Seher Basaran

The molecular mechanism underlying Roberts syndrome involves loss of ESCO2 acetyltransferase activity

Roberts syndrome/SC phocomelia (RBS) is an autosomal recessive disorder with growth retardation, craniofacial abnormalities and limb reduction. Cellular alterations in RBS include lack of cohesion at the heterochromatic regions around centromeres and the long arm of the Y chromosome, reduced growth capacity, and hypersensitivity to DNA damaging agents. RBS is caused by mutations in ESCO2, which encodes a protein belonging to the highly conserved Eco1/Ctf7 family of acetyltransferases that is involved in regulating sister chromatid cohesion. We identified 10 new mutations expanding the number to 26 known ESCO2 mutations. We observed that these mutations result in complete or partial loss of the acetyltransferase domain except for the only missense mutation that occurs in this domain (c.1615T>G, W539G). To investigate the mechanism underlying RBS, we analyzed ESCO2 mutations for their effect on enzymatic activity and cellular phenotype. We found that ESCO2 W539G results in loss of autoacetyltransferase activity. The cellular phenotype produced by this mutation causes cohesion defects, proliferation capacity reduction and mitomycin C sensitivity equivalent to those produced by frameshift and nonsense mutations associated with decreased levels of mRNA and absence of protein. We found decreased proliferation capacity in RBS cell lines associated with cell death, but not with increased cell cycle duration, which could be a factor in the development of phocomelia and cleft palate in RBS. In summary, we provide the first evidence that loss of acetyltransferase activity contributes to the pathogenesis of RBS, underscoring the essential role of the enzymatic activity of the Eco1p family of proteins.

Frequency of renal malformations in Turner syndrome: analysis of 82 Turkish children

Abstract We evaluated the frequency of renal malformations in relation to nonmosaic 45,X (group A, 45 patients, 54.9%) and mosaic/structural abnormalities of X (group B, 37 patients, 45.1%) in 82 Turkish patients with Turner syndrome (TS). Ultrasonography of the kidneys and collecting system was performed in all patients. Of the 82 patients, 31 had different renal malformations (37.8%). Horse-shoe kidney was observed in 9 (29.0%) of the 31 patients, and 17 patients (54.8%) had various collecting system malformations, while 5 (16.2%) had malrotation and other positional abnormalities. The prevalence of renal malformations was significantly higher in group A (51.1%) than group B (21.6%) (2:7.94, P<0.05). Although 8 of the 9 patients with horse-shoe kidney had the 45,X karyotype, collecting system malformations were observed more frequently in group B. Recurrent urinary tract infections (UTIs) were detected during follow-up in 7 patients, and hypertension developed in 3 patients. In patients who had a normal baseline nephrological evaluation, no problem suggesting renal disease developed during follow-up. We conclude that all forms of TS should have routine nephrological screening on diagnosis, since structural malformations of the kidney occur more frequently in nonmosaic 45,X TS, while collecting system malformations are mostly seen in mosaic/structural X forms. Those included in the group for nephrological follow-up had an increased risk for hypertension and/or UTI.

Dandy-Walker Malformation: A Review of 78 Cases Diagnosed by Prenatal Sonography

Objective: The purpose of this study was to determine the associated abnormalities and clinical outcomes of fetuses with Dandy-Walker malformations. Methods: Sonograms and medical reports of 78 cases were reviewed and information regarding each outcome was collected from autopsy records, hospital charts and specialists caring for the surviving infants. Results: We identified 64 fetuses with classic Dandy-Walker malformation (DW) and 14 fetuses with Dandy-Walker variant (DWV). A high proportion (44.8%) of the parents were consanguineous. The spectrum and proportion of central nervous system (67.1 vs. 71.4%; p = 1.0) and other malformations (43.7 vs. 64.2%; p = 0.57) associated with DW and DWV were similar. Chromosome abnormalities were found in 9 of the 51 (17.6%) fetuses that underwent karyotype analysis. Only 4 of 64 (6.2%) DW and 3 of 14 (21.4%) DWV infants survived (p 0.14), and all surviving infants with DW or DWV had neurological disorders. Conclusions: DW and DWV cases show so many similarities that a clear-cut distinction is difficult. There was no significant difference in the spectrum of associated anomalies and postnatal prognosis between DW and DWV cases.

MYO15A (DFNB3) mutations in Turkish hearing loss families and functional modeling of a novel motor domain mutation.

Myosin XVA is an unconventional myosin which has been implicated in autosomal recessive nonsyndromic hearing impairment (ARNSHI) in humans. In Myo15A mouse models, vestibular dysfunction accompanies the autosomal recessive hearing loss. Genomewide homozygosity mapping and subsequent fine mapping in two Turkish families with ARNSHI revealed significant linkage to a critical interval harboring a known deafness gene MYO15A on chromosome 17p13.1‐17q11.2. Subsequent sequencing of the MYO15A gene led to the identification of a novel missense mutation, c.5492G → T (p.Gly1831Val) and a novel splice site mutation, c.8968 − 1G → C. These mutations were not detected in additional 64 unrelated ARNSHI index patients and in 230 Turkish control chromosomes. Gly1831 is a conserved residue located in the motor domains of the different classes of myosins of different species. Molecular modeling of the motor head domain of the human myosin XVa protein suggests that the Gly1831Val mutation inhibits the powerstroke by reducing backbone flexibility and weakening the hydrophobic interactions necessary for signal transmission to the converter domain.

A new locus for autosomal recessive non‐syndromic mental retardation maps to 1p21.1–p13.3

Autosomal recessive inheritance of non‐syndromic mental retardation (ARNSMR) may account for approximately 25% of all patients with non‐specific mental retardation (NSMR). Although many X‐linked genes have been identified as a cause of NSMR, only three autosomal genes are known to cause ARNSMR. We present here a large consanguineous Turkish family with four mentally retarded individuals from different branches of the family. Clinical tests showed cognitive impairment but no neurological, skeletal, and biochemical involvements. Genome‐wide mapping using Human Mapping 10K Array showed a single positive locus with a parametric LOD score of 4.92 in a region on chromosome 1p21.1–p13.3. Further analyses using polymorphic microsatellite markers defined a 6.6‐Mb critical region containing approximately 130 known genes. This locus is the fourth one linked to ARNSMR.

Mild nasal malformations and parietal foramina caused by homozygous ALX4 mutations

We report on a boy born to consanguineous parents, who had hypertelorism, a broad nasal bridge, ridge and tip, bifid nasal tip, cleft alae nasi, broad columella, unilateral preauricular tag, shallow labiogingival sulcus, and bilateral large parietal foramina. Cranial MRI revealed a kinked corpus body and small cerebellar vermis. Molecular analysis uncovered a homozygous c.673C > G (p.Q225E) mutation in ALX4 gene. We compare the relatively mild phenotype in the patient to the more marked phenotype described in other patients with homozygous ALX4 mutations, and to the phenotypes in patients with mutations in other ALX genes.

Congenital heart disease in children with Down's syndrome: Turkish experience of 13 years.

Background — Down’s syndrome (DS) is the most common chromosomal abnormality due to a trisomy of chromosome 21 commonly associated with congenital heart defects (CHDs). This study aimed to evaluate the frequency and types of CHD patterns in Turkish children with DS. Method — The data relate to paediatric patients with DS who underwent cardiologic screening between 1994 and 2007 and were reviewed in our Paediatric Cardiology unit. Results — Four hundred and twenty-one out of the 1042 paediatric patients with DS studied over a 13-year period had associated CHD. Of these, 320 (77.6%) had a single cardiac lesion, while the remaining 92 patients (22.4%) had multiple defects. The most common single defect was an atrioventricular septal defect (AVSD) found in 141 patients (34.2%), followed by 69 patients (16.7%) showing secundum type atrial septal defect, and ventricular septal defect in 68 patients (16.5%). AVSDs were the leading type, isolated or combined with other cardiac anomalies with an overall occurrence of 19.8% of paediatric patients with DS, and 49.2% of paediatric patients with both DS and CHD. Conclusion — This is the first study concerning the frequency and type of CHD observed in Turkish children with DS.The high frequency of AVSD in Turkish children with DS implied that early screening for CHDs by echocardiography is crucial. The correction of AVSDs in paediatric patients with DS should be performed in the first 6 months of life to avoid irreversible haemodynamic consequences of the defect.

Prenatal diagnosis of 13q-syndrome in a fetus with dandy-walker malformation

BACKGROUND: Partial deletion of the long arm of the chromosome 13 is a rare chromosomal aberration and may present with microcephaly, colobomata, microphthalmia, distal limb and digital anomalies, cardiac defects, brain and urogenital malformations, anal atresia and growth restriction. CASE: We report such a case in 25th week of gestation referred for sonographic examination which revealed growth restriction, microcephaly, Dandy-Walker malformation, right microphthalmia, micrognathia, marked nuchal edema, four fingers–oligodactyly in feet and in hands with thumb aplasia and ambiguous genitalia. Chromosome analysis identified chromosome 13q deletion [46 XY del (13) (13q31.2/q32.1 → qter)]. Postmortem examination confirmed prenatal findings and showed aniridia, low-set ears, cryptorchidism, and anal atresia. CONCLUSION: Detection of Dandy-Walker malformation, microphthalmia, oligodactyly with thumb aplasia and growth restriction during prenatal ultrasonography should be a reminder of deletion of chromosome 13q and warrant cytogenetic analysis.

Molecular genetic screening of MBS1 locus on chromosome 13 for microdeletions and exclusion of FGF9, GSH1 and CDX2 as causative genes in patients with Moebius syndrome.

Moebius syndrome is a rare disorder primarily characterized by congenital facial palsy, frequently accompanied by ocular abduction anomalies, and occasionally associated with orofacial, limb and musculoskeletal malformations. Abnormal development of cranial nerves V through XII underlines the disease pathogenesis. Although some investigations suggested that a causative gene may lie on 13q12.2-q13, there have been no molecular studies targeting possible microdeletions in this region to date. In the present study, we performed microdeletion analyses on 13q12.11-q13 in nine patients, and sequenced three candidate genes in nineteen patients for functional relevance and further resolution of our screening. We ruled out microdeletions on the critical region as a common cause of Moebius syndrome and excluded FGF9, GSH1 and CDX2 genes.

Partial Molar Appearance of the Placenta in Trisomy 13

Although molecular studies have shown that more than 90% of partial moles are secondary to diandric triploidy, there are some rare cases with tetraploidy or unspecified aneuploidies. We diagnosed 3 cases of partial mole presentation during the 2nd trimester of pregnancy with multiple fetal abnormalities. In all 3 cases, cytogenetic studies showed trisomy 13. We present the cases and discuss the clinical and pathological aspects of the conditions presented as partial moles.