Novel assay for Roberts syndrome assigns variable phenotypes to one complementation group

Report of the Phenotype of a Patient with Roberts Syndrome and a Rare ESCO2 Variant

Roberts syndrome is a rare autosomal recessive genetic disease. In this report, we report a Brazilian patient with a rare ESCO2 variant. The patient manifested a broad range of clinical findings including the significant, bilateral shortening of the extremities. He deteriorated and passed away at 20 days of age. High-resolution GTG-banded karyotype showed lack of centromeric constriction in some chromosomes, premature centromere separation in others, and repulsion of the heterochromatin regions. Molecular analysis of the ESCO2 gene revealed a deletion of 4 bp involving exon 4 in homozygosity (NM_00107420.2:c.875_878delACAG), which causes loss of ESCO2 function. We describe the clinical presentation caused by a rare ESCO2 variant.

Spontaneous intracranial hemorrhage and multiple intracranial aneurysms in a patient with Roberts/SC phocomelia syndrome

Roberts/SC phocomelia syndrome (RBS) is a rare but distinct genetic disorder with an autosomal recessive inheritance pattern. It has been associated with microcephaly, craniofacial malformation, cavernous hemangioma, encephalocele, and hydrocephalus. There are no previously reported cases of RBS with intracranial aneurysms. The authors report on a patient with a history of RBS who presented with a spontaneous posterior fossa hemorrhage. Multiple small intracranial aneurysms were noted on a preoperative CT angiogram. The patient underwent emergency craniotomy for evacuation of the hemorrhage. A postoperative angiogram confirmed the presence of multiple, distal small intracranial aneurysms.

Prenatal diagnosis of Roberts syndrome and detection of an ESCO2 frameshift mutation in a Pakistani family

OBJECTIVES

We report two siblings with Roberts syndrome (RBS), and an attempt to delineate the underlying molecular mechanism leading to familial recurrence.

METHODS

Cytogenetic studies and direct sequencing of the ESCO2 gene were carried out in the second affected fetus and the parents. Fetal DNA was obtained from amniocytes after amniocentesis. Parental DNA was obtained from peripheral blood samples.

RESULTS

Cytogenetic analysis of amniocytes revealed a normal male karyotype in 20 analyzed metaphases and chromosomal aneuploidies in 10 metaphases. All metaphases displayed premature separation of centromeres and puffing of heterochromatic regions near the centromere. A homozygous mutation leading to a frameshift in ESCO2 was identified in the fetal DNA sample. Both parents are heterozygous carriers of the same mutation.

CONCLUSION

The present case demonstrates the prenatal diagnosis of RBS associated with a frameshift mutation in ESCO2.

Roles of the sister chromatid cohesion apparatus in gene expression, development, and human syndromes

The sister chromatid cohesion apparatus mediates physical pairing of duplicated chromosomes. This pairing is essential for appropriate distribution of chromosomes into the daughter cells upon cell division. Recent evidence shows that the cohesion apparatus, which is a significant structural component of chromosomes during interphase, also affects gene expression and development. The Cornelia de Lange (CdLS) and Roberts/SC phocomelia (RBS/SC) genetic syndromes in humans are caused by mutations affecting components of the cohesion apparatus. Studies in Drosophila suggest that effects on gene expression are most likely responsible for developmental alterations in CdLS. Effects on chromatid cohesion are apparent in RBS/SC syndrome, but data from yeast and Drosophila point to the likelihood that changes in expression of genes located in heterochromatin could contribute to the developmental deficits.

Inactivating mutations in ESCO2 cause SC phocomelia and Roberts syndrome: no phenotype-genotype correlation

The rare, autosomal recessive Roberts syndrome (RBS) is characterized by tetraphocomelia, profound growth deficiency of prenatal onset, craniofacial anomalies, microcephaly, and mental deficiency. SC phocomelia (SC) has a milder phenotype, with a lesser degree of limb reduction and with survival to adulthood. Since heterochromatin repulsion (HR) is characteristic for both disorders and is not complemented in somatic-cell hybrids, it has been hypothesized that the disorders are allelic. Recently, mutations in ESCO2 (establishment of cohesion 1 homolog 2) on 8p21.1 have been reported in RBS. To determine whether ESCO2 mutations are also responsible for SC, we studied three families with SC and two families in which variable degrees of limb and craniofacial abnormalities, detected by fetal ultrasound, led to pregnancy terminations. All cases were positive for HR. We identified seven novel mutations in exons 3-8 of ESCO2. In two families, affected individuals were homozygous--for a 5-nucleotide deletion in one family and a splice-site mutation in the other. In three nonconsanguineous families, probands were compound heterozygous for a single-nucleotide insertion or deletion, a nonsense mutation, or a splice-site mutation. Abnormal splice products were characterized at the RNA level. Since only protein-truncating mutations were identified, regardless of clinical severity, we conclude that genotype does not predict phenotype. Having established that RBS and SC are caused by mutations in the same gene, we delineated the clinical phenotype of the tetraphocomelia spectrum that is associated with HR and ESCO2 mutations and differentiated it from other types of phocomelia that are negative for HR.

Mapping of a single locus capable of complementing the defective heterochromatin phenotype of Roberts syndrome cells

Roberts syndrome (RS) is a developmental disorder characterized by tetraphocomelia and a broad spectrum of additional clinical features. Most patients with RS exhibit characteristic cytogenetic phenotypes, which include an abnormal appearance of pericentromeric heterochromatin on metaphase chromosomes, referred to as "heterochromatic repulsion." In the present study, we use complementation of this abnormal cytogenetic phenotype as a means to identify a specific region of the normal human genome capable of rendering phenotypic correction. We screened the entire human genome, using a transient chromosome-transfer assay, and demonstrated complementation exclusively after the transfer of proximal chromosome 8p, a result subsequently confirmed by stable microcell-mediated chromosome transfer. Additionally, homozygosity mapping was used to refine the interval of this complementing locus to 8p21. The results are consistent with the notion that the single gene defect responsible for heterochromatic splaying and developmental abnormalities maps to chromosome 8p21.

Recapitulation of the Roberts syndrome cellular phenotype by inhibition of INCENP, ZWINT-1 and ZW10 genes

Roberts syndrome is an autosomal recessive disorder characterised primarily by symmetric reduction of all limbs and growth retardation. Patients have been reported to have premature separation of heterochromatin regions of many chromosomes and abnormalities in cell cycle. Given the rarity of the syndrome, the linkage analysis approach is not suitable to identify the responsible gene. In this work, a cell line derived from a patient affected by Roberts syndrome was characterized by cell biology and molecular cytogenetics, including comparative genomic hybridization and spectral karyotype. No recurrent chromosomal rearrangements were identified. Thereafter, based on the fact that premature chromatide separation is a reliable marker of the disease, we used antisense oligonucleotide technologies to inhibit six genes involved in various steps of the correct chromosome segregation, such as chromosome cohesion, kinetochore assembling, spindle checkpoint and spindle formation. We found that the inhibition of INCENP, ZWINT-1, ZW10 genes results in the appearance of mitotic cells characterised by centromere separation, chromosome aneuploidy and micronuclei formation. In addition, INCENP, ZWINT-1, ZW10 antisense-treated chromosome morphology was very similar to that of Roberts chromosome when analysed by atomic force microscopy. We concluded that INCENP, ZWINT-1, ZW10 gene inhibition results in cellular phenocopies of Roberts syndrome. Taken together, these findings support a possible role of these genes in the pathogenesis of Roberts syndrome.

Centromeres become unstuck without heterochromatin

In most if not all eukaryotes, sister-chromatid cohesion, which is mediated by the chromosomal complex Cohesin, is destroyed by proteolysis at the transition from metaphase to anaphase. In metazoans, Cohesin is removed from chromosomes in two steps, and the centromere and its associated pericentric heterochromatin constitute the last point of linkage between sister chromatids at metaphase. Mechanistic insight is now emerging on the way in which cells distinguish cohesion at the centromere from cohesion along chromosome arms. We discuss recent advances in our understanding of the role of centromeric heterochromatin in sister-chromatid cohesion and propose a causal relationship between this specialized type of chromatin and the removal by proteolysis of Cohesins that are associated with it.