Professor Louis Woolf died aged 101 from a heart condition on Sunday February 7, 2021 in Vancouver, British Columbia. He is best known for his pioneering work developing his concept of a dietary treatment for phenylketonuria, PKU, based on a phenylalanine ‐ depleted acid hydrolysate of the milk protein casein.

He was born in London, UK and brought up in Hackney, the third child of Jewish immigrant parents from northern Romania. He gained scholarships to study for a degree in chemistry, achieving First Class Honours, and subsequently for a PhD at University College London, UCL.

In 1947 he secured an Imperial Chemical Industries (ICI) funded post as Research Fellow at Great Ormond Street Hospital, GOSH, initially to study tyrosine metabolism in premature babies. At that time the general view was that PKU was untreatable. In what could now be considered translational research, a bridge between science and clinical practice, Louis had a “light bulb” moment at a biochemistry meeting in which a more economical growth medium for a bacteriological test for amino acids was suggested during a discussion. Individual, pure amino acids were expensive at that time whereas amino acids produced from protein hydrolysates prepared by treatment with acid were much less so. Selective removal of phenylalanine and some other amino acids from a hydrolysate by filtering through charcoal was described at the meeting. Louis thought that by adding other essential nutrients this could form a suitable liquid protein substitute food for PKU patients. Moreover he was aware of a source of a protein, casein, hydrolysate from Allen and Hanbury's as he had worked in their pharmaceutical research laboratory in 1944. By potentially lowering the phenylalanine in the blood of PKU patients this artificial diet could test the hypothesis that the main cause of disability was their abnormally high phenylalanine. Louis was unsuccessful in persuading paediatricians at GOSH to trial this.

On one of his several visits to see Louis from his post at Birmingham Children's Hospital, the German doctor, Horst Bickel enquired whether Louis could think of a way to treat PKU. Louis described his concept and whilst allegedly sceptical, Bickel successfully treated a 2 year old girl with PKU in Birmingham this way. This was a world first with a lasting legacy.

Less well known is Louis' conviction since his time at GOSH that newborn screening would likely improve PKU outcomes by allowing earlier treatment. Urine testing appeared a simple and non‐invasive way to do this. At a chance meeting in London he discussed the idea with Senior Medical Officer in Public Health, Dr Nancy Gibbs, from Wales. This conversation led to the first community based urine screening programme of a cohort of the general newborn population in Cardiff from 1958 to 1959. This was another world first.

From evaluation of UK urine screening schemes it became apparent that urine testing was not sufficiently reliable. The conclusion and recommendation of expert groups in 1968 of which Louis was a member was that blood analysis with the heel prick test we are now so familiar with was more satisfactory.

Louis' published work had become noticed internationally and in 1968 he was offered a post as Associate Professor at the University of British Columbia which he took up, with promotion to Professor following 6 years later in 1974. He published extensively with over 120 papers to his name, a book on renal tubular dysfunction and he contributed to books, conferences and supervised research students, notably Savio L‐C Woo on the isolation and properties of human liver phenylalanine hydroxylase. He retired in 1984 after a 16 year teaching and research career at UBC.

A shy and modest man he was devoted to his family. His wife Frances died in 1991 and Louis is survived by his only daughter Lesley, grandsons Benjamin and Oliver and his youngest brother, Henry. He was beautifully spoken in a refined, old‐fashioned British way with an astonishing memory to the end. Generous to people who criticised him he quietly stood his ground, recognising that valid debate is integral to scientific discovery. And like many another innovative scientist it is in this way that he triumphed over sceptical adversity to leave a legacy in pioneering the successful treatment of PKU.

Kate Hall.

International Society for Neonatal Screening.