TAR syndrome

Prenatal

diagnosis and post-mortem examination in a fetus with thrombocytopenia-absent radius (TAR) syndrome due to compound heterozygosity for a 1q21.1 microdeletion and a RBM8A hypomorphic allele: a case report. Clinical and radiologic findings. Frontal (A) and right lateral (B) views of the fetus showing flat nasal bridge with midly anteverted nares and receding chin. Severely shortened forearms, radial club hands and presence of thumbs. Magnification of the left hand (C) shows camptodactyly with bulbous ends, pterygium between wrist and the rhizomelic segment, and normally placed thumb. Babygram confirms the absence of both radii with hypoplastic and straight ulnae (D). Note normal ossification of the acral segment.

bmcresnotes.biomedcentral.com • CC-by-2.0

Thrombocytopenia

and absent radii (TAR) syndrome associated with bilateral congenital cataract: a case report. Clinical signs and X-ray findings in the baby girl. (A) Radial deviation of the right upper limb with no thumb deformity. (B) Multiple purpuric eruptions in the anterior aspect of the right lower limb. (C) X-ray of the left upper limb showing absent radius.

jmedicalcasereports.biomedcentral.com • CC-by-2.0

AP radiograph

of the upper limb showing absent radius with radially deviated hand

Wikipedia • CC BY 2.0

Thrombocytopenia

with absent radius syndrome • Thrombocytopenia with absent radius (TAR) syndrome - Ganzer Fall bei Radiopaedia

Ranchod A, Thrombocytopenia with absent radius (TAR) syndrome. Case study, Radiopaedia.org (Accessed on 12 Dec 2022) https://doi.org/10.53347/rID-150965 • CC by-nc-sa 3.0 (modified)

Radiopaedia • CC-by-nc-sa 3.0 • de

Thrombocytopenia with absent radius (TAR) syndrome is primarily characterized by the following two features:

fetal thrombocytopenia
absent fetal radii (bilaterally) with the presence of both thumbs

Epidemiology

The condition is extremely rare with an estimated incidence of 0.4 per 100,000 births.

Pathology

The principal defect is thought to absent or arrested development of the megakaryocyte progenitor cell or a progenitor cell with a maturational defect as there is minimally deleted region on chromosome 1q21.1 (deletion/duplication syndrome).

Genetics

It is thought to carry an autosomal recessive inheritance with variable penetrance .

Associations

cleft lip +/- palate
congenital cardiac anomalies in ~30%
jaw under development: micrognathia
partial absence of lower limbs
- fibula aplasia: ~50%

Radiographic features

Antenatal ultrasound

Sonographic features include:

bilateral absence of radii with normal thumbs (crucial to the diagnosis)
radial deviation of the hands
the ulna is abnormal (usually shortened and malformed but may be absent bilaterally in ~20% of cases and unilaterally in ~10% of cases).
the humerus is abnormal in almost 50% of cases and absent bilaterally (humeral aplasia) in 5-10% of cases (a five fingered hand arises from the shoulder)
asymmetrical limb shortening, abnormalities of the shoulder joint and hypoplasia of the glenoid fossa, scapulae and clavicles and soft tissues of the arm and shoulder have been reported
synostosis of the metacarpal bones
hypoplastic digits

Treatment and prognosis

Although the TAR syndrome is not uniformly fatal, early prenatal diagnosis is important as the morbidity and mortality associated with this condition may be high. The prognosis is thought to be good if the patient survives to at least one year of age where there is improvement of the thrombocytopenia.

Management options include intrauterine platelet transfusion to prevent fetal hemorrhage in labor; a planned atraumatic delivery (cesarean section) or termination of pregnancy in the second trimester may be contemplated.

Complications

intracranial hemorrhage: especially during the 1 year of life can impair mental development

History and etymology

The TAR syndrome was initially described by H Gross et al. in 1956 .

Differential diagnosis

The following diseases show radial hypoplasia as a component manifestation: