A

Absent thumb with radial-ray deformity and thrombocytopenia points toward Fanconi anaemia rather than the TAR syndrome (in which thumbs are always present) [Hall, 1969, PMID 4951233]. Work-up for Fanconi requires hematologic evaluation (platelet count), bone-marrow examination and cytogenetic/karyotype studies to detect chromosomal breakage, but echocardiography is not a routine diagnostic test for this condition [Merrill, 2005, PMID 15662710].