P627 Mitochondrial disease mimics

A diagnosis of primary mitochondrial disease was traditionally arrived at on the basis of clinical and biochemical features including abnormal respiratory chain analysis on muscle biopsy and/or identification of other ‘mitochondrial disease markers’. With the increased availability of genetic testing, in particular massive parallel sequencing, alternative primary diagnoses which result in secondary mitochondrial dysfunction are being identified We present a cohort of six cases who previously had a diagnosis of mitochondrial disease. Alternative primary diagnoses have recently been identified which includes Andersen-Tawil syndrome (gene: KCNJ2), COL4A1-related brain small-vessel disease (gene: COL4A1), cardiofaciocutaneous syndrome (gene: BRAF), autosomal recessive spinal cerebellar ataxia-10 (gene: ANO10), facioscapulohumeral muscular dystrophy (gene: DUX4) and IGSF1 deficiency syndrome (gene: IGSF1). Conclusion The reported cohort highlights the important point that many genetic conditions may mimic mitochondrial disease and, although the phenotype and biochemical tests may indicate mitochondrial disease, we suggest that genetic confirmation is required to secure a diagnosis. Establishment of an accurate diagnosis is important, not just prognosis and planning of management and treatments regimes, but also for appropriate genetic counseling and the identification of other at-risk family members for possible cascade analysis. The link between many of these primary diagnoses and secondary mitochondrial dysfunction is poorly understood but reporting such cases will allow these pathways to be elucidated and understood.