 33 previously reported cases in the literature. Random eye movements and voluntary vertical gaze are usually retained by the affected individuals. Compensation for the defective horizontal eye movements is accomplished through rotating the head sharply laterally to bring the eyes forcefully to view the desired object. The eyes tend to deviate in the opposite direction from this movement because of the vestibular reflex necessitating even a greater head swing. Thus, the most noticeable feature of the condition in young patients is jerking movements of the head. The disease is not progressive, and older patients may be able to compensate by an over-shooting thrust of the eyeballs rather than by head jerks. Twenty-three of 34 cases were male.

Orrison and Robertson (1979) reported a series that included a brother (aged 18 months) and his sister (aged 42 months). Development had been normal except that neither walked without support until age 15 months. The parents had noted that from infancy both turned their heads to look at objects at either side but the ability to look from side to side had improved somewhat. Horizontal opticokinetic nystagmus and apraxia of horizontal gaze were the only abnormalities. Both children used a thrusting motion of the head when looking to either side.

Narbona et al. (1980) described a sister (aged 4 years) and brother (aged 2.5 years) with oculomotor apraxia and selective IgA deficiency but no telangiectases. It is likely that this was ataxia-telangiectasia in its pre-telangiectasia stage.

Harris et al. (1998) suggested that congenital saccade initiation failure (c-SIF) is a more specific name for this disorder because it avoids the erroneous implications that the disorder is necessarily a high-level problem as the term 'apraxia' should indicate, and that saccades are necessarily slow as the term 'supranuclear gaze palsy' often implies. In a brother and sister with this disorder they found typical signs of c-SIF, including head thrusting, synkinetic blinking, missed-nystagmus quick phases, mild developmental delay, and speech difficulties. CT and MRI revealed cerebellar vermis hypoplasia in the brother, but appeared normal in the sister. These cases highlighted the wide variability in the association of vermis abnormalities with c-SIF, despite the inheritance and similar clinical manifestations. They showed that either (1) the vermis is causal in saccade triggering, but that c-SIF may result from very subtle damage that is beyond MRI resolution in some cases; or (2) a vermis abnormality per se is not causative but only a marker of another subtle abnormality, either structural or biochemical.

Inheritance

Cogan (1972) reviewed reported cases in sibs, including offspring of first cousins, and reported 5 additional families. In 1 family, identical twins were concordantly affected. In another family, the mother and 2 male sibs were affected. These findings, and the fact that the condition improves with age so that the parent may not be aware that he or she had the condition as a child, led Cogan (1972) to suggest that dominant inheritance cannot be rejected out of hand.

Robles (1966) reported identical twins with the condition. Sachs (1967) and Arthuis (1971) observed the disorder in sibs, with Sachs' case being of consanguineous parents.

Vassella et al. (1972) reported cases occurring in 2 generations; the father (affected) and mother were first cousins. Thus, this may be an instance of recessive inheritance with a pseudodominant pattern.

Mapping

Betz et al. (2000) identified 2 patients with Cogan-type congenital ocular motor apraxia (COMA) and associated nephronophthisis-1 (NPHP1; 256100). One patient had a deletion on each chromosome 2q13, and the other patient had a deletion on one 2q13 chromosome and a point mutation of the NPHP1 gene (607100.0004) in the other. The authors suggested that COMA may be a contiguous gene defect with NPHP1 and that it may be an autosomal dominant condition.