Many cases of Aase syndrome occur without a known reason and are not passed down through families (inherited). However, some cases have been shown to be inherited. These are due to a change in 1 of 20 genes important for making protein correctly (the genes make ribosomal proteins).

This condition is similar to Diamond-Blackfan anemia, and the two conditions should be considered the same. A missing piece on chromosome 19 is found in some people with Diamond-Blackfan anemia.

The anemia in Aase syndrome is caused by poor development of the bone marrow, which is where blood cells are formed.

Symptoms may include:

• Absent or small knuckles
• Cleft palate
• Deformed ears
• Droopy eyelids
• Inability to fully extend the joints from birth
• Narrow shoulders
• Pale skin
• Triple-jointed thumbs

Your health care provider will perform a physical exam. Tests that may be done include:

• Bone marrow biopsy
• Complete blood count (CBC)
• X-rays

Treatment may involve blood transfusions in the first year of life to treat anemia.

A steroid medicine called prednisone has also been used to treat anemia associated with Aase syndrome. However, it should only be used after reviewing the benefits and risks with a provider who has experience treating anemias.

A bone marrow transplant may be necessary if other treatment fails.

The anemia tends to improve with age.

Complications related to anemia include:

• Fatigue
• Decreased oxygen in the blood
• Weakness

Heart problems can lead to a variety of complications, depending on the specific defect.

Severe cases of Aase syndrome have been associated with stillbirth or early death.

Genetic counseling is recommended if you have a family history of this syndrome and wish to become pregnant.

Aase-Smith syndrome; Hypoplastic anemia - triphalangeal thumbs; Aase-Smith type; Diamond-Blackfan with AS-II; Aase-Smith I syndrome; Hydrocephalus-cleft palate-joint contractures syndrome; Aase-Smith syndrome type 1

Jones KL, Jones MC, del Campo M. Limb defect as major feature. In: Jones KL, Jones MC, del Campo M, eds. Smith's Recognizable Patterns of Human Malformation. 8th ed. Philadelphia, PA: Elsevier; 2022:428-459.

National Institutes of Health. National Center for Advancing Translational Sciences. Genetic and Rare Diseases Information Center website. Aase-Smith syndrome. rarediseases.info.nih.gov/diseases/5642/aase-smith-syndrome. Updated July 2025. Accessed August 1, 2025.

Thornburg CD. Congenital hypoplastic anemia (Diamond-Blackfan anemia). In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 497.

Updated by: Anna C. Edens Hurst, MD, MS, Associate Professor in Medical Genetics, The University of Alabama at Birmingham, Birmingham, AL. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.