Aase syndrome

Definition

Aase syndrome is a rare, autosomal recessive genetic disorder characterized by congenital hypoplastic anemia (CHA) and triphalangeal thumbs (TPT). People with Aase syndrome may have one or more physical abnormalities. Poor growth in childhood is common, but mental retardation and other neurological problems are not associated with Aase syndrome.

Description

Aase syndrome is sometimes also called Aase–Smith syndrome, or Congenital Anemia–Triphalangeal Thumb syndrome. It is a very rare hereditary syndrome involving multiple birth defects. The two symptoms that must be present to consider the diagnosis of Aase syndrome are CHA and TPT. CHA is a significant reduction from birth in the number of red cells in the blood. TPT means that one or both thumbs have three bones (phalanges) rather than the normal two.

Several other physical abnormalities have been described in individuals with Aase syndrome, including narrow shoulders, hypoplastic radius (underdevelopment of one of the bones of the lower arm), heart defect, cleft lip/palate, and late closure of the fontanelles (soft spots on an infant's skull where the bones have not yet fused). The specific cause of Aase syndrome is not known, but recurrence of the condition in siblings implies an abnormal gene is responsible.

Genetic profile

The available evidence suggests Aase syndrome is inherited in an autosomal recessive fashion, meaning that an affected person has two copies of the abnormal gene. Parents of an affected individual carry one abnormal copy of that particular gene, but their other gene of the pair is normal. One copy of the normal gene is sufficient for the parent to be unaffected. If both parents are carriers of a gene for the same autosomal recessive condition, there is a one in four chance in each pregnancy that they will both pass on the abnormal gene and have an affected child.

Autosomal recessive inheritance is suspected for Aase syndrome based on the pattern seen in the families that have been described. An autosomal recessive pattern requires that only siblings are affected by the condition (parents are unaffected gene carriers), and the disorder occurs equally in males and females. An abnormal gene proven to cause Aase syndrome has not been discovered.

Demographics

Aase syndrome is quite rare, with possibly no more than two dozen cases reported in the medical literature.

Signs and symptoms

CHA and TPT are the two classic signs of Aase syndrome. The anemia may require treatment with steroids, or possibly blood transfusions, but tends to improve over time. TPT may cause a person with Aase syndrome to have difficulty grasping and manipulating objects with their hands. A hypoplastic radius may complicate problems with appearance and movement of the hands and arms. Narrow and sloping shoulders are caused by abnormal development of the bones in that area of the body.

Slow growth in children with Aase syndrome may be partly related to their anemia, but is more likely to be genetically predetermined due to the syndrome. Ventricular septal defect (VSD), a hole between the bottom two chambers of the heart, is the cardiac defect reported most often, and several cases of cleft lip and palate have occurred as well.

Diagnosis

The diagnosis of Aase syndrome is made when an infant has CHA and TPT, and one or more of the other symptoms. Children with another more common congenital anemia syndrome, Blackfan–Diamond syndrome (BDS), sometimes have abnormalities of their thumbs. Since the syndromes have overlapping symptoms, there is some question about whether Aase syndrome and BDS are contiguous gene syndromes or even identical conditions. Further genetic research may resolve this issue.

Treatment and management

Anemia associated with Aase syndrome is often helped by the use of a steroid medication. For serious anemia that does not respond to medications, blood transfusions from a matched donor might be necessary. Management of problems related to the skeletal abnormalities should be treated by orthopedic surgery as well as physical and occupational therapy. Heart defects and cleft lip and palate are nearly always correctable, but both require surgery and long–term follow up. A genetic evaluation and counseling should be offered to any individual or couple whose child is suspected of having Aase syndrome.

KEY TERMS

Hypoplastic radius

—Underdevelopment of the radius, the outer, shorter bone of the forearm.

Prognosis

While major medical procedures such as blood transfusions and corrective surgeries might be needed for a child with Aase syndrome, the long–term prognosis seems to be good. Discovery of the specific genetic defect is not likely to immediately change the prognosis. Development of a reliable genetic test, however, might allow for carrier testing for other family members, and prenatal diagnosis for couples who already have an affected child.

Resources

ORGANIZATIONS

Aicardi Syndrome Awareness and Support Group. 29 Delavan Ave., Toronto, ON M5P 1T2. Canada (416) 481-4095.

March of Dimes Birth Defects Foundation. 1275 Mamaroneck Ave., White Plains, NY 10605. (888) 663-4637. resourcecenter@modimes.org. <http://www.modimes.org>.

National Heart, Lung, and Blood Institute. PO Box 30105, Bethesda, MD 20824-0105. (301) 592-8573. nhlbiinfo@rover.nhlbi.nih.gov. <http://www.nhlbi.nih.gov>.

National Organization for Rare Disorders (NORD). PO Box 8923, New Fairfield, CT 06812-8923. (203) 746-6518 or (800) 999-6673. Fax: (203) 746-6481. <http://www.rarediseases.org>.

National Society of Genetic Counselors. 233 Canterbury Dr., Wallingford, PA 19086-6617. (610) 872-1192. <http://www.nsgc.org/GeneticCounselingYou.asp>.

Scott J. Polzin, MS, CGC