Kira Apse

Identifying Autism Loci and Genes by Tracing Recent Shared Ancestry

To find inherited causes of autism-spectrum disorders, we studied families in which parents share ancestors, enhancing the role of inherited factors. We mapped several loci, some containing large, inherited, homozygous deletions that are likely mutations. The largest deletions implicated genes, including PCDH10 (protocadherin 10) and DIA1 (deleted in autism1, or c3orf58), whose level of expression changes in response to neuronal activity, a marker of genes involved in synaptic changes that underlie learning. A subset of genes, including NHE9 (Na+/H+ exchanger 9), showed additional potential mutations in patients with unrelated parents. Our findings highlight the utility of “homozygosity mapping” in heterogeneous disorders like autism but also suggest that defective regulation of gene expression after neural activity may be a mechanism common to seemingly diverse autism mutations.

Importance of glucose-6-phosphate dehydrogenase activity in cell death.

The intracellular redox potential plays an important role in cell survival. The principal intracellular reductant NADPH is mainly produced by the pentose phosphate pathway by glucose-6-phosphate dehydrogenase (G6PDH), the rate-limiting enzyme, and by 6-phosphogluconate dehydrogenase. Considering the importance of NADPH, we hypothesized that G6PDH plays a critical role in cell death. Our results show that 1) G6PDH inhibitors potentiated H2O2-induced cell death; 2) overexpression of G6PDH increased resistance to H2O2-induced cell death; 3) serum deprivation, a stimulator of cell death, was associated with decreased G6PDH activity and resulted in elevated reactive oxygen species (ROS); 4) additions of substrates for G6PDH to serum-deprived cells almost completely abrogated the serum deprivation-induced rise in ROS; 5) consequences of G6PDH inhibition included a significant increase in apoptosis, loss of protein thiols, and degradation of G6PDH; and 6) G6PDH inhibition caused changes in mitogen-activated protein kinase phosphorylation that were similar to the changes seen with H2O2. We conclude that G6PDH plays a critical role in cell death by affecting the redox potential.The intracellular redox potential plays an important role in cell survival. The principal intracellular reductant NADPH is mainly produced by the pentose phosphate pathway by glucose-6-phosphate dehydrogenase (G6PDH), the rate-limiting enzyme, and by 6-phosphogluconate dehydrogenase. Considering the importance of NADPH, we hypothesized that G6PDH plays a critical role in cell death. Our results show that 1) G6PDH inhibitors potentiated H2O2-induced cell death; 2) overexpression of G6PDH increased resistance to H2O2-induced cell death; 3) serum deprivation, a stimulator of cell death, was associated with decreased G6PDH activity and resulted in elevated reactive oxygen species (ROS); 4) additions of substrates for G6PDH to serum-deprived cells almost completely abrogated the serum deprivation-induced rise in ROS; 5) consequences of G6PDH inhibition included a significant increase in apoptosis, loss of protein thiols, and degradation of G6PDH; and 6) G6PDH inhibition caused changes in mitogen-activated protein kinase phosphorylation that were similar to the changes seen with H2O2. We conclude that G6PDH plays a critical role in cell death by affecting the redox potential.

Filamin A mutations cause periventricular heterotopia with Ehlers-Danlos syndrome

Objective: To define the clinical, radiologic, and genetic features of periventricular heterotopia (PH) with Ehlers-Danlos syndrome (EDS). Methods: Exonic sequencing and single stranded conformational polymorphism (SSCP) analysis was performed on affected individuals. Linkage analysis using microsatellite markers on the X-chromosome was performed on a single pedigree. Western blotting evaluated for loss of filamin A (FLNA) protein and Southern blotting assessed for any potential chromosome rearrangement in this region. Results: The authors report two familial cases and nine additional sporadic cases of the EDS-variant form of PH, which is characterized by nodular brain heterotopia, joint hypermobility, and development of aortic dilatation in early adulthood. MRI typically demonstrated bilateral nodular PH, indistinguishable from PH due to FLNA mutations. Exonic sequencing or SSCP analyses of FLNA revealed a 2762 delG single base pair deletion in one affected female. Another affected female harbored a C116 single point mutation, resulting in an A39G change. A third affected female had a 4147 delG single base pair deletion. One pedigree with no detectable exonic mutation demonstrated positive linkage to the FLNA locus Xq28, an affected individual in this family also had no detectable FLNA protein, but no chromosomal rearrangement was detected. Conclusion: These results suggest that the Ehlers-Danlos variant of periventricular heterotopia (PH), in part, represents an overlapping syndrome with X-linked dominant PH due to filamin A mutations.

Reading impairment in the neuronal migration disorder of periventricular nodular heterotopia.

Objective: To define the behavioral profile of periventricular nodular heterotopia (PNH), a malformation of cortical development that is associated with seizures but reportedly normal intelligence, and to correlate the results with anatomic and clinical features of this disorder. Methods: Ten consecutive subjects with PNH, all with epilepsy and at least two periventricular nodules, were studied with structural MRI and neuropsychological testing. Behavioral results were statistically analyzed for correlation with other features of PNH. Results: Eight of 10 subjects had deficits in reading skills despite normal intelligence. Processing speed and executive function were also impaired in some subjects. More marked reading difficulties were seen in subjects with more widely distributed heterotopia. There was no correlation between reading skills and epilepsy severity or antiepileptic medication use. Conclusion: The neuronal migration disorder of periventricular nodular heterotopia is associated with an impairment in reading skills despite the presence of normal intelligence.

A structural basis for reading fluency: White matter defects in a genetic brain malformation

Background: Multiple lines of evidence have suggested that developmental dyslexia may be associated with abnormalities of neuronal migration or axonal connectivity. In patients with periventricular nodular heterotopia—a rare genetic brain malformation characterized by misplaced nodules of gray matter along the lateral ventricles—a specific and unexpected reading disability is present, despite normal intelligence. We sought to investigate the cognitive and structural brain bases of this phenomenon. Methods: Ten adult subjects with heterotopia, 10 with dyslexia, and 10 normal controls were evaluated, using a battery of neuropsychometric measures. White matter integrity and fiber tract organization were examined in six heterotopia subjects, using diffusion tensor imaging methods. Results: Subjects with heterotopia and those with developmental dyslexia shared a common behavioral profile, with specific deficits in reading fluency. Individuals with dyslexia seemed to have a more prominent phonological impairment than heterotopia subjects. Periventricular nodular heterotopia was associated with specific, focal disruptions in white matter microstructure and organization in the vicinity of gray matter nodules. The degree of white matter integrity correlated with reading fluency in this population. Conclusions: We demonstrate that a genetic disorder of gray matter heterotopia shares behavioral characteristics with developmental dyslexia, and that focal white matter defects in this disorder may serve as the structural brain basis of this phenomenon. Our findings represent a potential model for the use of developmental brain malformations in the investigation of abnormal cognitive function.

Perceptions of genetic discrimination among at-risk relatives of colorectal cancer patients

Purpose: To explore the concerns of at-risk relatives of colorectal cancer patients about genetic discrimination and their awareness of current legislative protections.Methods: A questionnaire was sent to unaffected individuals with a family history of colorectal cancer who had enrolled in the Johns Hopkins Hereditary Colorectal Cancer Registry (N = 777).Results: Of the 470 respondents, approximately half rated their level of concern about genetic discrimination as high. The majority of respondents, 79%, learned about genetic discrimination from at least one media source (television, newspapers, magazines, and radio). If they were to pursue genetic testing, respondents with a higher level of concern about genetic discrimination would be significantly more likely to pay out of pocket, use an alias, or ask for test results to be excluded from their medical record. Awareness and understanding of legislation regarding genetic discrimination was found to be minimal.Conclusion: Findings from this study demonstrate the negative effect of concerns about genetic discrimination on decisions about utilization of genetic services. Stronger legislative protections against genetic discrimination and increased public education through the scientific community and media sources are needed.

Periventricular nodular heterotopia and Williams syndrome.

We report here on the first case of a child with bilateral periventricular nodular heterotopia (PNH) and Williams syndrome. Fluorescent in situ hybridization (FISH) analyses demonstrated a deletion of the elastin gene in the Williams syndrome critical region (WSCR). Further mapping by loss of heterozygosity analysis both by microsatellite marker and SNP profiling demonstrated a 1.5 Mb deletion beyond the telomeric end of the typical WSCR. No mutations were identified in the X‐linked filamin‐A gene (the most common cause of PNH). These findings suggest another dominant PNH disorder along chromosome 7q11.23.

The Role of RELN in Lissencephaly and Neuropsychiatric Disease

Reelin is an extracellular matrix‐associated protein important in the regulation of neuronal migration during cerebral cortical development. Point mutations in the RELN gene have been shown to cause an autosomal recessive human brain malformation termed lissencephaly with cerebellar hypoplasia (LCH). Recent work has raised the possibility that reelin may also play a pathogenic role in other neuropsychiatric disorders. We sought, therefore, to define more precisely the phenotype of RELN gene disruption. To do this, we performed a clinical, radiological, and molecular study of a family in whom multiple individuals carry a chromosomal inversion that disrupts the RELN locus. A 6‐year‐old girl homozygous for the pericentric inversion 46,XX,inv7(p11.2q22) demonstrated the same clinical features that have been previously described in association with RELN point mutations. The girls brain magnetic resonance imaging (MRI) findings, including pachygyria and severe cerebellar hypoplasia, were identical to those seen with RELN point mutations. Fluorescence in situ hybridization confirmed that one of the breakpoints of this inversion mapped to within the RELN gene, and Western blotting revealed an absence of detectable serum reelin protein. Several relatives who were heterozygous for this inversion were neurologically normal and had no signs of psychotic illness. Our findings demonstrate the distinctive phenotype of LCH, which is easily distinguishable from other forms of lissencephaly. Although RELN appears to be critical for normal cerebral and cerebellar development, its role, if any, in the pathogenesis of psychiatric disorders remains unclear.

Comprehensive EMX2 genotyping of a large schizencephaly case series

Schizencephaly is a brain malformation disorder characterized by one or more full‐thickness clefts through the cerebral cortex. While initial reports suggested that EMX2 mutations are a common cause of schizencephaly, more recent evidence suggests that EMX2 mutations are not a common cause of this malformation. To determine the frequency of EMX2 mutations in patients with schizencephaly, we sequenced EMX2 in a cohort of 84 affected probands. No pathologic mutations were identified in this cohort, suggesting that EMX2 mutations are an uncommon cause of schizencephaly.

Broader geographical spectrum of Cohen syndrome due to COH1 mutations

It is overrepresented in Finland, though cases have been reported worldwide. The genetic locus for Cohen syndrome was mapped to chromosome 8q in several Finnish pedigrees. 34 Recently, a novel gene, COH1, in this locus was shown to carry mutations in many patients with Cohen syndrome. 5 COH1 is a large gene, consisting of 62 exons and encoding a protein of 4022 amino acids, whose biological function is not known. So far all the patients with reported mutation in the COH1 gene are of Finnish or other northern European origin. Therefore it has not been known if the COH1 gene is responsible for those cases of Cohen syndrome outside northern Europe. Here we report novel mutations in the COH1 gene in four non-Finnish (Omani, Saudi Arabian, Japanese, and French) pedigrees, demonstrating that COH1 mutations are respon- sible for Cohen syndrome in non-Finnish populations. Variable phenotypes among these patients supports the idea that non-Finnish Cohen syndrome due to COH1 mutations has a broader clinical spectrum than the Finnish subtype. We also perform the first expression analysis of the mouse COH1 homologue, in order to investigate the pathogenesis of microcephaly in Cohen syndrome.