Clinicians should pay particular attention to developmental delays or learning difficulties and to attention problems in children with severe CH (athyreosis, absent knee epiphyses at term, very low T4 and very high TSH concentrations at diagnosis) or poor endocrine control, particularly during the first year, and in those from economically disadvantaged families (1|⊕⊕⊕). Here, CD4 is linked to cyclic hematopoiesis.