BACKGROUND:Psychiatric syndromes have polymorphic symptomatology, and are known to be heritable. Psychiatric symptoms (and even syndromes) often occur as part of the clinical presentation in rare Mendelian syndromes. Clinical exome sequencing reports may help with refining diagnosis and influence treatment decisions, in addition to providing a window into the biology of brain and behaviour. We describe a clinical audit of 12 individuals who sought treatment at our hospital, and for whom targeted sequencing was ordered. Three cases are discussed in detail to demonstrate correlations between genotype and phenotype in the clinic.METHODS:Targeted Next-Generation Sequencing (NGS) was done using Clinical Exome Panel (TruSight One, Illumina) covering coding exons and flanking intronic sequences of 4811 genes associated with known inherited diseases. Variants detected were classified according to the American College for Medical Genetics (ACMG) recommendation for standards of interpretation and reporting of sequence variations.RESULTS:Ten out of twelve cases had at least one pathogenic variant. In one of these cases, we detected a known pathogenic variant in MAPT gene in a suspected FTD case, which helped us to confirm the diagnosis. In another case, we detected a novel variant predicted to be deleterious in NF1 gene. Identification of this mutation suggested a change in treatment for the patient, that was of benefit. The same patient also harboured a novel variant in the TRIO gene. This gene may be involved in biological processes that underlie the patient’s psychiatric illness.CONCLUSIONS:The cases discussed here exemplify different scenarios under which targeted exome sequencing can find meaningful application in the clinic: confirming diagnosis (MAPT variant), or modifying treatment (NF1). We suggest that clinical exome sequencing can be a helpful addition to a clinician’s toolkit when there are expediting factors to consider— such as early-onset, strong family history of mental illness, complex/atypical presentations and minor physical anomalies or neurocutaneous markers.