ABC of Gaze and Ocular Oscillations.

The chief goal of all eye movements is to maintain the image of an object steady on the retina especially the macula to preserve visual acuity. Gaze palsy refers to lack of the conjugate movements due to a failure of supranuclear control mechanisms. Supranuclear control is maintained by not one, but multiple eye movement systems and gaze mechanisms. Supranuclear gaze palsies can be associated with a myriad of aetiologies- from trauma or metabolic abnormalities to stroke, demyelinating disorders and space occupying lesions like tumours. Culprit lesions may be in frontal motor centres, brainstem gaze centres gaze or interconnecting segments. While the brainstem network for horizontal gaze lies in pons, that for vertical gaze is situated in midbrain. Further, ocular oscillations and nystagmus are abnormal eye movements that disrupt a steady fixation of gaze. It is prudent to be aware of various gaze pathways and their anatomical corelates in order to establish a topographic relationship of clinical findings. A systematic clinical examination may provide deep insights on the patho-physiological mechanisms along with aiding in localizing the lesion accurately. This review deals with systematic clinical approach to various gaze control systems.

Mutation in glycerol-3-phosphate dehydrogenase 1 like gene (GPD1-L) decreases cardiac Na+ current and causes inherited arrhythmias.

BACKGROUND: Brugada syndrome is a rare, autosomal-dominant, male-predominant form of idiopathic ventricular fibrillation characterized by a right bundle-branch block and ST elevation in the right precordial leads of the surface ECG. Mutations in the cardiac Na+ channel SCN5A on chromosome 3p21 cause approximately 20% of the cases of Brugada syndrome; most mutations decrease inward Na+ current, some by preventing trafficking of the channels to the surface membrane. We previously used positional cloning to identify a new locus on chromosome 3p24 in a large family with Brugada syndrome and excluded SCN5A as a candidate gene. METHODS AND RESULTS: We used direct sequencing to identify a mutation (A280V) in a conserved amino acid of the glycerol-3-phosphate dehydrogenase 1-like (GPD1-L) gene. The mutation was present in all affected individuals and absent in >500 control subjects. GPD1-L RNA and protein are abundant in the heart. Compared with wild-type GPD1-L, coexpression of A280V GPD1-L with SCN5A in HEK cells reduced inward Na+ currents by approximately 50% (P<0.005). Wild-type GPD1-L localized near the cell surface to a greater extent than A280V GPD1-L. Coexpression of A280V GPD1-L with SCN5A reduced SCN5A cell surface expression by 31+/-5% (P=0.01). CONCLUSIONS: GPD1-L is a novel gene that may affect trafficking of the cardiac Na+ channel to the cell surface. A GPD1-L mutation decreases SCN5A surface membrane expression, reduces inward Na+ current, and causes Brugada syndrome.

Clinical and etiological profile of tropical ataxic neuropathy in Kerala, South India.

BACKGROUND/AIMS: Very little is known about the occurrence of tropical ataxic neuropathy (TAN) from southern India. This study describes the clinical spectrum of TAN from Kerala, southern India, and explores its etiology. METHODS: We reviewed the clinical and laboratory profile of 40 TAN cases diagnosed in a tertiary referral center in central Kerala. We enquired the consumption of cassava foods and estimated the thiocyanate levels in the serum, urine and sural nerve. RESULTS: The notable demographic characteristics included female preponderance, peak age at onset in the thirties, rural residence and poor socioeconomic status. The diet in the majority comprised a large amount of tapioca, which is low in protein. In addition to sensory peripheral neuropathy, 90% had decreased hearing, 50% had decreased vision, and 25% had spasticity involving the lower extremities. None had signs of overt vitamin deficiencies or malabsorption syndrome. Compared to the controls, the serum, urine and sural nerve thiocyanate levels were significantly elevated in the patients. With cessation of cassava intake and better nutrition, improvement in the neurological disability occurred in the majority. CONCLUSIONS: This study, for the first time, provides evidence for the occurrence of TAN in south India and the possible etiological role of cassava intake.