Complex chromosome rearrangement in a child with microcephaly, dysmorphic facial features and mosaicism for a terminal deletion del(18)(q21.32-qter) investigated by FISH and array-CGH: Case report

We report on a 7 years and 4 months old Greek boy with mild microcephaly and dysmorphic facial features. He was a sociable child with maxillary hypoplasia, epicanthal folds, upslanting palpebral fissures with long eyelashes, and hypertelorism. His ears were prominent and dysmorphic, he had a long philtrum and a high arched palate. His weight was 17 kg (25th percentile) and his height 120 cm (50th percentile). High resolution chromosome analysis identified in 50% of the cells a normal male karyotype, and in 50% of the cells one chromosome 18 showed a terminal deletion from 18q21.32. Molecular cytogenetic investigation confirmed a del(18)(q21.32-qter) in the one chromosome 18, but furthermore revealed the presence of a duplication in q21.2 in the other chromosome 18. The case is discussed concerning comparable previously reported cases and the possible mechanisms of formation

Combined 22q11.1-q11.21 deletion with 15q11.2-q13.3 duplication identified by array-CGH in a 6 years old boy

<p>Abstract</p> <p>Background</p> <p>Deletions of chromosome 22q11 are present in over 90% of cases of DiGeorge or Velo-Cardio-Facial syndrome (DGS/VCFS). 15q11-q13 duplication is another recognized syndrome due to rearrangements of several genes, belonging to the category of imprinted genes. The phenotype of this syndrome varies but has been clearly associated with developmental delay and autistic spectrum disorders. Co-existence of the two syndromes has not been reported so far.</p> <p>Results</p> <p>Here we report a 6-year-old boy presenting growth retardation, dysmorphic features and who exhibited learning difficulties. Fluorescence in situ hybridization (FISH) analysis of the proband revealed a deletion of DiGeorge Syndrome critical region (TUPLE). Array-CGH analysis revealed an interstitial duplication of 12 Mb in size in the area 15q11.2-q13.3, combined with a 3.2 Mb deletion at region 22q11.1-q11.21. FISH analysis in the mother showed a cryptic balanced translocation between chromosome 15 and chromosome 22 (not evident by classic karyotyping).</p> <p>Discusion</p> <p>The clinical manifestations could be related to both syndromes and the importance of array-CGH analysis in cases of unexplained developmental delay is emphasized. The present case further demonstrates how molecular cytogenetic techniques applied in the parents were necessary for the genetic counseling of the family.</p

Primary open angle glaucoma due to T377M MYOC: Population mapping of a Greek founder mutation in Northwestern Greece

BACKGROUND: Mutations in the MYOC gene have been shown to explain 5% of unrelated primary open angle glaucoma (POAG) in different populations. In particular, the T377M MYOC mutation has arisen at least three separate times in history, in Great Britain, India, and Greece. The purpose of this study is to investigate the distribution of the mutation among different population groups in the northwestern region of Greece. MATERIALS AND METHODS: We explored the distribution of the "Greek" T377M founder mutation in the Epirus region in Northwestern Greece, which could be its origin. Genotyping was performed in POAG cases and controls by PCR amplification of the MYOC gene, followed by digestion with restriction enzyme. Statistical analyses were performed by an exact test, the Kaplan-Meier method and the t-test. RESULTS: In the isolated Chrysovitsa village in the Pindus Mountains, a large POAG family demonstrated the T377M mutation in 20 of 66 family members while no controls from the Epirus region (n = 124) carried this mutation (P < 0.001). Among other POAG cases from Epirus, 2 out of 14 familial cases and 1 out of 80 sporadic cases showed the mutation (P = 0.057). The probability of POAG diagnosis with advancing age among mutation carriers was 23% at age 40, and reached 100% at age 75. POAG patients with the T377M mutation were diagnosed at a mean age of 51 years (SD +/- 13.9), which is younger than the sporadic or familial POAG cases: 63.1 (SD +/- 11) and 66.8 (SD +/- 9.8) years, respectively. CONCLUSIONS: The T377M mutation was found in high proportion in members of the Chrysovitsa family (30.3%), in lower proportion in familial POAG cases (14.2%) and seems rare in sporadic POAG cases (1.2%), while no controls (0%) from the Epirus region carried the mutation. Historical and geographical data may explain the distribution of this mutation within Greece and worldwide

Multiple enhancers located in a 1-Mb region upstream of POU3F4 promote expression during inner ear development and may be required for hearing

POU3F4 encodes a POU-domain transcription factor required for inner ear development. Defects in POU3F4 function are associated with X-linked deafness type 3 (DFN3). Multiple deletions affecting up to ~900-kb upstream of POU3F4 are found in DFN3 patients, suggesting the presence of essential POU3F4 enhancers in this region. Recently, an inner ear enhancer was reported that is absent in most DFN3 patients with upstream deletions. However, two indications suggest that additional enhancers in the POU3F4 upstream region are required for POU3F4 function during inner ear development. First, there is at least one DFN3 deletion that does not eliminate the reported enhancer. Second, the expression pattern driven by this enhancer does not fully recapitulate Pou3f4 expression in the inner ear. Here, we screened a 1-Mb region upstream of the POU3F4 gene for additional cis-regulatory elements and searched for novel DFN3 mutations in the identified POU3F4 enhancers. We found several novel enhancers for otic vesicle expression. Some of these also drive expression in kidney, pancreas and brain, tissues that are known to express Pou3f4. In addition, we report a new and smallest deletion identified so far in a DFN3 family which eliminates 3.9 kb, comprising almost exclusively the previous reported inner ear enhancer. We suggest that multiple enhancers control the expression of Pou3f4 in the inner ear and these may contribute to the phenotype observed in DFN3 patients. In addition, the novel deletion demonstrates that the previous reported enhancer, although not sufficient, is essential for POU3F4 function during inner ear development

The contribution of the mitochondrial DNA mutations in non-syndromic, sensorineural greek deafness patients of childhood onset

Clinically significant hearing loss is present in at least 1.9 per 1,000 infants at birth and the prevalence rises to at least 2.7 per 1,000 by the age of four. Genetic causes of hearing loss are estimated to account for 68% of cases expressed at birth and 55% of those expressed by the age of four. Genetic deafness is divided into syndromic forms, in which hearing loss is associated with a variety of other anomalies, and non-syndromic forms. The syndromic forms account for 30% of prelingual genetic deafness and include several hundred deafness syndromes, with the underlying genetic defect being found in about 30 of them. In non-syndromic genetic deafness of prelingual onset, autosomal recessive inheritance predominates (80%), but autosomal dominant (20%), X-linked (1%), and mitochondrial (<1%) forms have also been described. Hearing loss can also be nongenetic in origin, induced by factors such as ototoxic drugs, perinatal infections, traumas etc. However, many cases are multifactorial, involving a collaboration of exogenous factors and mutations in single genes or several genes. The severity of hearing loss may range from mild to profound and the damage in hearing may include all frequencies. Mitochondrion harbors its own DNA, encoding certain essential components of the mitochondrial respiratory chain and protein synthesis apparatus. Mitochondrial DNA is transmitted only through the matrilineal lineage. Mitochondrial mutations are collected in the human mitochondrial genome database MITOMAP. Mitochondrial DNA mutations can be divided into large rearrangements and mutations limited to a few basepairs, the majority being point mutations. Most mitochondrial DNA deletions, duplications, insertions, inversions, or other complex rearrangements involve several genes, as mitochondrial genes are located close to each other. Large deletions generally remove at least one tRNA gene and are therefore likely to cause a translational defect and dysfunction of multiple components of oxidative phosphorylation, and consequently the whole energy process. Remarkably, specific mutations in tRNA genes can also lead to non-syndromic deafness, whereas other organ systems remain unaffected. This illustrates the limited genotype-phenotype correlation in mitochondrial disease. Mitochondrial DNA mutations have an impact on cellular ATP production and many of them are undoubtedly a factor that contributes to sensorineural deafness, including both syndromic and non-syndromic forms. Hot spot regions for deafness mutations are the MTRNR1 gene, encoding the 12S rRNA, the MTTS1 gene, encoding the tRNA for Ser(UCN), and the MTTL1 gene, encoding the tRNA for Leu(UUR). In the Caucasian population, at least 5% of postlingual, non-syndromic hearing impairment is due to known mitochondrial DNA mutations, thus representing the most frequent cause of hearing loss after the 35delG mutation in the GJB2 gene encoding connexin 26. In oriental populations the frequency might be even higher. However, it is unclear which percentage of postlingual hearing loss is due to mitochondrial DNA mutations, as these mutations might be both constitutional but also acquired (somatic). We investigated the impact of mitochondrial DNA mutations in the Greek hearing impaired population, by testing a cohort of 478 patients suffering from childhood onset prelingual or postlingual, bilateral, sensorineural, non-syndromic hearing loss of any degree for six mitochondrial variants previously associated with deafness. Screening involved the MTRNR1 961delT/insC and A1555G mutations, the MTTL1 A3243G mutation, and the MTTS1 A7445G, 7472insC and T7510C mutations. Although two patients were tested positive for the A1555G mutation, we failed to identify any subject carrying the 961delT/insC, A3243G, A7445G, 7472insC, or T7510C mutations. Our findings strongly suggest that mitochondrial DNA mutations are not a major risk factor for sensorineural deafness in the Greek population and they further support the general notion that mitochondrial DNA mutations are responsible for <1% of deafness cases.Η κλινικά σημαντική απώλεια ακοής εμφανίζεται με συχνότητα 1,9 σε 1.000 νεογνά στη γέννηση, ενώ η συχνότητα αυξάνει σε 2,7 άτομα στα 1.000 στην ηλικία των τεσσάρων ετών. Οι γενετικές αιτίες της απώλειας ακοής υπολογίζεται ότι αφορούν το 68% των περιπτώσεων βαρηκοΐας στη γέννηση και το 55% των περιπτώσεων βαρηκοΐας στα τέσσερα έτη. Η βαρηκοΐα γενετικού τύπου διαχωρίζεται σε συνδρομικές μορφές, στις οποίες η απώλεια ακοής συνοδεύεται από τουλάχιστον ένα κλινικό σύμπτωμα και σε μη συνδρομικές μορφές. Οι συνδρομικές μορφές απαντώνται στο 30% της προγλωσσικής βαρηκοΐας ενώ από τα αρκετές εκατοντάδες σύνδρομα μόλις σε 30 από αυτά έχει βρεθεί η γενετική βλάβη που τα προκαλεί. Στη μη συνδρομική, προγλωσσική βαρηκοΐα, η αυτοσωματική υπολειπόμενη κληρονομικότητα είναι η πιο συχνή (80%), έπεται η αυτοσωματική επικρατής (20%), ενώ η φυλοσύνδετη (1%) και η μιτοχονδριακή (<1%) βαρηκοΐα αποτελούν σπανιότερες μορφές. Η απώλεια ακοής μπορεί επίσης να μην είναι γενετικής αιτιολογίας και να οφείλεται σε παράγοντες όπως είναι τα ωτοτοξικά φάρμακα, οι περιγεννητικές λοιμώξεις, τραύματα, κλπ. Επίσης, πολλές περιπτώσεις είναι πολυπαραγοντικές και περιλαμβάνουν μία συνεργασία εξωγενών παραγόντων και μεταλλαγών σε ένα ή περισσότερα γονίδια. Η βαρύτητα της απώλειας ακοής μπορεί να εκτείνεται από ήπια βαρηκοΐα έως και κώφωση ενώ η βλάβη στην ακοή μπορεί να περιλαμβάνει όλες τις συχνότητες. Το μιτοχόνδριο έχει το δικό του DNA, το οποίο κωδικοποιεί για συγκεκριμένους παράγοντες που είναι απαραίτητοι για τη μιτοχονδριακή αναπνευστική αλυσίδα και την πρωτεϊνοσύνθεση. Το μιτοχονδριακό DNA κληρονομείται αποκλειστικά και μόνο μέσω της μητρικής γενεαλογικής γραμμής. Οι μιτοχονδριακές μεταλλαγές συλλέγονται στη βάση δεδομένων του ανθρώπινου μιτοχονδριακού γονιδιώματος MITOMAP. Οι μεταλλαγές του μιτοχονδριακού DNA μπορεί να περιλαμβάνουν είτε μεγάλες ανακατατάξεις, είτε μικρές αλλαγές λίγων βάσεων από τις οποίες η πλειοψηφία είναι σημειακές μεταλλαγές. Οι περισσότερες ελλείψεις, διπλασιασμοί, αναστροφές ή άλλες σύνθετες ανακατατάξεις περιλαμβάνουν αρκετά μιτοχονδριακά γονίδια λόγω του ότι τα μιτοχονδριακά γονίδια βρίσκονται πολύ κοντά μεταξύ τους. Οι μεγάλες ελλείψεις γενικά αφαιρούν τουλάχιστον ένα tRNA γονίδιο με αποτέλεσμα να προκαλούν βλάβες στη μετάφραση και δυσλειτουργία σε πολλά σημεία της οξειδωτικής φωσφορυλίωσης και συνεπώς στη διαδικασία παραγωγής ενέργειας. Αξιοσημείωτο είναι ότι συγκεκριμένες μεταλλαγές στα tRNA γονίδια συχνά προκαλούν μη συνδρομική βαρηκοΐα, αφήνοντας τα άλλα όργανα ανέπαφα, γενονός που αποδεικνύει ότι ο συσχετισμός γονοτύπου– φαινοτύπου στα μιτοχονδριακά νοσήματα είναι περιορισμένος. Οι μεταλλαγές του μιτοχονδριακού DNA έχουν επίδραση στη παραγωγή ενέργειας στο κύτταρο με τη μορφή ΑΤΡ και πολλές από αυτές αποτελούν αναμφίβολα παράγοντα που συμβάλλει στη νευροαισθητήρια συνδρομική και μη συνδρομική βαρηκοΐα. Τα ‘θερμά σημεία’ για μεταλλαγές βαρηκοΐας είναι το γονίδιο MTRNR1 που κωδικοποιεί το 12S rRNA, το γονίδιο MTTS1 που κωδικοποιεί το tRNA για το Ser(UCN) και το γονίδιο MTTL1 που κωδικοποιεί το tRNA για το Leu(UUR). Στους Καυκάσιους πληθυσμούς, τουλάχιστον το 5% της προγλωσσικής, μη συνδρομικής απώλειας ακοής οφείλεται σε γνωστές μιτοχονδριακές μεταλλαγές, εκπροσωπώντας έτσι την πιο συχνή αιτία βαρηκοΐας μετά τη μεταλλαγή 35delG του πυρηνικού γονιδίου GJB2 που κωδικοποιεί για την πρωτεΐνη συνδετίνη 26. Στους Ασιατικούς πληθυσμούς αναμένεται η συχνότητα αυτή να είναι ακόμα μεγαλύτερη. Πάντως δεν είναι ξεκάθαρο ποιό ποσοστό της μεταγλωσσικής απώλειας ακοής οφείλεται σε μιτοχονδριακές μεταλλαγές μπορεί να είναι δομικές ή επίκτητες (σωματικές). Στην παρούσα μελέτη διερευνήθηκε η συμβολή των μεταλλαγών του μιτοχονδριακού DNA στον Ελληνικό πάσχοντα πληθυσμό. Εξετάστηκαν 478 ασθενείς με προγλωσσική ή μεταγλωσσική, αμφοτερόπλευρη, νευροαισθητήρια, μη συνδρομική βαρηκοΐα ανεξαρτήτως βαθμού για έξι μιτοχονδριακές μεταλλαγές οι οποίες έχουν σχετισθεί με τη νόσο. Στον μοριακό έλεγχο συμπεριλήφθησαν οι μεταλλαγές 961delT/insC και A1555G του γονιδίου MTRNR1, η μεταλλαγή A3243G του γονιδίου MTTL1 και οι μεταλλαγές A7445G, 7472insC και T7510C του γονιδίου MTTS1. Αν και δύο από τους ασθενείς βρέθηκαν θετικοί για τη μεταλλαγή A1555G, κανείς δε βρέθηκε να φέρει κάποια από τις μεταλλαγές 961delT/insC, A3243G, A7445G, 7472insC, ή T7510C. Τα ευρήματά μας αποδεικνύουν ότι οι μεταλλαγές του μιτοχονδριακού DNA δεν αποτελούν παράγοντα κινδύνου βαρηκοΐας στον Ελληνικό πληθυσμό και επιπλέον ενισχύουν τη γενική αντίληψη ότι οι μιτοχονδριακές μεταλλαγές ευθύνονται για λιγότερο από 1% των περιπτώσεων βαρηκοΐας

Investigating the impact of the Down syndrome related common MTHFR 677C &gt; T polymorphism in the Danish population

Chromosomal aneuploidy consists the leading cause of fetal death in our species. Around 50% of spontaneous abortions until 15 weeks of gestational age are chromosomally aneuploid, with trisomies accounting for 50% of the abnormal abortions. Trisomy 21 is the most common chromosome abnormality in liveborns and is usually the result of nondisjunction of chromosome 21 in meiosis in either oogenesis or spermatogenesis. To investigate the relationship between folate metabolism and Down syndrome (DS) in a Danish population, we analyzed the common 677C&gt;T genetic polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene. Our cohort consisted of 181 mothers of children with DS versus 1,084 healthy controls. Polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) were used to examine the MTHFR 677C&gt;T polymorphism. No significant association between the polymorphism and the risk for DS was found. We conclude that the common MTHFR 677C&gt;T polymorphism is not likely to be a maternal risk factor for DS in our cohort and that the difference to previous studies can probably be explained by small sample size or geographic variation in gene polymorphisms involving gene-nutritional or gene-gene or gene-nutritional-environmental factors

Easy, Rapid, and Cost-Effective Methods for Identifying Carriers of Recurrent GJB2 Mutations Causing Nonsyndromic Hearing Impairment in the Greek Population

A variety of techniques have been developed for screening the GJB2 gene for known and unknown mutations, especially the most common mutation in the Caucasian population, the c. 35delG. Other mutations that have been so far characterized in the GJB2 gene seem to have different geographical distributions, and therefore there is an interest in identifying recurrent mutations specific for each population and developing easy and rapid screening techniques. Here we present easy screening protocols for already identified recurrent mutations in the Greek population. Developing easy, rapid, and cost-effective screening methods will facilitate the detection of GJB2 recurrent mutation carriers, at large, in the Greek population

Hypothesizing an Ancient Greek Origin of the GJB2 35delG Mutation: Can Science Meet History?

One specific mutation of the GJB2 gene that encodes the connexin 26 protein, the 35delG mutation, has become a major interest among scientists who focus on the genetics of nonsyndromic hearing loss. The mutation accounts for the majority of GJB2 mutations detected in Caucasian populations and represents one of the most frequent disease mutations identified so far. The debate was so far between the arguments whether or not the 35delG mutation constitutes a mutational hot-spot or a founder effect; however, it was recently clarified that the latter seems the most likely. In an attempt to explore the origin and propagation of the 35delG mutation, several groups have reported the prevalence of the mutation and the carrier rates in different populations worldwide. It is now certain that the theory of a common founder prevails and that the highest carrier frequencies of the 35delG mutation are observed in southern European populations, giving rise to a discussion regarding the origin of the 35delG mutation. In this study, we discuss data previously published by our and other groups and also compare the haplotype distribution of the mutation in southern Europe, trying to understand the pathways of science and history and the conflict between them

Detection of Deafness-Causing Mutations in the Greek Mitochondrial Genome

Mitochondrion harbors its own DNA, known as mtDNA, encoding certain essential components of the mitochondrial respiratory chain and protein synthesis apparatus. mtDNA mutations have an impact on cellular ATP production and many of them are undoubtedly a factor that contributes to sensorineural deafness, including both syndromic and non-syndromic forms. Hot spot regions for deafness mutations are the MTRNR1 gene, encoding the 12S rRNA, the MTTS1 gene, encoding the tRNA for Ser(UCN), and the MTTL1 gene, encoding the tRNA for Leu(UUR). We investigated the impact of mtDNA mutations in the Greek hearing impaired population, by testing a cohort of 513 patients suffering from childhood onset prelingual or postlingual, bilateral, sensorineural, syndromic or non-syndromic hearing loss of any degree for six mitochondrial variants previously associated with deafness. Screening involved the MTRNR1 961delT/insC and A1555G mutations, the MTTL1 A3243G mutation, and the MTTS1 A7445G, 7472insC and T7510C mutations. Although two patients were tested positive for the A1555G mutation, we failed to identify any subject carrying the 961delT/insC, A3243G, A7445G, 7472insC, or T7510C mutations. Our findings strongly support our previously raised conclusion that mtDNA mutations are not a major risk factor for sensorineural deafness in the Greek population