Complete screening of the CFTR gene in Argentine cystic fibrosis patients

In order to establish the nature and the distribution of mutations causing cystic fibrosis (CF) in 220 unrelated Argentine families, the present authors conducted an extensive molecular analysis of the CF transmembrane regulator (CFTR) gene. First, a direct mutation analysis of 13 common mutations was done, enabling the detection of 319 out of 440 CF alleles (72.52%). Then an exhaustive screening of the entire coding region and the adjacent sequences of the CFTR gene was performed in all patients carrying at least one unidentified CF allele using the multiplex heteroduplex analysis assay followed by direct DNA sequencing. Thirty-nine different CF mutations, including five previously undescribed mutations (i.e. L6V, Y362X, 1353insT, 2594delGT and 2686insT) and two novel polymorphisms (i.e. 1170G/C and 3315A/C) were identified. As a result, the overall detection rate increased by up to 83.45%. Besides DeltaF508, only five mutations showed frequencies higher than 1%. In addition, a total of 49% of the mutations were rare because they were found in only one CF family. This wide spectrum of CF mutations is in agreement with the heterogeneous ethnic origin of the Argentine population. The data obtained here may have important consequences for the development of adequate strategies for the molecular diagnosis of CF in Argentina.

Organization and transcriptional analysis of a six-gene cluster around the rplK-rplA operon of Corynebacterium glutamicum encoding the ribosomal proteins L11 and L1

A cluster of six genes, tRNA(Trp)-secE-nusG-rplK-rplA-pkwR, was cloned and sequenced from a Corynebacterium glutamicum cosmid library and shown to be contiguous in the C. glutamicum genome. These genes encode a tryptophanyl tRNA, the protein translocase component SecE, the antiterminator protein NusG, and the ribosomal proteins L11 and L1 in addition to PkwR, a putative regulatory protein of the LacI-GalR family. S1 nuclease mapping analysis revealed that nusG and rplK are expressed as separate transcriptional units and rplK and rplA are cotranscribed as a single mRNA. A 19-nucleotide inverted repeat that appears to correspond to a transcriptional terminator was located in the 3' region downstream from nusG. Northern analysis with different probes confirmed the S1 mapping results and showed that the secE-rplA four-gene region gives rise to four transcripts. secE was transcribed as a 0.5-kb monocistronic mRNA, nusG formed two transcripts of 1.4 and 1.0 kb from different initiation sites, and the two ribosomal protein genes rplK and rplA were cotranscribed as a single mRNA of 1.6 kb. A consensus L1 protein binding sequence was identified in the leader region of the rplK-rplA transcript, suggesting that expression of the rplK-rplA cluster was regulated by autogenous regulation exerted by the L1 protein at the translation level. The promoters of the nusG and rplK-rplA genes were subcloned in a novel corynebacterial promoter-probe vector and shown to confer strong expression of the reporter gene.

Spondylo-meta-epiphyseal dysplasia, short limbs, abnormal calcification type: a new case with severe neurological involvement

A case of an affected girl with spondylo-meta-epiphyseal dysplasia (SMED) is reported. The disease was detected at birth as a congenital dysplasia with generalized lesions. At 10 months of age, abnormal calcifications appeared in both wrists. The patient evolved with severe growth retardation and multiple neurological and respiratory complications, followed by death at 21 months of age.

Characterization of the ribosomal rrnD operon of the cephamycin-producer 'Nocardia lactamdurans' shows that this actinomycete belongs to the genus Amycolatopsis

The cephamycin producer strain 'Nocardia lactamdurans' contains four ribosomal RNA (rrn) operons. One of them (rrnD) was cloned from a DNA library in the bifunctional cosmid pJAR4. A 2229 bp region of rrnD has been sequenced. The 'N. lactamdurans' rrnD operon maintains the canonical order 5'-16S-23S-5S-3'. Four of the consensus Gürtler-Stanisch sequences were found in the 16S rRNA gene and a fifth one in the sequenced 5' region of the 23S rRNA gene. The anti Shine-Dalgarno sequence of 'N. lactamdurans' (located in the 3'-end of the 16S rRNA gene) was found to be 5'-CCUCCUUUCU-3' and is identical to that of Corynebacterium lactofermentum and Mycobacterium tuberculosis. A phylogenetic analysis of 'N. lactamdurans' by the neighbor-joining method using the entire 16S rRNA nucleotide sequence revealed that this actinomycete is closely related to Amlycolatopsis orientalis subsp orientalis, Amycolatopsis coloradensis, Amycolatopsis alba, Amycolatopsis sulphurea and other Amycolatopsis sp. but only distantly related to species of the genus Nocardia. The cephamycin producer 'N. lactamdurans' NRRL 3802 should be, therefore, classified as Amycolatopsis lactamdurans. The deduced secondary structure of the 16S rRNA is very similar to that of A. colorandensis and A. alba but different from those of species of the Nocardia genus supporting the incorporation of 'N. lactamdurans' into the genus Amycolatopsis.

Carrier detection in Duchenne and Becker muscular dystrophy Argentine families

In order to offer carrier detection, genetic counseling, and prenatal diagnosis to families with Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) in our country, segregation analysis of highly polymorphic short tandem repeats (STR) (dC-dA)n: (dG-dT)n loci was utilized. The risks to females of 15 DMD BMD families (9 familial and 6 sporadic) were evaluated on STR, pedigree and serum creatine kinase (SCK) data. From the 36 females at risk of being carriers (not including 8 obligate carriers), results of STR analysis were compatible with carrier status in 7 and not compatible in 20. In 9 females, no information regarding carriership was derived from the STR analysis. Prenatal diagnosis is now possible on the carrier females. Previously identified deletions in the central part of the gene were confirmed by STR analysis in 3 families. Five new alleles were identified in Argentine individuals; allele frequencies differed from those of North American people. Results derived from this study are useful for carrier detection and genetic counseling in DMD/BMD. One case of probable mosaicism in an unaffected father was detected on a pedigree basis in a family with DMD patients.

Fragile X founder effects in Argentina

To investigate the origin of fragile X mutations in the Argentine population, we studied the alleles and haplotypes at DXS548 and FRAXAC1 loci of 42 unrelated fragile X chromosomes and 168 normal ones. Four haplotypes presented in linkage disequilibrium and accounted for 76.2% of fragile X chromosomes, representing the high frequency of haplotype DXS548-FRAXAC1 7-1 (26.2%) characteristic of our population. FRAXAC1 allele 1 was observed on 47.6% of fragile X chromosomes. Thus, we provide evidence for fragile X founder effects in the Argentine population, similar to those observed in Caucasians and in Asians.

Deletion patterns in Argentine patients with Duchenne and Becker muscular dystrophy

The identification of mutations in Duchenne or Becker muscular dystrophy (DMD/BMD) patients is important for carrier detection in these families. We present the patterns of deletions of the dystrophin gene in Argentine population. DNA from 75 patients with DMD/BMD was analyzed by multiplex PCR and, in some cases, cDNA/Southern. Deletions were detected in 24 patients (32%) and were mainly clustered in two areas of the dystrophin gene: the 5' end (exons 3-12) and the central part (exons 44-53). 64% of the deletion endpoints lay in the middle region and 34% in the 5' end of the gene. The most frequent sites for deletion-endpoints were in the introns 47 (13.6%), 44 (11%), 2 (9%) and 12 (7%). Thus, the proportion and distribution of deletions in our DMD/BMD patients differ from those reported for other populations. Furthermore, a higher proportion of deletions was observed in familial cases (40%) than in isolated ones (30%), in contrast to previously reported data. The effect of the deletion on the reading frame agree with the phenotype in almost all the patients studied. This study will be useful in prenatal diagnosis and diagnosis of other Argentine DMD patients.

Clinical, cytogenetic, and molecular testing of Argentine patients with retinoblastoma

PURPOSE

The purpose of this study is to determine the clinical, chromosomal, and molecular characteristics of Argentine patients with unilateral and bilateral retinoblastoma.

STUDY DESIGN

Eighty-six patients belonging to 82 families were studied; 59% of them were examined during the first year of life. Leukocoria was the most common reason for consultation. Other presenting signs were strabismus and glaucoma. Enucleation of the affected eye was performed in 85% of the cases and the complication rate was 13%.

RESULTS

An appropriate therapy allowed the survival of 84 of the 86 patients. Two children with malformations and growth retardation had an abnormal karyotype with a deletion in 13q14. Segregation analysis of polymorphic sites within the retinoblastoma gene and the parental origin of the allele lost in the tumor were analyzed in 30 of the 82 families. Five mutant alleles transmitted through the germline and six de novo germline mutant alleles were identified in 12 patients with hereditary retinoblastoma. Most de novo germline mutant alleles were paternally derived. Molecular analysis of nonhereditary retinoblastoma showed loss of heterozygosity in three of eight cases. From these, two maternal alleles and one paternal allele were lost, thus not indicating a significant difference in the parental origin for the lost allele.

CONCLUSIONS

These data are useful for deoxyribonucleic acid diagnosis of susceptibility to retinoblastoma in relatives of hereditary patients, even if mutations have not been identified.

Spectrum of CFTR mutations in Argentine cystic fibrosis patients

The identification of different mutations which cause cystic fibrosis (CF) in Argentine patients has been performed. Initially, 10 of the most commonly mutated loci in 228 independent chromosomes were analyzed. Each allele was detected by PCR amplification of DNA samples either directly on polyacrylamide gels, by restriction enzyme digestion and agarose gels electrophoresis, or by hybridization with allele specific oligonucleotides. The delta F508 mutation was found in 57% of the alleles. The frequencies of the other CF mutations were as follows: G542X 3.9%, W1282X 3.1%, N1303K 1.7%, 1717 1-G-->A 0.9%, R553X 0.4%, R1162X 0.4%, whereas G551D, delta I507 and S549N were not found. This direct mutation analysis enabled the detection of 155/228 CF alleles (67%). Of the remaining 73 unidentified CF alleles, 22 were investigated for the 27 exons by DGGE and 9 rare mutations were identified. The incidence of the main CF mutations analyzed was similar to that of the South European population and markedly different from other Latin American countries. The mutation data presented here may be useful for designing DNA testing strategies for CF in Argentina.

Tandem triplication and quadruplication of chromosome 21 in childhood acute lymphoblastic leukemia

A 5-year-old girl with ALL was shown to have a leukemic clone characterized by a triplication and quadruplication of chromosome 21, arranged in tandem, at diagnosis and relapse, respectively. To our knowledge, this is the second report of this chromosomal anomaly in ALL, which was confirmed by in situ staining. The karyotype evolution in the leukemic clone from triplication to quadruplication at relapse emphasizes the association of chromosome 21 with hematopoietic malignancies.

Autosomal dominant neuromuscular disease with cylindrical spirals

Cylindrical spirals (CS) have been reported in muscle biopsies from five individual cases, as well as in two belonging to one family where there was another affected member, clinically associated with cramps, pain, stiffness and/or weakness. Here we studied muscle biopsies of a 70-yr-old mother and her 52-yr-old son, the latter with an associated neuropathy, both with late clinical onset in whose family at least 10 other members, spanning five generations, were diversely affected by muscular weakness, gait disorders, motor impairment and/or scoliosis, featuring an autosomal dominant trait with variable expression. CS as the main pathological findings were observed by light microscopy mostly in type 2 fibres, consisting of subsarcolemmal or intermyofibrillar granular and/or rod-like clusters, bluish with haematoxylin, bright red with Gomori's modified trichrome, non- or lightly reactive with PAS, faintly coloured with NADH-TR, non-reactive with SDH or ATPase, strongly stained with non-specific esterase and myoadenylate deaminase. Ultrastructurally, CS appeared as concentrically wrapped lamellae 1-2 microns in diameter. On occasion CS merged into tubular vesicular structures strongly resembling tubular aggregates (TA). Dilation of terminal cisternae (TC) in their proximity supports an origin from the sarcoplasmic reticulum (SR). Variable gene expression possibly explains both the highly diverse clinical compromise and time of onset.

Two brothers with Martsolf's syndrome

Two brothers affected by a syndrome consisting of short stature, hypogonadism, and severe mental retardation are reported. The syndrome shares the features of that described by Martsolf et al in two brothers born to a consanguineous Polish Jewish couple. Although our patients' parents are Sephardic Jews, they deny consanguinity. These observations and personal knowledge of another affected Jewish boy raise the question of whether Martsolf's syndrome is a new entity that should be included in the group of those that affect mainly Jewish people, and whether its pattern of inheritance is X linked recessive or autosomal recessive limited to males.

[Incontinentia pigmenti. Concerning 9 new cases, 2 of them associated with different genetic syndromes]

Nine girls with Incontinentia Pigmenti are presented, two of them associated to different genetic syndromes. All the patients are female, characteristic of genetic transmission, linked to dominant x, lethal for males; one of the patients also presents the Larsen Syndrome and another has got her illness associated to the Chotzen Syndrome; in these cases we can observe the coexistence of two syndromes, genetically determined. A revision of the clinical, histopathological and genetic characteristics of this disease is made.