The link between cytogenetics and mendelism

High resolution chromosome analysis, molecular cytogenetics, and study of the association between specific chromosome rearrangements and single gene disorders have provided a chromosomal basis to a number of mendelian diseases. Deletions and duplications of small regions, usually less than 3 Mb in size, result in an alteration of normal gene dosage of a number of unrelated genes physically close to each other and are responsible for contiguous gene syndromes. For example, haploinsufficiency is implicated for del 8q24.1 in Langer-Giedion syndrome, del 17p13.3 in Miller-Dieker syndrome, and del 22q11.2 in DiGeorge and Velo-cardiofacial syndromes. Another chromosomal mechanism causing mendelian phenotypes is translocation, which may eventually interrupt a disease gene. It is assumed that translocation breakpoints are running through a relevant gene, hindering the production of the gene product. An example is breakage 16p13.3 associated with Rubinstein-Taybi syndrome. Females with X/autosome translocations have an almost exclusive inactivation of the normal X. Interruption of a disease gene in the translocated X causes the expression of a mendelian phenotype in the presence of an allelic recessive mutation onto the nonrearranged X. Finally, if a human gene shows exclusive expression from a single parental homologue, ie, it is imprinted, deletion of the chromosomal segment containing the active allele results in structural monosomy and functional nullisomy. This situation is illustrated by Prader-Willi and Angelman syndromes. Over seventy human genes have been precisely assigned to chromosomal regions using a cytogenetic approach. Chromosome techniques combined with molecular methods have proved to have powerful and sensitive diagnostic capabilities.

A new method for direct analysis of polymerase chain reaction-amplified human papillomavirus using DNA enzyme immunoassay

We describe use of a polymerase chain reaction in conjunction with a DNA enzyme immunoassay for the simultaneous detection of multiple types of human papillomavirus in a single microtiter plate. The method is specific, sensitive, rapid, and capable of detecting human papillomavirus-6, -11, -16, -18, and -33 in cervical biopsy specimens.

A cluster of cystic fibrosis mutations in exon 17b of the CFTR gene: a site for rare mutations

Intensive screening has improved our understanding of the profile of mutations in the CFTR gene in which more than 400 mutations have been detected to date. In collaboration with several European laboratories we are involved in such analysis. We have identified 14 new mutations in exon 17b of CFTR, having analysed 780 CF chromosomes, and have compared the frequency of mutations in this exon with that of other regions of the CFTR gene. The results obtained indicate an accumulation of mutations, not only in regions encoding the two nucleotide binding folds, but also in those encoding transmembrane domains of the CFTR gene, in particular exon 17b.

First-trimester prenatal diagnosis of spinal muscular atrophy using microsatellite markers

Twenty-five pregnancies at risk for spinal muscular atrophy I (SMA I) have been monitored by first-trimester prenatal diagnosis. Microsatellite markers were used in all cases to amplify polymorphic regions at the D5S125, D5S435, D5S39, D5S127, and D5S112 loci. All families, including 12 SMA I pedigrees with a decreased index child, were fully informative for DNA analysis. Three fetuses were predicted to be affected and 22 fetuses were predicted to be unaffected. Twenty-two newborns were unaffected by clinical examination at birth. These results support the accuracy of SMA I prenatal diagnosis based on linkage analysis.

Male hypogonadism in myotonic dystrophy is related to (CTG)n triplet mutation

The Authors considered the relationship between hypogonadism in myotonic dystrophy (MD) and MT-PK gene mutation. Twenty-seven subjects were studied, and the (CTG)n amplification varied from 70 to 1520 (mean 661 +/- 463). Hypergonadotropic-hypogonadism with LH levels of 6.94 +/- 3.87 and FSH 14.54 +/- 9.58 IU/L was present; testosterone still showed normal values (505.7 +/- 376.2 ng/dl), but 44.4% of patients had abnormal serum level less than 250 ng/dl. We found a significant correlation (p < 0.001) between CTG repeat size and levels of both LH and FSH: these findings suggest that the severity of hypogonadism is related to MT-PK gene mutation.

Prenatal diagnosis of X-linked retinitis pigmentosa (RP) in five pregnancies at risk

Five pregnancies at risk for X-linked retinitis pigmentosa (RP) have been monitored by first-trimester prenatal diagnosis using DNA markers flanking the RP2 and RP3 loci. Three affected and two unaffected fetuses, including a female carrying a wild-type genotype, were predicted on the basis of marker segregation and estimation of the recombination fraction.

Human elongation factor EF-1 beta: cloning and characterization of the EF1 beta 5a gene and assignment of EF-1 beta isoforms to chromosomes 2,5,15 and X

We report here the isolation and characterization of a novel human elongation factor-1 beta (EF-1 beta) gene by cDNA selection from YAC mapping on chromosome 5q12-q14. This gene is specifically transcribed in fetal brain and in skeletal muscle and is characterized by a complete sequence homology with previously described EF-1 beta cDNAs. We also assigned the loci for three other EF-1 beta isoforms, to human chromosomes 2, 15 and X. The multiple chromosomal assignments of EF-1 beta loci demonstrates the genetic heterogeneity of human EF-1 beta peptides.

Parental origin of chromosome 4p deletion in Wolf-Hirschhorn syndrome

We report on molecular studies in 7 patients with Wolf-Hirschhorn syndrome (WHC) not showing an obvious chromosome 4p deletion. Analysis of a set of polymorphic probes mapping in the 4p16.3 region showed the absence of paternal haplotypes in 5 cases, and maternal haplotypes in 2. These observations corroborate evidence for preferential paternal origin of the de novo 4p chromosome deletion. The overall results of molecular studies suggest that the preponderance of paternally derived WHC could be due, rather than to imprinting of this region, to an excess of structural rearrangements in the male meiosis, related to differences between the mechanisms of sperm and egg production.

Identification of three novel cystic fibrosis mutations in a sample of Italian cystic fibrosis patients

An analysis of 274 non-delta F508 Italian cystic fibrosis chromosomes was carried out to determine their molecular defect. In a first step, the delta F508 and 59 other mutations were detected by polyacrylamide gel electrophoresis, restriction digestion, and the amplification refractory mutation system (ARMS) technique. The molecular defects of the other chromosomes were screened for by denaturing gradient gel electrophoresis analysis of exons 3, 4, 7, 11, 12, 13, 14a, 17b, 19 and 20. Direct sequencing was carried out if necessary. This approach allowed us to identify 3 novel mutations, namely M348K, D614G and F693L.

Isolation and cloning by a polymerase chain reaction of a genomic DNA fragment of the human slow skeletal troponin (TNNT1) gene

The genomic 3' structure of the gene coding for the human slow skeletal troponin T (TNNT1) gene, is reported. An intron of 912 nucleotides containing an Alu-element has been identified and characterized. The complexity of the sequenced region suggests an alternative exon use. The present results may be valuable for further studies on the gene structure of TNNT1 and the related troponin gene family.

(CTG)n triplet mutation and phenotype manifestations in myotonic dystrophy patients

A genotype-phenotype study based on the primary clinical features of adult myotonic dystrophy (DM) included 116 patients from 62 Italian pedigrees. A significant correlation between clinical severity and the number of repeats at the 3' untranslated region of the myotonin-protein kinase gene (MT-PK) was found. These results suggest that the CTG amplification is directly related to the myotonic dystrophy phenotype and provide important information on morbidity and prognosis in this disease.

A tool for the molecular analysis of an early lethal disease: slide-PCR in spinal muscular atrophy patients

DNA was recovered from sections of muscle biopsies of 20 spinal muscular atrophy (SMA) patients fixed on microscopic slides and stored from one to 20 years at room temperature. Microsatellite DNA markers tightly linked to the SMA locus were amplified using the polymerase chain reaction (PCR) to obtain specific amplified products. The procedure was successful in all cases, and allowed prenatal diagnosis in one at-risk pregnancy. In our hands this procedure is quick, sensitive and reproducible.

Detection by capillary electrophoresis of restriction fragment length polymorphism. Analysis of a polymerase chain reaction-amplified product of the DXS 164 locus in the dystrophin gene

Capillary electrophoresis (CE) was used to characterize restriction fragment length polymorphism (RFLP) in a polymerase chain reaction (PCR)-amplified product of a 740-base pairs DNA fragment from the DXS 164 locus of the dystrophin gene. The polymorphic alleles of 740 and 520/220 base pairs revealed by XmnI digestion were analysed from homozygous and heterozygous individuals by CE. Our studies show that extraction in phenol-chloroform may be useful in PCR-amplified product purification. Excellent separation was obtained in a short time. The data indicate that CE is suitable for genomic analysis such as carrier detection and prenatal diagnosis of X-linked recessive disorders after purification of PCR-amplified products.

Failure in detecting mRNA transcripts from the mutated allele in myotonic dystrophy muscle

The expression of myotonin-protein kinase (MT-PK) gene was studied in myotonic dystrophy (DM) muscle and normal controls using a polymerase chain reaction protocol to analyse the 3' intragenic p(CTG) polymorphism. Unaffected individuals show bi-allelic expression, while the sole wild-type allele was transcribed in DM muscle. Our findings support a gene dosage effect in the pathogenesis of the disease.

Plasmid DNA and low-frequency electromagnetic fields

Physico-chemical and biological properties were studied in recombinant plasmids exposed to electric and magnetic fields (EMFs). The absence of slow-migrating DNA species and failure to identify induced DNA conformers, suggests that EMFs do not have any obvious genotoxic effect in any of the experimentally tested conditions.

Polymerase chain reaction in the detection of mRNA transcripts from the slow skeletal troponin T (TNNT1) gene in myotonic dystrophy and normal muscle

Recent studies have shown that the gene encoding for the slow skeletal troponin isoform T (TNNT1) is located on the proximal long arm of human chromosome 19 in the myotonic dystrophy (DM) region. In order to test TNNT1 as a candidate gene for DM, we have isolated TNNT1 cDNA from skeletal muscle from two healthy individuals and from two patients with DM. Sequencing of the TNNT1 cDNA from the DM and normal muscle revealed two sequence variants but no transcriptionally significant mutations. This work rules out a defect in the coding segment of TNNT1 as a cause of DM and provides a polymerase chain reaction protocol for studying troponin T gene expression.

Expansion of the myotonic dystrophy gene in Italian and Spanish patients

Myotonic dystrophy results from expansion of a (CTG)n repeat at the 3' untranslated region of the myotonin-protein kinase gene. We show here the genomic analysis of 322 symptomatic patients with the cDNA-25 probe detecting disease specific EcoRI restriction fragments. The expansion was found in the majority of Italian and Spanish patients (92%). The implications of these results for the detection of symptomatic patients in southern Europe are discussed.

[The correlation between the genotype and the clinical expression of cystic fibrosis]

The authors report a phenotype-genotype correlation in a population of patients from center and south Italy affected by cystic fibrosis (CF). Thirteen (21%) of patients with pancreatic insufficiency (PI) were homozygous for delta F508, seventeen (27%) were delta F508 heterozygous with an associated unknown allele. Two other described mutations (N1303K, G542X) were also found in a heterozygote status and associated with a severe clinical expression of disease.

The prevalence of HPV16DNA in normal and pathological cervical scrapes using the polymerase chain reaction

Human papillomavirus (HPV) has been implicated in the development of cervical cancer. Newly developed molecular techniques have facilitated HPV identification and typing of cervical lesions. Several studies have suggested a strong correlation between HPV16 and intraepithelial cervical neoplasia. However, there is no agreement on this point since HPV16 is detected also in normal cervical tissue. We have amplified the L1 region of HPV16 DNA using the polymerase chain reaction (PCR) technique and analyzed the HPV16 prevalence in cytological scrapes of 201 Italian sexually active patients. One hundred twenty-four of these women had normal cytologic and colposcopic examination, while seventy-seven women had normal or abnormal cytology and a cervical lesion detectable by colposcopy. Within this latter group, 25 of 77 women (32.4%) were positive for HPV16 DNA, compared to 11 of 124 samples (8.87%) from women with normal cytology and colposcopy. The present results confirm the high efficiency of the PCR technique in detecting HPV16 DNA from cervical scrapes and suggest that this analysis should become a method of choice in clinical studies.

A frameshift mutation (2869insG) in the second transmembrane domain of the CFTR gene: identification, regional distribution, and clinical presentation

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DNA markers in diagnosis of adult dominant polycystic kidney disease

We report the results of a biological and molecular study carried out on 11 Italian families, with a total of 111 individuals in which adult dominant polycystic kidney disease segregates. A restriction fragment length polymorphism analysis was performed. Two families have shown a genetic heterogeneity even if not phenotypically different from the other ones: they resulted unlinked to 16p markers. A prenatal diagnosis has been performed in a family of the linked type.

Inosine-containing primers in human papillomavirus detection by polymerase chain reaction

A PCR protocol has been developed using inosine-containing primers for human papilloma virus (HPV) detection. The HPV16 L1 region from CaSki-positive cells was efficiently amplified by a single reaction and directly analyzed by agarose gel electrophoresis. The method was found to be sensitive and reproducible, and it easy to use for HPV typing and screening.

Analysis of 14 cystic fibrosis mutations in five south European populations

We have analysed five Southern European populations (Albanian, Greek, Italian, Spanish and Yugoslavian) for 14 cystic fibrosis (CF) mutations. The most frequent mutations, apart from delta F508, were G542X (6.04%), R1162X (3.61%) and N1303K (3.24%). Each of the other analysed mutations were present at a frequency of less than 1% (R347P, R334W, S549RA, S549I, G551D, R553X and W1282X), and four mutations (D110H, delta I507, S549RT, and S1255X) were not found in this sample. The data presented here allows the use of mutation analysis in 69.5% of Spanish, 58% of Greek, and 56.5% of Italian CF cases.

3' creatine kinase (M-type) polymorphisms linked to myotonic dystrophy in Italian and Spanish populations

Linkage analysis and haplotype characterization for the allelic system detected at the 3' creatine kinase muscle type (CKMM) locus were carried out in 59 myotonic dystrophy (DM) families from Italy and Spain. A maximum lod score (zmax) of 21.26 at a recombination frequency (theta) of 0.00 was found. No statistically significant linkage disequilibrium was observed between DM and the RFLPs examined. However, a substantial linkage disequilibrium was found between CKMM-TaqI and CKMM-NcoI sites in these two populations.

The search for south European cystic fibrosis mutations: identification of two new mutations, four variants, and intronic sequences

The major mutation in the cystic fibrosis (CF) gene is a 3-bp deletion (delta F508) in exon 10. About 50% of the CF chromosomes in Southern Europe carry this mutation, while other previously described mutations account for less than 4%. To identify other common mutations in CF patients from the Mediterranean area, we have sequenced, exon by exon, 16 chromosomes that did not show the delta F508 deletion from a selected panel of eight unrelated CF patients. We describe here one missense and one nonsense mutation, and four sequence polymorphisms. We have also found two previously reported mutations in three chromosomes. Overall, these mutations may account for about 20% of CF alleles in the Italian and Spanish populations. No other mutations were detected in 10 out of 16 CF chromosomes after analyzing about 90% of the coding region of the CF gene, and 39 out of 54 intron/exon boundaries. Therefore, about 26% of CF mutations remain to be identified. In addition we provide the intron/exon boundary sequences for exons 4 to 9. These results together with previously reported linkage data suggest that in the Mediterranean populations further mutations may lie in the promoter region, or in intron sequences not yet analyzed.

Forensic applications of molecular genetic analysis: an Italian collaborative study on paternity testing by the determination of variable number of tandem repeat DNA polymorphisms

Several variable number of tandem repeat (VNTR) DNA polymorphisms detecting different loci (YNH24/MspI or TaqI, CMM101/MspI or MLJ14/MspI, EFD64.2/RsaI or HinfI, YNZ22/TaqI, AW101/EcoRI, EKMDA2.1/PvuII and 3'-HVR/PvuII) were used in the analysis of 27 cases of disputed paternity in the Italian population. Fourteen exclusions and 17 attributions were performed. The results were compared with those obtained with immunohematologic analyses. Four exclusions and 2 attributions were made possible only by the combined use of several DNA polymorphisms, as the analyses of red-blood-cell antigens and isoenzymes, serum proteins and HLA group determinants were inconclusive. With the DNA test, 10 exclusions and 15 attributions were confirmed, with increased overall probability. In conclusion, VNTR polymorphisms were more informative, accurate and sensitive than the immunohematologic tests. Therefore, DNA analysis is the method of choice for testing genetic relationships.

Study of the effects on DNA of electromagnetic fields using clamped homogeneous electric field gel electrophoresis

A clamped homogeneous electric field (CHEF) electrophoresis allowing the separation of DNA molecules in the range of 200 to 3000 kb in size was used to study the biological effects of electric and magnetic fields (EMFs). The results obtained did not show any detectable genomic damage on Saccharomyces cerevisiae.

[The role of endoscopy in the hemorrhagic complications of gastroduodenal ulcer]

The hemorrhage is a fairly frequent event in the evolution of the gastroduodenal peptic ulcer syndrome. The mortality rate has remained approximately unchanged, in spite of the progress in instrumental diagnosis and medical therapy, in the last decade. The authors examine 163 cases of digestive hemorrhage from gastroduodenal ulcers, observed in the last five years (1984-1988), with particular reference to the medical or surgical treatment undertaken, and to the mortality rate. Gastroduodenal ulcers, in 340 cases of upper digestive hemorrhage, represented nearly half the lesions, registered in the same period. Duodenal ulcers (D.U.), were found in 124 patients (34.4%) and gastric ulcers (G.U.) in 39 patients (11.47%), 113 (91.1%) patients with D.U., and 33 (84.6%) patients with G.U. were treated by medical therapy. The mortality rate in this group was 6.16%. II patients (8.9%) with D.U. and 6 patients (15.3%) with G.U. were operated on. The surgical mortality rate was high at 35.2%. Total mortality rate was 9.2%. The endoscopic exam was useful for diagnostic bleeding investigation and contributed to therapeutic decisions. Active bleeding lesions were found in 38.4% of patients with G.U. and in 32.3% with D.U. In 61.6% of patients with G.U. and in 67.7% with D.U., the lesions had already stopped bleeding; but in both lesions nearly 40% of cases, presented signs of a recent hemorrhage. The prognosis and natural history of the hemorrhage, was not changed by an immediate exam. The clinical reports and the data furnished, especially from continuous bleeding and rebleeding lesions, could be useful in identifying a sub-group of patients who could obtain better results by surgical treatment within a suitable time. The endoscopy, besides selecting and contributing to a better therapeutic strategy, through haemostasis technic, could reduce mortality rate from gastroduodenal ulcer lesions.

A 45,X male with molecular evidence of a translocation of Y euchromatin onto chromosome 1

A 45,X complement was found in lymphocyte and fibroblast cultures of a male infant with severe growth and mental retardation and mild dysmorphism. Lymphocyte DNA from this patient was found to contain Yp chromosome sequences. In situ hybridization (ISH) with the 50f2 probe led to a clear assignment of euchromatic material on the short arm of chromosome 1. This observation and others from the literature argue in favour of the conclusion that all 45,X males are probably either the result of undetected mosaicism or are carriers of Y translocated material.

Characterization of deletions in the dystrophin gene giving mild phenotypes

We have characterized deletions of the dystrophin gene in patients suffering from relatively mild muscular dystrophy. Our data show that most of the Becker muscular dystrophy (BMD) patients have intragenic deletions which leave the protein reading frame in phase. Remarkably, large deletions of the region corresponding to the central triple helical repeats in the protein can result in an exceptionally mild phenotype. Three brothers suffering from BMD, glycerol kinase deficiency, and adrenal hypoplasia possess a deletion at the 3' end of the gene. They also display developmental delay. Thus the 3' processing of the gene must be necessary for the correct function of the dystrophin molecule.