CTBP1 and Hypotonia: Hypotonia, ataxia, developmental delay and tooth enamel defect syndrome (HADDTS; MIM: 617915) secondary to a recurrent de novo missense mutation in CTBP1 [NM_001012614.1:c.991C>T, p.(Arg331Trp)] was first reported by Beck et al.3They described four unrelated individuals with a neurodevelopmental phenotype consisting of early onset developmental delay, intellectual impairment, hypotonia, cerebellar dysfunction, poor weight gain, tooth enamel defects and variable changes on muscle biopsy.3