HTT and neurodevelopmental disorder: When considering lowering strategies, maintaining certain physiological levels of HTT is important—hypomorphic HTT mutations cause a neurodevelopmental disorder, LOMAR syndrome,43 and common HTT genetic variation linked to ageing and cognitive traits.19 The results of a new paradigm-changing study that performed paired single-cell gene expression and CAG-repeat length analysis in human Huntington’s disease brains also bring the field’s focus on HTT lowering under scrutiny.44 Firstly, striatal neuron loss did not correlate with HTT expression levels.