Angela Ragusa

Heterozygous submicroscopic inversions involving olfactory receptor-gene clusters mediate the recurrent t(4;8)(p16;p23) translocation.

The t(4;8)(p16;p23) translocation, in either the balanced form or the unbalanced form, has been reported several times. Taking into consideration the fact that this translocation may be undetected in routine cytogenetics, we find that it may be the most frequent translocation after t(11q;22q), which is the most common reciprocal translocation in humans. Case subjects with der(4) have the Wolf-Hirschhorn syndrome, whereas case subjects with der(8) show a milder spectrum of dysmorphic features. Two pairs of the many olfactory receptor (OR)-gene clusters are located close to each other, on both 4p16 and 8p23. Previously, we demonstrated that an inversion polymorphism of the OR region at 8p23 plays a crucial role in the generation of chromosomal imbalances through unusual meiotic exchanges. These findings prompted us to investigate whether OR-related inversion polymorphisms at 4p16 and 8p23 might also be involved in the origin of the t(4;8)(p16;p23) translocation. In seven case subjects (five of whom both represented de novo cases and were of maternal origin), including individuals with unbalanced and balanced translocations, we demonstrated that the breakpoints fell within the 4p and 8p OR-gene clusters. FISH experiments with appropriate bacterial-artificial-chromosome probes detected heterozygous submicroscopic inversions of both 4p and 8p regions in all the five mothers of the de novo case subjects. Heterozygous inversions on 4p16 and 8p23 were detected in 12.5% and 26% of control subjects, respectively, whereas 2.5% of them were scored as doubly heterozygous. These novel data emphasize the importance of segmental duplications and large-scale genomic polymorphisms in the evolution and pathology of the human genome.

Inter-ethnic polymorphism of the β-globin gene locus control region (LCR) in sickle-cell anemia patients

Sequence polymorphisms within the 5′HS2 segment of human locus control region is described among sickle cell anemia patients. Distinct polymorphic patterns of a simple sequence repeat are observed in strong linkage disequilibrium with each of the five major βS haplotypes. Potential functional relevance of this polymorphic region in globin gene expression is discussed.

Celiac disease in Down's syndrome with HLA serological and molecular studies

The association between Downs syndrome (DS) and celiac disease (CD) has been confirmed by several authors. The sensitivity and specificity of antigliadin antibodies (AGAs), the clinical features of subjects with DS and CD (DS-CD+), the incidence of CD, and the results of serological and molecular class I and II HLA typing were determined in a sample of 57 Sicilian subjects with DS. Six (10.5%) and 17 subjects (29.8%) showed high levels of IgA AGAs and IgG AGAs, respectively. AGAs sensitivity and specificity were lower than in the population without DS. Ten people with DS were submitted to jejunal biopsy, and seven (12.2%) showed CD according to ESPGAN criteria. All seven patients were put on gluten-free diet, followed by rapid disappearance of symptoms. Class I and II HLA serological and molecular typing was carried out in seven DS-CD + subjects, 22 people with DS without CD (DS-CD-), five subjects with CD without DS, and 20 controls. Between DS-CD + and DS-CD- subjects, no statistically significant difference regarding serum HLA class I antigens was found. DQA1*0101 allele appears significantly in DS-CD + patients and deserves to be searched for in a larger sample to assess its meaning in the DS-CD association.

Evaluation of a mutation screening strategy for sporadic cases of ATR-X syndrome

We report on the evaluation of a strategy for screening for XNP/ATR-X mutations in males with mental retardation and associated dysmorphology. Because nearly half of the mutations in this gene reported to date fall into a short 300 bp region of the transcript, we decided to focus in this region and to extend the mutation analysis to cases with a negative family history. This study includes 21 mentally retarded male patients selected because they had severe mental retardation and a typical facial appearance. The presence of haemoglobin H or urogenital abnormalities was not considered critical for inclusion in this study. We have identified six mutations which represents a mutation detection rate of 28%. This figure is high enough for us to propose this strategy as a valid first level of screening in a selected subset of males with mental retardation. This approach is simple, does not require RNA preparation, does not involve time consuming mutation detection methods, and can thus be applied to a large number of patients at a low cost in any given laboratory.

Molecular basis of α-thalassemia in Sicily

Abstract To evaluate the allelic frequency and genetic diversity of α-thalassemia defects in Sicily, both epidemiological and patient-oriented studies were carried out. For the epidemiological study, phenotypic data were collected on more than 1000 Sicilian individuals. Among them, 427 were explored at the molecular level for nine α-thalassemic variants known to be common in the Mediterranean region. Our data reveal an allele frequency of 4.1% for α+-thalassemia matching that of β-thalassemia in this region. The presence of α°-thalassemia (––MEDI and ––CAL) was observed only in the group of referred patients. Newly acquired nucleotide sequence data on the deletional breakpoint of ––CAL allowed us to design a simple PCR-based procedure for exploring this allele. The data also provide additional information concerning the genetic mechanisms involved in such large deletions.

How microsatellite analysis can be exploited for subtelomeric chromosomal rearrangement analysis in mental retardation

Editor—The genetic causes of mental retardation are still largely unknown so that about 34% of cases of severe to moderate and 80% of mild mental retardation remain unresolved.1 ,2 Consequently, genetic counselling is difficult in these cases. Chromosomal rearrangements are still the most frequent cause of mental retardation and cytogenetic analysis at 400-550 band resolution cannot detect rearrangements smaller than 5 Mb. Therefore, any new technologies to improve cytogenetic analysis would be of great benefit. In recent years, there has been evidence that the cause of 6-7% of mental retardation involves subtle chromosome rearrangements. Several molecular methodologies have been used successfully to investigate the integrity of telomeres, such as hypervariable polymorphisms (HVPs), FISH, and CGH, while others based on DNA array approaches are being developed.2 The choice of method rests on considerations of feasibility, cost, reproducibility, and sensitivity. FISH and microsatellite analyses are the techniques most commonly used by numerous laboratories and both of them are still being evaluated in terms of their performance and practicability. FISH based analysis with telomeric specific probes provides a simultaneous investigation of all chromosomes ends, resulting in total detection of chromosome rearrangements without requiring the examination of parental chromosomes.3-5 However, this method does not assign parental origin, it loses UPD events, and only gives information regarding abnormalities spanning the probes DNA region. Although now simplified by being available in kit form, the method not only requires considerable expertise in molecular cytogenetics, but is also expensive and time consuming. HVP analysis using microsatellites, which is both easy and inexpensive, has two main problems, as it requires both parental DNA samples and high informativeness, established by the number and frequencies of alleles. However, even for highly heterozygous loci ≅0.8, the detection rate for monosomy and trisomy is 0.64 and 0.5, …

Screening of subtelomeric rearrangements in autistic disorder: Identification of a partial trisomy of 13q34 in a patient bearing a 13q;21p translocation

Within the framework of a FISH screening protocol to detect cryptic subtelomeric rearrangements in autistic disorder (AD), a patient bearing three copies of the subtelomeric portion of the q arm of chromosome 13 has been identified. Beside AD, the patient also has severe mental retardation and displays several dysmorphic features. Further FISH analyses revealed that the trisomy was caused by the translocation of a 13q subtelomeric fragment to the acrocentric tip of one chromosome 21 [46,XY.ish der(21) t(13;21) (q34;p13)(D13S1825+)]. Gene dosage experiments carried out with three multiallelic polymorphisms of the subtelomeric region of chromosome 13q showed that the putative length of the triplicate region does not exceed 300 kb about, that is, the distance from telomere to the first normally inherited marker. In addition, gene dosage analysis performed on the derivative chromosome 21, did not reveal loss of the most telomeric protein‐encoding genes on 21p. The potential relationship between a postulated increased expression of genes on 13q34 and the complex phenotype in this trisomic patient is discussed.

Decreased expression of GRAF1/OPHN-1-L in the X-linked alpha thalassemia mental retardation syndrome

BackgroundATRX is a severe X-linked disorder characterized by mental retardation, facial dysmorphism, urogenital abnormalities and alpha-thalassemia. The disease is caused by mutations in ATRX gene, which encodes a protein belonging to the SWI/SNF DNA helicase family, a group of proteins involved in the regulation of gene transcription at the chromatin level. In order to identify specific genes involved in the pathogenesis of the disease, we compared, by cDNA microarray, the expression levels of approximately 8500 transcripts between ATRX and normal males of comparable age.MethodscDNA microarray was performed using total RNA from peripheral blood mononuclear cells of ATRX and normal males. Microarray results were validated by quantitative real-time polymerase chain reaction.ResultscDNA microarray analysis showed that 35 genes had a lower expression (30-35% of controls) while 25 transcripts had a two-fold higher expression in comparison to controls. In the microarray results the probe for oligophrenin-1, a gene known for its involvement in mental retardation, showed a decreased hybridization signal. However, such gene was poorly expressed in blood mononuclear cells and its decrease was not confirmed in the quantitative real-time RT-PCR assay. On the other hand, the expression of an homologous gene, the GTPase regulator associated with the focal adhesion kinase 1/Oligophrenin-1-like (GRAF1/OPHN-1-L), was relatively high in blood mononuclear cells and significantly decreased in ATRX patients. The analysis of the expression pattern of the GRAF1/OPHN-1-L gene in human tissues and organs revealed the predominant brain expression of a novel splicing isoform, called variant-3.ConclusionsOur data support the hypothesis of a primary role for altered gene expression in ATRX syndrome and suggest that the GRAF1/OPHN-1-L gene might be involved in the pathogenesis of the mental retardation. Moreover a novel alternative splicing transcript of such gene, predominantly expressed in brain tissues, was identified.

Medial telangiectatic sacral nevi (types A and C) associated with Williams syndrome

Williams syndrome (WS) is an autosomal dominant condition characterized by a distinctive ‘elfin-like’ facial appearance (fig. 1), cardiac defects, mental retardation with outgoing personality and sometimes infantile hypocalcemia. Mutations in the elastin gene [1] are responsible, at least in part, for the disorder. Another gene involved in its pathogenesis is that for LIM kinase 1. Haploinsufficiency of the RFC2 gene has also been postulated as a factor. Furthermore, hemizygosity for the LIMK1 gene has been proposed as the basis for impaired visuospatial constructive cognition in this disorder. Many reports have detailed the most common manifestations of this syndrome [2]. We report here the association of WS with a cutaneous sign, medial telangiectatic sacral nevi (MTSN), which has never been described previously. We have evaluated 6 patients, 4 males and 2 females (5–18 years old and mean age 13.2 years). All of them fulfilled the diagnostic criteria of WS [3] and underwent molecular studies [1] which confirmed the clinical diagnosis. MTSN were found in 2 out of 6 subjects. These 2 girls were 5 and 11 years old. The family history was uneventful with regard to mental retardation, WS and medial telangiectatic nevi. Both showed the clinical phenotype of WS, such as the outgoing, cocktail party behavior, the long face, with full cheeks, flat nasal bridge and malar hypoplasia and a heart defect, i.e. supravalvular aortic stenosis (the older patient) and right axial deviation and neonatal hypercalcemia (the younger patient). Both showed at birth medial telangiectatic nevi on the nape.