Bardet-Biedl and Cohen syndromes: differential diagnostic criteria.

EDITOR—Fig 1 in the paper by Beales et al shows portraits of six patients with the Bardet-Biedl syndrome (BBS). Number 4, the lower left picture, has the facial appearance of the Cohen syndrome (CS) with apparent microcephaly, thick hair, coarse eyebrows, short philtrum, and prominent incisors. Since she is presented as a case of the BBS, she should have a rod-cone retinal dystrophy and other signs of BBS. The diVerential diagnosis between BBS and CS is so far a clinical one. Both disorders present rod-cone dystrophy from an early age, obesity, and often speech disorders/ delay. 2 The diVerences between the two are renal anomalies, male hypogenitalism, radiographic poly/syndactyly, and normal intelligence to mild intellectual disability in BBS. 3 In CS, there are short, thin fingers and metacarpals, obesity localised to the abdomen, thin arms and legs, moderate to severe developmental delay, and characteristic facial features. Granulocytopenia is almost always observed in CS when a series of blood smears are examined. 5 There are dental malformations in both syndromes; CS shows large incisors and BBS has short roots. In a study of BBS based on questionnaires, there is a risk of underestimating the number of patients with CS. To avoid this risk we suggest that the above mentioned diagnostic features of CS should be included as diVerential diagnostic criteria.