Faustina Lalatta

Cryptic deletions are a common finding in “balanced” reciprocal and complex chromosome rearrangements: a study of 59 patients

Using array comparative genome hybridisation (CGH) 41 de novo reciprocal translocations and 18 de novo complex chromosome rearrangements (CCRs) were screened. All cases had been interpreted as “balanced” by conventional cytogenetics. In all, 27 cases of reciprocal translocations were detected in patients with an abnormal phenotype, and after array CGH analysis, 11 were found to be unbalanced. Thus 40% (11 of 27) of patients with a “chromosomal phenotype” and an apparently balanced translocation were in fact unbalanced, and 18% (5 of 27) of the reciprocal translocations were instead complex rearrangements with >3 breakpoints. Fourteen fetuses with de novo, apparently balanced translocations, all but two with normal ultrasound findings, were also analysed and all were found to be normal using array CGH. Thirteen CCRs were detected in patients with abnormal phenotypes, two in women who had experienced repeated spontaneous abortions and three in fetuses. Sixteen patients were found to have unbalanced mutations, with up to 4 deletions. These results suggest that genome-wide array CGH may be advisable in all carriers of “balanced” CCRs. The parental origin of the deletions was investigated in 5 reciprocal translocations and 11 CCRs; all were found to be paternal. Using customised platforms in seven cases of CCRs, the deletion breakpoints were narrowed down to regions of a few hundred base pairs in length. No susceptibility motifs were associated with the imbalances. These results show that the phenotypic abnormalities of apparently balanced de novo CCRs are mainly due to cryptic deletions and that spermatogenesis is more prone to generate multiple chaotic chromosome imbalances and reciprocal translocations than oogenesis.

Hypomethylation at multiple maternally methylated imprinted regions including PLAGL1 and GNAS loci in Beckwith–Wiedemann syndrome

Genomic imprinting is an epigenetic phenomenon restricting gene expression in a manner dependent on parent of origin. Imprinted gene products are critical regulators of growth and development, and imprinting disorders are associated with both genetic and epigenetic mutations, including disruption of DNA methylation within the imprinting control regions (ICRs) of these genes. It was recently reported that some patients with imprinting disorders have a more generalised imprinting defect, with hypomethylation at a range of maternally methylated ICRs. We report a cohort of 149 patients with a clinical diagnosis of Beckwith–Wiedemann syndrome (BWS), including 81 with maternal hypomethylation of the KCNQ1OT1 ICR. Methylation analysis of 11 ICRs in these patients showed that hypomethylation affecting multiple imprinted loci was restricted to 17 patients with hypomethylation of the KCNQ1OT1 ICR, and involved only maternally methylated loci. Both partial and complete hypomethylation was demonstrated in these cases, suggesting a possible postzygotic origin of a mosaic imprinting error. Some ICRs, including the PLAGL1 and GNAS/NESPAS ICRs implicated in the aetiology of transient neonatal diabetes and pseudohypoparathyroidism type 1b, respectively, were more frequently affected than others. Although we did not find any evidence for mutation of the candidate gene DNMT3L, these results support the hypotheses that trans-acting factors affect the somatic maintenance of imprinting at multiple maternally methylated loci and that the clinical presentation of these complex cases may reflect the loci and tissues affected with the epigenetic abnormalities.

Seizure and EEG Patterns in Angelman's Syndrome

We studied the seizure and polygraphic patterns of 18 patients with Angelmans syndrome. All patients showed movement problems. Eleven patients were also reported to have long-lasting periods of jerky movements. The polygraphic recording showed a myoclonic status epilepticus in nine of them. Seven patients had partial seizures with eye deviation and vomiting, similar to those of childhood occipital epilepsies. These seizures and electroencephalographic patterns suggest that Angelmans syndrome occurs in most of the patients as a nonprogressive, age-dependent myoclonic encephalopathy with a prominent occipital involvement. These findings indicate that, whereas ataxia is a constant symptom in Angelmans syndrome, the occurrence of a transient myoclonic status epilepticus may account for the recurrence of different abnormal movements, namely the jerky ones. (J Child Neurol 1995;10:467-471).

Recurrent microdeletion at 17q12 as a cause of Mayer-Rokitansky-Kuster-Hauser (MRKH) syndrome: two case reports

BackgroundMayer-Rokitansky-Kuster-Hauser syndrome (MRKH) consists of congenital aplasia of the uterus and the upper part of vagina due to anomalous development of Müllerian ducts, either isolated or associated with other congenital malformations, including renal, skeletal, hearing and heart defects. This disorder has an incidence of approximately 1 in 4500 newborn girls and the aetiology is poorly understood.Methods and Resultswe report on two patients affected by MRKH syndrome in which array-CGH analysis disclosed an identical deletion spanning 1.5 Mb of genomic DNA at chromosome 17q12. One patient was affected by complete absence of uterus and vagina, with bilaterally normal ovaries, while the other displayed agenesis of the upper part of vagina, right unicornuate uterus, non cavitating rudimentary left horn and bilaterally multicystic kidneys. The deletion encompassed two candidate genes, TCF2 and LHX1. Mutational screening of these genes in a selected group of 20 MRKH females without 17q12 deletion was negative.ConclusionDeletion 17q12 is a rare albeit recurrent anomaly mediated by segmental duplications, previously reported in subjects with developmental kidney abnormalities and diabetes. The present two patients expand the clinical spectrum associated with this imbalance and suggest that this region is a candidate locus for a subset of MRKH syndrome individuals, with or without renal defects.

Banking together. A unified model of informed consent for biobanking

D uring the past 10 years, human biological material—body fluids, cells, tissues, intracellular substances or DNA—and the related data have become an important resource for academic medical research, and for the industrial development of diagnostics and therapeutics (Godard et al, 2003). The increasing creation and use of biobanks that store both the material and the related data bears witness to their scientific value, but there is still no consensus— either internationally, or at the European or national levels—about the regulations that should govern biobanks in ethical or legal terms (Cambon-Thomsen et al, 2007; Kaye, 2005). In particular, consent models designed to appropriately regulate biobankbased research are characterized by a maze of laws, policies and ethical recommendations that range from strict (specific informed consent) to basically unrestricted use (broad consent; Boggio et al, 2007).

De novo balanced chromosome rearrangements in prenatal diagnosis

We surveyed the datasheets of 29 laboratories concerning prenatal diagnosis of de novo apparently balanced chromosome rearrangements to assess the involvement of specific chromosomes, the breakpoints distribution and the impact on the pregnancy outcome.

FAM111A mutations result in hypoparathyroidism and impaired skeletal development

Kenny-Caffey syndrome (KCS) and the similar but more severe osteocraniostenosis (OCS) are genetic conditions characterized by impaired skeletal development with small and dense bones, short stature, and primary hypoparathyroidism with hypocalcemia. We studied five individuals with KCS and five with OCS and found that all of them had heterozygous mutations in FAM111A. One mutation was identified in four unrelated individuals with KCS, and another one was identified in two unrelated individuals with OCS; all occurred de novo. Thus, OCS and KCS are allelic disorders of different severity. FAM111A codes for a 611 amino acid protein with homology to trypsin-like peptidases. Although FAM111A has been found to bind to the large T-antigen of SV40 and restrict viral replication, its native function is unknown. Molecular modeling of FAM111A shows that residues affected by KCS and OCS mutations do not map close to the active site but are clustered on a segment of the protein and are at, or close to, its outer surface, suggesting that the pathogenesis involves the interaction with as yet unidentified partner proteins rather than impaired catalysis. FAM111A appears to be crucial to a pathway that governs parathyroid hormone production, calcium homeostasis, and skeletal development and growth.

Full COLD-PCR Protocol for Noninvasive Prenatal Diagnosis of Genetic Diseases

To the Editor: After the discovery of fetal DNA in maternal plasma, investigators reported different strategies for the noninvasive prenatal diagnosis of genetic diseases (1). Despite the advances in improving the analytical sensitivity of methods, distinguishing between fetal and maternal sequences remains very challenging, and the field of noninvasive prenatal diagnosis of genetic diseases has yet to attain a routine application in clinical diagnostics. An innovative strategy that has been reported is based on COLD-PCR (coamplification at a lower denaturation temperature PCR),1 which exploits melting temperature ( T m) differences between variant or mismatched sequences and wild-type sequences. This approach uses a critical denaturation temperature ( T c) lower than the T m to selectively amplify minority mutated alleles (2). We have developed assays for the identification of fetal paternally inherited mutations in maternal plasma. These assays use full COLD-PCR for the detection of IVSI.110 (G>A) and Cd39 (C>T) HBB (globin, beta) gene mutations that cause β-thalassemia. Full COLD-PCR is based on the generation of heteroduplexes between mutant and wild-type sequences. These heteroduplexes melt at lower temperatures than the wild-type homoduplexes. They are selectively denatured at the T c and then subsequently amplified. Given that both the fetal and maternal DNA content in maternal plasma has been demonstrated to vary from pregnancy to …

Recurrence of congenital heart disease in cases with familial risk screened prenatally by echocardiography.

Objectives. To evaluate the recurrence of congenital heart disease (CHD) in pregnant women with familial risk who had been referred for fetal echocardiography. Material and Methods. 1634 pregnancies from 1483 women with familial history of CHD in one or more relatives were studied. Fetal cardiologic diagnosis was compared with postnatal findings at 6 months or at autopsy. Results. Total recurrence rate of CHD was 3.98%, 4.06% in single familial risk, 2.9% in double, and 5% in multiple risk. It was 3.5% in case of one previously affected child; 4.5% with 2 children; 5.2% with the mother alone affected and 7,5% with father alone affected and 3.5% with a single distant relative. Exact concordance of CHD was found in 21.5% and a partial concordance in 20% of cases. Conclusions. Our data show a higher recurrence rate of CHD than previously published data and high relative risk ratios compared to normal population.

High phenotypic intrafamilial variability in patients with Pendred syndrome and a novel duplication in the SLC26A4 gene: clinical characterization and functional studies of the mutated SLC26A4 protein

OBJECTIVE Pendred syndrome (PS) is characterized by the association of sensorineural hearing loss (SNHL) and a partial iodide organification defect at the thyroid level. It is caused by mutations in the SLC26A4 gene. The encoded transmembrane protein, called pendrin, has been found to be able to transport chloride and other anions. DESIGN The aim of the present study was to characterize a family with PS, which shows a strong intrafamilial phenotypic variability, including kidney atrophy in one member. The age of disease-onset was significantly different in all three affected siblings, ranging from 2 to 21 years for thyroid alterations and from 1.5 to 11 years for SNHL. METHODS Clinical and genetic studies were carried out in affected siblings. The functional activity of the novel duplication found was studied by a fluorimetric method in a human renal cell line (HEK293 Phoenix) in which the protein was overexpressed. RESULTS All three siblings were found to be compound heterozygotes for the missense mutation (1226G>A, R409H) and for a novel 11 bp duplication (1561_1571CTTGGAATGGC, S523fsX548). The latter mutation creates a frame shift leading to the loss of the entire carboxy-terminus domain. Functional studies of this mutant demonstrated impaired transport of chloride and iodide when expressed in HEK 293 Phoenix cells, when compared with wild type pendrin. CONCLUSIONS A novel 11 bp duplication was found in a family with Pendred syndrome, showing a high intrafamilial phenotypic variability. An impaired transmembrane anionic transport of the mutated SLC26A4 protein was demonstrated in functional studies using a heterologous cell system.