Formerly Professor of Developmental Psychiatry at the University of Edinburgh and Honorary Consultant Psychiatrist (Learning Disability), NHS Lothian

Walter was born on 13 February 1958 in Edinburgh, the city where he spent his working career. He qualified MBChB from the University of Edinburgh in 1983 after completing an intercalated degree in pharmacology, graduating with first-class honours in 1980. This undergraduate laboratory-based experience was the start of a lifelong interest in neuroscience and the biological basis of behaviour. After house officer posts in the Royal Infirmary, he joined the Royal Edinburgh Hospital rotational training scheme in psychiatry in 1984 and took the opportunity offered by the Wellcome Trust research registrar scheme to combine clinical training with academic research. This was a time when molecular genetic approaches to complex disorders, including schizophrenia and bipolar disorder, were becoming attractive because of advances in DNA technology and the increasing availability of polymorphic DNA markers for mapping genes. Walter became involved in family genetic studies and, aware of the limitations in psychiatry of purely symptom-based diagnoses, he investigated the role of electrophysiological biomarkers. Families volunteering for genetic studies were often asked to take part in recordings of brain waves and eye movements, and Walter published several key papers describing disordered P300 auditory event-related potentials and eye movements in schizophrenia and bipolar disorder. He had a natural gift for designing and setting up electrophysiological studies which were also an opportunity for him to continue a long-standing interest in physics and electronics. Indeed, he had been awarded an amateur radio licence at the early age of 19 and always remained an active ‘radio ham’ whenever time permitted.

After qualifying MRCPsych in 1987, Walter continued genetic research as a member of the MRC Brain Metabolism Unit based at the Royal Edinburgh Hospital and was awarded a prestigious MRC Clinician Scientist Fellowship, which he held for 6 years before becoming a consultant. He recognised the potential value of naturally occurring chromosomal abnormalities as significant signposts to the location of illness-related genes in psychiatry. To further this approach, encouraged by the late Professor John Evans at the MRC Human Genetics Unit in Edinburgh, he worked with a large database of chromosomal abnormalities previously established in the MRC Unit, and from this he identified several key families where chromosomal abnormalities were the most likely cause of psychiatric illness. This was an immensely productive time for research, and his combination of clinical and laboratory skills, particularly a training in cytogenetics, underpinned the work that eventually led to the discovery of several genes contributing to risk of schizophrenia and bipolar disorder, including the gene DISC1, to date one of the most studied candidate genes for neuropsychiatric illness. Other important genes identified by Walter and his colleagues using a cytogenetic approach include GRIK4, NPAS3, PDE4B and ABCA13, implicating a variety of pathways in the pathology of psychoses. He authored over 160 published papers on gene-mapping studies and wrote several book chapters and reviews on the effects of psychiatric illness in individuals with intellectual disabilities.

It was natural when Walter was appointed senior lecturer at Edinburgh University's Department of Psychiatry and honorary consultant psychiatrist with NHS Lothian in 1995 that he chose to specialise in the psychiatry of learning disability, as he had a particular interest in the very disabled group of patients with intellectual disability and comorbid schizophrenia or bipolar disorder. He established a group of researchers within the specialty and made an important contribution to international multicentre collaborations, carrying out genome-wide association studies in schizophrenia, bipolar disorder and depression by including a group of patients with intellectual disabilities in these large-scale studies. He regularly reviewed research grants and papers for journals and was a member of the Biomedical and Therapeutic Research Committee of the Chief Scientist Office of the Scottish Government and specialty advisor on the psychiatry of learning disability to the Chief Medical Officer in Scotland.

However, genetic research was not his only interest and he worked long hours seeing patients, their families and carers. As training programme director he oversaw a doubling of specialty registrar posts in learning disability in the region and set up peer support and continuing professional development groups to raise standards of service provision. With a practical, down-to-earth approach to the management of complex clinical situations and the ability to make strong rapport with patients, he consistently supported and gained the affection of many families coping with the long-term effects of illness. He was a member of several advisory groups on the psychiatry of learning disability, including the Rowntree Foundation, the Royal College of Psychiatrists, the Scottish Consortium for Learning Disabilities and the National Training Advisory Committee for Specialty Registrars in Learning Disability. He maintained strong links with charities and was the medical advisor to Down's Syndrome Scotland for 15 years and a trustee of Autism Speaks UK.

His contributions are all the more remarkable as he lived with a progressive hearing impairment, about which he never complained, although he found it a severe handicap at meetings and speaking at conferences when it eventually became an insurmountable challenge. Despite deafness, he was a skilled pianist and collected many books on a vast range of subjects from radio to borders history. He was great company, and an inspiration to everyone.

His sudden death aged 51 on 1 September 2009, following an accident in Fife, was only a few months after he was awarded a DSc and appointed to a Personal Chair in Developmental Psychiatry in Edinburgh University. He was greatly looking forward to the next stage of applying the growing knowledge of genetic causes of psychiatric illness to improving the lives of his patients and their relatives. He leaves a son, Alisdair, and a daughter, Catherine, both at university.