Meyahealth
HomeGeneticsConditionSADDAN
Back to Condition
SADDAN
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

SADDAN

SADDAN (severe achondroplasia with developmental delay and acanthosis nigricans) is a rare disorder of bone growth characterized by extremely short stature, profound developmental delay, and a progressive skin condition, caused by mutations in the FGFR3 gene.

Overview

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.

Frequency

This disorder is very rare; it has been described in only a small number of individuals worldwide.

Causes

Mutations in the FGFR3gene cause SADDAN. The FGFR3gene 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.

Learn more about the gene associated with SADDAN

  • FGFR3

Inheritance

SADDAN is considered an autosomal dominant disorder because one mutated copy of the FGFR3gene in each cell is sufficient to cause the condition. The few described cases of SADDAN have been caused by new mutations in the FGFR3gene 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

  • Achondroplasia, severe, with developmental delay and acanthosis nigricans
  • SADDAN dysplasia
  • Severe achondroplasia with developmental delay and acanthosis nigricans
  • Skeleton-skin-brain syndrome
  • SSB syndrome

Frequently Asked Questions

Diagnosis relies on clinical features (severe short stature, limb bowing, acanthosis nigricans, developmental delay) plus molecular confirmation. A targeted FGFR3 gene analysis or a clinical exome panel that includes FGFR3 will detect the characteristic activating mutation (often p.Lys650Glu). Chromosomal microarray is not useful for this point mutation. Testing should be performed in a certified genetics laboratory, and results are interpreted by a geneticist or genetic counselor.
Management is multidisciplinary. Serial casting or guided growth (hemiepiphysiodesis) can reduce progressive bowing in early childhood. For severe deformities, corrective osteotomies are performed once the child is older (typically after age 5) to improve gait and reduce fracture risk. A pediatric pulmonologist should monitor chest wall restriction; in cases of severe thoracic insufficiency, a custom‑fitted brace or, rarely, thoracic expansion surgery may be considered. Physical therapy focusing on strengthening and range‑of‑motion is essential throughout.
Topical keratolytics (e.g., 12% ammonium lactate) and retinoids can soften the hyperpigmented plaques, but the skin changes often persist. Weight control and insulin‑sensitizing measures (dietary counseling, metformin if insulin resistance develops) are recommended because acanthosis nigricans can be a cutaneous marker of underlying metabolic dysfunction, even in SADDAN. Regular fasting glucose and HbA1c checks every 1–2 years are prudent.
Polysomnography should be performed early (by age 2–3) to quantify apnea‑hypopnea index. If significant central apnea is documented, nocturnal supplemental oxygen or non‑invasive positive pressure ventilation (BiPAP) may be prescribed. Parents should be educated on safe sleep positioning and the use of home pulse‑oximetry monitors. Ongoing follow‑up with a pediatric sleep specialist is advised, especially if developmental regression or daytime hypersomnolence occurs.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

Meyahealth

Ⓒ 2026. All rights reserved by MEYA

About UsTerms & PolicyFAQ