FLNA p.V528M substitution is neither associated with bilateral periventricular nodular heterotopia nor with macrothrombocytopenia

Xq26.1-26.2 gain identified on array comparative genomic hybridization in bilateral periventricular nodular heterotopia with overlying polymicrogyria

Periventricular nodular heterotopia (PNH) with overlying polymicrogyria (PMG) is a recently described, developmental brain malformation; however, the causative genes of this malformation have not yet been identified. We report on a 5-year-old Japanese male with bilateral PNH with overlying PMG. He had mild intellectual disability, distinctive facial features, short stature, and microcephaly, with cardiac disorders. No mutation was identified in Sanger sequences for FLNA and ARFGEF2; however, array comparative genomic hybridization revealed an approximately 0.8Mb gain at Xq26.1-26.2, which included three genes: IGSF1, OR13H1, and FIRRE. We identified the same 3-copy gain in his mother; despite identifying the same abnormality in the mother, it must still be considered as a possible cause for the abnormalities, as X-inactivation in the mother could have led to her not expressing the same phenotype. This case may provide important clues for identifying the genes responsible and help in the understanding of the pathogenesis of this disorder.

Massively parallel sequencing of patients with intellectual disability, congenital anomalies and/or autism spectrum disorders with a targeted gene panel

Developmental delay and/or intellectual disability (DD/ID) affects 1–3% of all children. At least half of these are thought to have a genetic etiology. Recent studies have shown that massively parallel sequencing (MPS) using a targeted gene panel is particularly suited for diagnostic testing for genetically heterogeneous conditions. We report on our experiences with using massively parallel sequencing of a targeted gene panel of 355 genes for investigating the genetic etiology of eight patients with a wide range of phenotypes including DD/ID, congenital anomalies and/or autism spectrum disorder. Targeted sequence enrichment was performed using the Agilent SureSelect Target Enrichment Kit and sequenced on the Illumina HiSeq2000 using paired-end reads. For all eight patients, 81–84% of the targeted regions achieved read depths of at least 20×, with average read depths overlapping targets ranging from 322× to 798×. Causative variants were successfully identified in two of the eight patients: a nonsense mutation in the ATRX gene and a canonical splice site mutation in the L1CAM gene. In a third patient, a canonical splice site variant in the USP9X gene could likely explain all or some of her clinical phenotypes. These results confirm the value of targeted MPS for investigating DD/ID in children for diagnostic purposes. However, targeted gene MPS was less likely to provide a genetic diagnosis for children whose phenotype includes autism.

New insights into the versatile roles of platelet FlnA

Recent findings have identified critical roles for the actin filament-crosslinking protein filamin A (FlnA) in platelets and megakaryocytes. This short review focuses on the structure of FlnA and its interaction with the Von Willebrand Factor receptor GPIb-IX-V complex and the fibrinogen receptor, the integrin αIIbβ3 in platelets.

Unusual ribbon-like periventricular heterotopia with congenital cataracts in a Japanese girl

Periventricular heterotopia (PH), clumps of neurons mislocated beside the ventricle, is caused by failure to initiate migration during embryogenesis. We report on a 32-month-old Japanese girl with a unique subtype of PH, namely ribbon-like PH. The patient presented with severe psychomotor developmental delay, intractable epilepsy, and congenital cataracts and developed West syndrome phenotype. Brain magnetic resonance imaging revealed a unique undulating form of PH, categorized as ribbon-like PH, and other brain malformations including simplified gyri and dysgenesis of the corpus callosum. There was no evidence of prenatal TORCH infection or associated syndrome. Array-based comparative genomic hybridization revealed no chromosomal rearrangements. Genetic analyses of the FLNA, DCX, ARX, LIS1, and TUBA1A genes showed no mutations. Although little is known about ribbon-like PH, the clinical manifestations in our patient clearly differed from those in other reported patients.

FlnA-null megakaryocytes prematurely release large and fragile platelets that circulate poorly

Filamin A (FlnA) is a large cytoplasmic protein that crosslinks actin filaments and anchors membrane receptors and signaling intermediates. FlnA(loxP) PF4-Cre mice that lack FlnA in the megakaryocyte (MK) lineage have a severe macrothrombocytopenia because of accelerated platelet clearance. Macrophage ablation by injection of clodronate-encapsulated liposomes increases blood platelet counts in FlnA(loxP) PF4-Cre mice and reveals the desintegration of FlnA-null platelets into microvesicles, a process that occurs spontaneously during storage. FlnA(loxP) PF4-Cre bone marrows and spleens have a 2.5- to 5-fold increase in MK numbers, indicating increased thrombopoiesis in vivo. Analysis of platelet production in vitro reveals that FlnA-null MKs prematurely convert their cytoplasm into large CD61(+) platelet-sized particles, reminiscent of the large platelets observed in vivo. FlnA stabilizes the platelet von Willebrand factor receptor, as surface expression of von Willebrand factor receptor components is normal on FlnA-null MKs but decreased on FlnA-null platelets. Further, FlnA-null platelets contain multiple GPIbα degradation products and have increased expression of the ADAM17 and MMP9 metalloproteinases. Together, the findings indicate that FlnA-null MKs prematurely release large and fragile platelets that are removed rapidly from the circulation by macrophages.