SADDAN (severe achondroplasia with developmental delay and acanthosis nigricans) is a rare disorder of bone growth characterized by skeletal, brain, and skin abnormalities.
All people with this condition have extremely short stature with particularly short arms and legs. Other features include unusual bowing of the leg bones; a small chest with short ribs and curved collar bones; short, broad fingers; and folds of extra skin on the arms and legs. Structural abnormalities of the brain cause seizures, profound developmental delay, and intellectual disability. Several affected individuals also have had episodes in which their breathing slows or stops for short periods (apnea). Acanthosis nigricans, a progressive skin disorder characterized by thick, dark, velvety skin, is another characteristic feature of SADDAN that develops in infancy or early childhood.
This disorder is very rare; it has been described in only a small number of individuals worldwide.
Mutations in the FGFR3 gene cause SADDAN. The FGFR3 gene provides instructions for making a protein that is involved in the development and maintenance of bone and brain tissue. A mutation in this gene may cause the FGFR3 protein to be overly active, which leads to the disturbances in bone growth that are characteristic of this disorder. Researchers have not determined how the mutation disrupts brain development or causes acanthosis nigricans.
SADDAN is considered an autosomal dominant disorder because one mutated copy of the FGFR3 gene in each cell is sufficient to cause the condition. The few described cases of SADDAN have been caused by new mutations in the FGFR3 gene and occurred in people with no history of the disorder in their family. No individuals with this disorder are known to have had children; therefore, the disorder has not been passed to the next generation.
Other Names for This Condition
- achondroplasia, severe, with developmental delay and acanthosis nigricans
- SADDAN dysplasia
- Severe achondroplasia with developmental delay and acanthosis nigricans
- Skeleton-skin-brain syndrome
- SSB syndrome
Additional Information & Resources
Genetic Testing Information
Genetic and Rare Diseases Information Center
Catalog of Genes and Diseases from OMIM
Scientific Articles on PubMed
- Bellus GA, Bamshad MJ, Przylepa KA, Dorst J, Lee RR, Hurko O, Jabs EW, Curry CJ, Wilcox WR, Lachman RS, Rimoin DL, Francomano CA. Severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN): phenotypic analysis of a new skeletal dysplasia caused by a Lys650Met mutation in fibroblast growth factor receptor 3. Am J Med Genet. 1999 Jul 2;85(1):53-65. Citation on PubMed
- Cohen MM Jr. Some chondrodysplasias with short limbs: molecular perspectives. Am J Med Genet. 2002 Oct 15;112(3):304-13. Review. Citation on PubMed
- Kumar KV, Shaikh A, Sharma R, Prusty P. SADDAN syndrome. J Pediatr Endocrinol Metab. 2011;24(9-10):851-2. Citation on PubMed
- Vajo Z, Francomano CA, Wilkin DJ. The molecular and genetic basis of fibroblast growth factor receptor 3 disorders: the achondroplasia family of skeletal dysplasias, Muenke craniosynostosis, and Crouzon syndrome with acanthosis nigricans. Endocr Rev. 2000 Feb;21(1):23-39. Review. Citation on PubMed
- Zankl A, Elakis G, Susman RD, Inglis G, Gardener G, Buckley MF, Roscioli T. Prenatal and postnatal presentation of severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN) due to the FGFR3 Lys650Met mutation. Am J Med Genet A. 2008 Jan 15;146A(2):212-8. Citation on PubMed