Aase syndrome is thought to be inherited in some manner but no one’s really quite sure. It’s certainly a genetic condition but doesn’t seem to run in families. It might thus be a recurrent mutation rather than something we normally think of as genetically heritable.

Aase syndrome is a rare genetic disorder that may be detected during
early infancy. The disorder is primarily characterized by the presence
of three bones (phalanges) within the thumbs (triphalangeal thumbs)
rather than the normal two and abnormally reduced production of red
blood cells (hypoplastic anemia). In some instances, additional
abnormalities may be present. The exact cause of Aase syndrome is
unknown. However, most evidence suggests that the disorder is inherited
as an autosomal recessive trait.

As you can see there’s still some controvery over the causes of Aase syndrome:

Most 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 as an autosomal dominant and autosomal recessive  traitn.

The anemia associated with Aase syndrome is caused by
underdevelopment of the bone marrow, which is where blood cells are
formed.

Possible (although not necessary) symptoms include:

• Absent or small knuckles
• Cleft palate
• Decreased skin creases at finger joints
• Deformed ears
• Delayed closure of fontanelles (soft spots)
• Droopy eye lids
• Inability to fully extend the joints from birth (contracture deformity)
• Mildly slowed growth
• Narrow shoulders
• Pale skin
• Triple-jointed thumbs

Surprisingly, given adequate treatment, Aase syndrome can be successfully treated. Bllod transfuions in the first year of life, drugs later, and it is known that the anaemia itself improves over time on it’s own. It is possible that bone marrow transplants will be required though.

A good source of further information is:

Genetic and Rare Diseases (GARD) Information Center
PO Box 8126
Gaithersburg, MD 20898-8126
Tel: (301)519-3194
Fax: (240)632-9164
Tel: (888)205-2311
TDD: (888)205-3223
Email: gardinfo@nih.gov
Internet: http://www.genome.gov/100000409   or http://rarediseases.info.nih.gov/html/resources/info_cntr.html