NORD gratefully acknowledges Tatiana Garrison, MMSc, NORD Editorial Intern from the Emory University Genetic Counseling Training Program and Cecelia A. Bellcross, PhD, MS, CGC, Associate Professor, Director, Genetic Counseling Training Program, Emory University School of Medicine, for assistance in the preparation of this report.
Townes-Brocks syndrome (TBS) is a genetic condition caused by a harmful change (mutation) in a gene called SALL1. Features include no anal opening (imperforate anus) and differently shaped ears and thumbs. There can also be problems with the feet, heart and kidneys.
There are three major symptoms of TBS: A closed anal opening (imperforate anus), small ears that usually have a folded rim of skin and cartilage around the outer ear, and differences in the structures of the thumbs. The thumbs have three bones (triphalangeal) instead of two. People with this syndrome may also have an extra thumb (preaxial polydactyly). Another symptom may be hearing loss present at birth (congenital). The hearing loss can be sensorineural and/or conductive, range from mild to severe and may be progressive. Differences in the feet occur less frequently and include a short third toe, overlapping toes and flat feet. Typical kidney (renal) differences include displaced or rotated kidneys, horseshoe kidney, polycystic kidneys and underdeveloped kidneys. There can also be heart and genital problems present at birth. Intellectual disability occurs in about 10% of affected individuals.
TBS is caused by a harmful genetic change (mutation) in a gene called SALL1. The SALL1 gene has instructions for the body to form certain tissues and organs such as the hands (particularly the thumbs), ears, anus and kidneys. Humans should have two working copies of the SALL1 gene, but people with TBS have one copy of the gene that does not work properly.
There is also evidence that this condition could be caused by a mutation in the DACT1 gene, but a mutation in the SALL1 gene is the more common cause.
TBS is inherited in an autosomal dominant manner. Dominant genetic disorders occur when only a single copy of a non-working gene is necessary to cause a particular disease. The non-working gene can be inherited from either parent or can be the result of a changed (mutated) gene in the affected individual. The risk of passing the non-working gene from an affected parent to an offspring is 50% for each pregnancy. The risk is the same for males and females.
The clinical diagnosis of TBS is based on the presence of the three common symptoms (differences of the anus, ear and thumb) and sometimes the minor features. Genetic testing that reveals a harmful variant in the SALL1 gene can confirm the diagnosis.
Treatment includes surgery to correct the differences of the anus and thumbs. Hearing evaluation should be conducted if TBS is suspected. Ultrasound and laboratory tests should be performed to monitor kidney function. A baseline echocardiogram should be performed by a cardiologist.
Genetic counseling is recommended for affected individuals and their families.
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