The X chromosome is full of surprises and if the future of the field is anything like the last few years, it would seem we have much to look forward to. Papers of particular interest, published within the period of review, have been highlighted as: • of special interest This work was supported by NIH/NHGRIT32 this website HG000044 and U01-HL100397. “
“Current Opinion in Genetics & Development 2013, 23:316–323 This review comes from a themed issue on Molecular and genetic bases of disease Edited by Jim Lupski and Nancy Maizels For a complete overview see the Issue and the Editorial Available online 17th April 2013 0959-437X/$

– see front matter, © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.gde.2013.02.015 Thrombocytopenia with absent radii (TAR) syndrome is characterized by a reduction in the number of platelets (the cells that make the blood clot) (generally below 50 × 109 L−1, normal range 150–350 × 109 L−1) and the absence of one of the bones in the forearm (the radius) but with preservation of the thumb. TAR syndrome was first described by Gross et al. [ 1] and Shaw and Oliver in 1959 [ 2], but Judith Hall was the first to define it as a syndrome in 1969, presenting

clinical findings in a cohort of 40 patients [ 3]. The presence of the thumbs distinguishes TAR from other syndromes that combine blood abnormalities with absence of the radius, such as Fanconi anemia [ 3, 4 and 5]. The severity of skeletal abnormalities varies from absence GSK3 inhibitor of radii to virtual absence of upper limbs (phocomelia) with or without lower limb defects, such as malformations of the hip and knee [ 3 and 5]. TAR cases have low numbers of megakaryocytes, the platelet precursor cells that reside in the bone marrow, and cases frequently present with bleeding episodes in the either first year of life [ 3 and 5]. A remarkable feature of TAR syndrome is that the platelet count can improve with

age and bleeding diminishes [ 5]. Other symptoms have been described in a series of 34 TAR patients [ 6], with renal anomalies and cardiac anomalies in respectively 23% and 15% of patients, and 47% suffering from intolerance to cow’s milk. TAR syndrome has an incidence of approximately 1 in 240 000 births [7] and was thought to be inherited as an autosomal recessive disease [8] based on finding affected siblings. There is however no clear evidence of increased incidence in consanguineous families with only one case reported [9]. On the other hand, vertical parent-to-child transmission has been reported [10], as well as the case of a male patient and maternal uncle [11]. This unusual inheritance pattern has complicated the application of classic linkage analysis methods and homozygosity mapping approaches.