Congenital macrothrombocytopenia (CMTP) is a heterogeneous group of rare platelet disorders characterized by a congenital reduction of platelet counts and abnormally large platelets, for which CMTP-causing mutations are only found in approximately half the cases. We herein performed whole-exome sequencing and targeted Sanger sequencing to identify mutations that cause CMTP, in which a dominant mode of transmission had been suspected but for which no known responsible mutations have been documented. In 13 Japanese CMTP-affected pedigrees, we identified six (46%) affected by ACTN1 variants cosegregating with CMTP. In the entire cohort, ACNT1 variants accounted for 5.5% of the dominant forms of CMTP cases and represented the fourth most common cause in Japanese individuals. Individuals with ACTN1 variants presented with moderate macrothrombocytopenia with anisocytosis but were either asymptomatic or had only a modest bleeding tendency. ACTN1 encodes α-actinin-1, a member of the actin-crosslinking protein superfamily that participates in the organization of the cytoskeleton. In vitro transfection experiments in Chinese hamster ovary cells demonstrated that altered α-actinin-1 disrupted the normal actin-based cytoskeletal structure. Moreover, transduction of mouse fetal liver-derived megakaryocytes with disease-associated ACTN1 variants caused a disorganized actin-based cytoskeleton in megakaryocytes, resulting in the production of abnormally large proplatelet tips, which were reduced in number. Our findings provide an insight into the pathogenesis of CMTP.

The purpose of this study is to present the first report of a case of primary frosted branch angiitis from the UK and to review the characteristics of this rare disease. Primary frosted branch angiitis causes characteristic florid translucent retinal perivascular sheathing of both arterioles and venules in association with variable uveitis, retinal oedema and visual loss, normally with good recovery. A total of 57 cases have been reported in the world literature. Atypical, typically focal frosted branch angiitis may also occur secondary to other causes of intraocular inflammation, especially cytomegalovirus retinitis. Primary frosted branch angiitis has a characteristic presentation but a variable course, typically affecting children or young adults. The disease is likely to represent a common immune pathway in response to multiple infective agents. The optimal treatment is unclear.

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Our data indicate that HSCT for patients with GOF-STAT1 mutations is curative but has significant risk of secondary graft failure and death.

The prognosis of infants with acute lymphoblastic leukemia (ALL), particularly those with KMT2A gene rearrangement (KMT2A-r), is dismal. Continuous efforts have been made in Japan to investigate the role of stem cell transplantation (HSCT) for infants with KMT2A-r ALL, but improvement in outcomes was modest. In the Japanese Pediatric Leukemia/Lymphoma Study Group trial MLL-10 (registered at umin.ac.jp as UMIN000004801), infants with ALL were stratified into three risk groups (low-risk, LR; intermediate-risk, IR; high-risk, HR) according to KMT2A status, age, and presence of central nervous system leukemia. A modified Children's Oncology Group AALL0631 chemotherapy with addition of high-dose cytarabine in early intensification was introduced to KMT2A-r patients, and the option of HSCT was restricted to HR patients. The role of minimal residual disease (MRD) was also evaluated. Ninety eligible infants were stratified into LR (N=15), IR (N=19), or HR (N=56). The 3-year event-free survival (EFS) rate (standard error) for patients with KMT2A-r ALL (IR+HR) was 66.2% (5.6%) and 93.3% (6.4%) for those with KMT2A-g ALL (LR). The 3-year EFS rate was 94.4% (5.4%) for IR and 56.6% (6.8%) for HR patients. In multivariable analysis, female sex and MRD ≧0.01% at end of early consolidation were significant poor prognostic factors. Risk stratification and introduction of intensive chemotherapy in the current study were effective and able to eliminate HSCT for a subset of infants with KMT2A-r ALL. Early clearance of MRD seems to have translated into favorable outcomes and should be incorporated into risk stratifications in future trials.