Bilateral external ophthalmoplegia in biotin-responsive basal ganglia disease

Eye motor manifestations in children with neurometabolic disorders

Neurometabolic diseases are complex group of rare neurogenetic disorders, which are difficult to diagnose. Patients may have toxic metabolite accumulation, inadequate energy supply, or neurotransmitter deficiency, resulting in a variety of clinical manifestations and severity with enzyme activity or transporter function defects. Multiple organ involvement is frequently seen, among which neurological symptoms and signs are one of the most encountered problems. Ocular motor problems deserve special attention for it occurs in some inborn error of metabolism. Furthermore, some are early signs or characteristic findings of certain diseases, such as the gaze palsy in Niemann-Pick disease type C and Gaucher disease or oculogyric crisis in neurotransmitter diseases. Early recognition and intervention are important for better prognosis in treatable neurometabolic disorders. In addition, ways to evaluate and describe eye movement problems also help to demonstrate the severity or clinical progression for those diagnosed with certain neurometabolic diseases. However, the complexity of eye movement and ocular motor control renders our clinical observation, recording and even anatomic localization of abnormal eye movements. Clinicians are more likely to detect early signs and unravel problems by gaining awareness of abnormal eye movement. This study amied to approach neurometabolic diseases in children via eye motor manifestations.

Report of the Largest Chinese Cohort With SLC19A3 Gene Defect and Literature Review

Thiamine metabolism dysfunction syndrome 2 (THMD2) is a rare metabolic disorder caused by SLC19A3 mutations, inherited in autosomal recessive pattern. As a treatable disease, early diagnosis and therapy with vitamin supplementation is important to improve the prognosis. So far, the reported cases were mainly from Saudi Arab regions, and presented with relatively simple clinical course because of the hot spot mutation (T422A). Rare Chinese cases were described until now. In this study, we investigated 18 Chinese THMD2 patients with variable phenotypes, and identified 23 novel SLC19A3 mutations, which expanded the genetic and clinical spectrum of the disorder. Meanwhile, we reviewed all 146 reported patients from different countries. Approximately 2/3 of patients presented with classical BTBGD, while 1/3 of patients manifested as much earlier onset and poor prognosis, including infantile Leigh-like syndrome, infantile spasms, neonatal lactic acidosis and infantile BTBGD. Literature review showed that elevated lactate in blood and CSF, as well as abnormal OXPHOS activities of muscle or skin usually correlated with infantile phenotypes, which indicated poor outcome. Brainstem involvement on MRI was more common in deceased cases. Thiamine supplementation is indispensable in the treatment of THMD2, whereas combination of biotin and thiamine is not superior to thiamine alone. But biotin supplementation does work in some patients. Genotypic-phenotypic correlation remains unclear which needs further investigation, and biallelic truncated mutations usually led to more severe phenotype.

Eye movement disorders and neurological symptoms in late-onset inborn errors of metabolism

Inborn errors of metabolism in adults are still largely unexplored. Despite the fact that adult‐onset phenotypes have been known for many years, little attention is given to these disorders in neurological practice. The adult‐onset presentation differs from childhood‐onset phenotypes, often leading to considerable diagnostic delay. The identification of these patients at the earliest stage of disease is important, given that early treatment may prevent or lessen further brain damage. Neurological and psychiatric symptoms occur more frequently in adult forms. Abnormalities of eye movements are also common and can be the presenting sign. Eye movement disorders can be classified as central or peripheral. Central forms are frequently observed in lysosomal storage disorders, whereas peripheral forms are a key feature of mitochondrial disease. Furthermore, oculogyric crisis is an important feature in disorders affecting dopamine syntheses or transport. Ocular motor disorders are often not reported by the patient, and abnormalities can be easily overlooked in a general examination. In adults with unexplained psychiatric and neurological symptoms, a special focus on examination of eye movements can serve as a relatively simple clinical tool to detect a metabolic disorder. Eye movements can be easily quantified and analyzed with video‐oculography, making them a valuable biomarker for following the natural course of disease or the response to therapies. Here, we review, for the first time, eye movement disorders that can occur in inborn errors of metabolism, with a focus on late‐onset forms. We provide a step‐by‐step overview that will help clinicians to examine and interpret eye movement disorders. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.