- Arnold-Chiari malformation
- Arthrogryposis multiplex congenita
- Arthropathy-camptodactyly syndrome
- Asperger syndrome
- Asplenia
- Asthma
- Ataxia-telangiectasia
- Attention deficit hyperactivity disorder
- Autism
- Azorean disease
- Bardet-Biedl syndrome
- Batten disease
- Beals syndrome
- Beare-Stevenson cutis gyrata syndrome
- Beckwith-Wiedemann syndrome
- Beta thalassemia
- Bicuspid aortic valve
- Biotinidase deficiency
- Bipolar disorder
- Bloom syndrome
- Blue rubber bleb nevus syndrome
- Brachydactyly
- Branchiootorenal syndrome
- Breast cancer
- Bruton agammaglobulinemia
- Campomelic dysplasia
- Canavan disease
- Cancer
- Cardiofaciocutaneous syndrome
- Carnitine palmitoyltransferase deficiency
