TCF4 and Pitt-Hopkins syndrome: Prompted by the known role of TCF4 in muscle cell differentiation [5] (and the evidence that cancer cachexia is promoted by TCF4 which modulates expression of muscle atrophy promoting hormones [20], we – in the light of muscle weakness present in our patient – elucidated skeletal muscle vulnerability in PTHS by making use of a quadriceps biopsy.