Expanded mutational spectrum in Cohen syndrome, tissue expression, and transcript variants of COH1.

Cohen syndrome is characterised by mental retardation, postnatal microcephaly, facial dysmorphism, pigmentary retinopathy, myopia, and intermittent neutropenia. Mutations in COH1 (VPS13B) have been found in patients with Cohen syndrome from diverse ethnic origins. We have carried out mutation analysis in twelve novel patients with Cohen syndrome from nine families. In this series, we have identified 13 different mutations in COH1, twelve of these are novel including six frameshift mutations, four nonsense mutations, two splice site mutations, and a one-codon deletion. Since different transcripts of COH1 have been reported previously, we have analysed the expression patterns of COH1 splice variants. The transcript variant NM_152564 including exon 28b showed ubiquitous expression in all examined human tissues. In contrast, human brain and retina showed differential splicing of exon 28 (NM_017890). Moreover, analysis of mouse tissues revealed ubiquitous expression of Coh1 homologous to human NM_152564 in all examined tissues but no prevalent alternative splicing.

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.

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.

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 girl's 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.

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.

Cerebellar ataxia with progressive improvement.

BACKGROUND: Nonprogressive cerebellar ataxias are characterized by a persistent, nonprogressive ataxia associated with cognitive impairment. Cerebellar hypoplasia on imaging is variable but is not predictive of the degree of ataxia or cognitive impairment. OBJECTIVE: To describe a family with a nonprogressive cerebellar ataxia associated with cognitive and motor impairments that improve with age. DESIGN: Genetic study in a family with nonprogressive cerebellar ataxia. Clinical and imaging features are also described. SETTING: Community hospital. PATIENTS: Both parents and 3 children from an affected family. MAIN OUTCOME MEASURES: Clinical features, magnetic resonance imaging findings, and genetic findings. RESULTS: A genome-wide single nucleotide polymorphism screen did not show clear linkage to known spinocerebellar ataxia loci, in particular spinocerebellar ataxia type 15. Repeat spinocerebellar ataxia loci expansions were excluded. Magnetic resonance images of all affected individuals demonstrated cerebellar vermian abnormalities. CONCLUSIONS: These findings suggest that nonprogressive cerebellar ataxia is genetically heterogeneous and, when associated with gradual improvement in cognition and motor skills, likely represents a separate, distinct clinical entity.

Bilateral periventricular heterotopias in an X-linked dominant transmission in a family with two affected males.

We report on the case of dizygotic twin boys, born prematurely to an asymptomatic mother. Bilateral periventricular heterotopias with enlarged ventricles were discovered at birth in both twins. One of the twins died prematurely of bronchopulmonary complications, and was shown to have several neuropathological anomalies (microgyria, thin corpus callosum, and reduced white matter). The surviving twin had mental retardation, without epilepsy. MRI of the mother showed asymptomatic periventricular heterotopias without ventricular enlargement. She had two affected daughters also with asymptomatic periventricular heterotopias. A point mutation in the last coding exon 48 of the Filamin A (FLNA) gene (7922c > t) was discovered on sequencing and segregated with the affected individuals. This family has a classical X-linked dominant BPNH pathology, with greater severity in males than females. The location of the FLNA mutation is discussed in light of the neuropathological anomalies and mental retardation in male patients.

EMX2-independent familial schizencephaly: clinical and genetic analyses.

Schizencephaly is a human brain malformation distinguished by full-thickness unilateral or bilateral clefts through the neocortex. Heterozygous mutations in the EMX2 locus are reported to give rise to schizencephaly. However, the comprehensive identification of causative genetic loci is precluded by a lack of large pedigrees and genome-wide linkage analyses. We present here a large Turkish pedigree with three individuals with schizencephaly. The similarity of clinical signs in affected individuals strongly suggests an underlying genetic cause; however, genome-wide linkage analysis rules out EMX2 linkage and instead suggests additional candidate loci. These results indicate that genetic forms of schizencephaly are likely to be heterogeneous.

Community involvement in developing policies for genetic testing: assessing the interests and experiences of individuals affected by genetic conditions.

Because the introduction of genetic testing into clinical medicine and public health creates concerns for the welfare of individuals affected with genetic conditions, those individuals should have a role in policy decisions about testing. Mechanisms for promoting participation range from membership on advisory committees to community dialogues to surveys that provide evidence for supporting practice guidelines. Surveys can assess the attitudes and the experiences of members of an affected group and thus inform discussions about that community's concerns regarding the appropriate use of a genetic test. Results of a survey of individuals affected with inherited dwarfism show how data can be used in policy and clinical-practice contexts. Future research of affected communities' interests should be pursued so that underrepresented voices can be heard.

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.