Definitive diagnosis of BFLS is made with a genetic test, though it can be suspected where there are several people in a family showing the characteristic symptoms. Magnetic resonance imaging, electroencephalography, and electroneuronography can be used to assess the severity of the disease. Mutations in the PHF6 gene have been shown to be the cause of this condition. Other diseases that may need to be distinguished from BFLS include Prader–Willi syndrome, Coffin–Lowry syndrome, Klinefelter syndrome, Wilson–Turner syndrome, Bardet–Biedl syndrome, Smith–Fineman–Myers syndrome (Chudley-Lowry syndrome), and Coffin–Siris syndrome.
Börjeson–Forssman–Lehmann syndrome
Wallis–Zieff–Goldblatt syndrome
Hamman's syndrome
Zieve's syndrome
Ho–Kaufman–Mcalister syndrome
Grinspan's syndrome
Susac's syndrome
Bertolotti's syndrome