Bachmann-Bupp syndrome (BABS) is a rare autosomal dominant condition caused by gain-of-function changes (pathogenic variants) in the ornithine decarboxylase-1 gene (ODC1) on chromosome 2p25. To date, fewer than 30 individuals have been reported with a pathogenic variant in ODC1. Thus, the phenotypic features associated with BABS are based on these reports.

BABS is characterized by a distinctive pattern of noncongenital alopecia; at birth, hair is sparse and of unexpected color and is lost in clumps within the first few weeks of life. Eyebrows and eyelashes may also be sparse.

Affected individuals may present with dysmorphic features, including bilateral ptosis, hypertelorism, retrognathia, and a bulbous nasal tip. Individuals may also present with moderate-to-severe developmental delays as well as feeding difficulties. Walking may be delayed, up to 17 months to 5 years. First words may be delayed until the ages of 3-6 years. Some patients have remained nonverbal, even into adolescence.

Individuals with BABS may present with behavioral conditions, such as attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and aggression. Macrocephaly and macrosomia are often seen in affected individuals.

Other findings have been variable. One case reported onset of seizures at age 14 years. Another reported congenital sensorineural hearing loss in one ear. Two cases presented with congenital heart disease. Two cases with brittle nails and underdeveloped (hypoplastic) toenails were reported. One case reported vision abnormalities associated with a curved cornea.