Elisabetta Lenzini

Duplication of an Xp segment that includes the ZFX locus causes sex inversion in man

SummaryTwo 46,XY females with tandem duplications of an X short arm segment were studied by cytogenetic and Southern blot analysis. The results show that the duplicated segment in each case included the Xp21.2–Xp22.2 interval, resulting in a double dose of ZFX on the single active X chromosome. The results from our two cases, in conjunction with those reported by other workers, lead us to conclude that the duplication is the reason for the sex inversion. If ZFY and ZFX are indeed sex-determining gene loci, these findings favour a model of sex determination characterized by antagonistic interaction between these genes.

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.

Cytogenetic and molecular evaluation of 241 small supernumerary marker chromosomes: cooperative study of 19 Italian laboratories

Purpose: We evaluated the experiences of 19 Italian laboratories concerning 241 small supernumerary marker chromosomes (sSMCs) with the aim of answering questions arising from their origin from any chromosome, their variable size and genetic content, and their impact on the carriers phenotype.Methods: Conventional protocols were used to set up the cultures and chromosome preparations. Both commercial and homemade probes were used for the fluorescent in situ hybridization analyses.Results: A total of 113 of the 241 sSMCs were detected antenatally, and 128 were detected postnatally. There were 52 inherited and 172 de novo cases. Abnormal phenotype was present in 137 cases (57%), 38 of which were antenatally diagnosed. A mosaic condition was observed in 87 cases (36%). In terms of morphology, monocentric and dicentric bisatellited marker chromosomes were the most common, followed by monocentric rings and short-arm isochromosomes. The chromosomes generating the sSMCs were acrocentric in 132 cases (69%) and non-acrocentric chromosomes in 60 cases (31%); a neocentromere was hypothesized in three cases involving chromosomes 6, 8, and 15.Conclusion: The presented and published data still do not allow any definite conclusions to be drawn concerning karyotype–phenotype correlations. Only concerted efforts to characterize molecularly the sSMCs associated or not with a clinical phenotype can yield results suitable for addressing karyotype–phenotype correlations in support of genetic counseling.

Concomitant Amplif ication and Expression of PAX7-FKHR and MYCN in a Human Rhabdomyosarcoma Cell Line Carrying a Cryptic t(1;13)(p36;q14)

Alveolar rhabdomyosarcoma (ARMS) is associated with the specific chromosomal translocation (2;13)(q35;q14) or its rarer variant t(1;13)(p36;q14), which produces the fusion gene PAX7-FKHR. Here we describe the human cell line RC2, derived from an ARMS, which harbors a cryptic t(1;13)(p36;q14) and concomitantly shows amplification of the PAX7-FKHR fusion gene and of the MYCN oncogene. The t(1;13) and MYCN oncogene were studied by standard cytogenetic analysis and molecular techniques. The reverse transcriptase polymerase chain reaction demonstrated the expression of PAX7-FKHR mRNA in RC2 cells, although karyotype analysis failed to demonstrate a t(1;13)(p36;q14) chromosomal translocation or a derivative 13 chromosome. Double minute chromosomes were detected in all the metaphases studied. Fluorescence in situ hybridization analysis revealed multiple copies of the PAX7-FKHR fusion gene localized exclusively on a subset of double minutes, whereas multiple copies of MYCN were identified on other double minute chromosomes. Southern-blot analysis demonstrated that RC2 cells contain approximately 20 copies of the MYCN oncogene. So far no continuous RMS cell line carrying the t(1;13)(p36;q14) has been described, and PAX7-FKHR and MYCN amplifications have always been reported to occur separately in rhabdomyosarcoma (RMS). The availability of an ARMS cell line that harbors the t(1;13)(p36;q14) constitutes a useful tool for further understanding the role of the PAX7-FKHR fusion gene in RMS oncogenesis and may improve knowledge of the possible relation between PAX7-FKHR and MYCN amplification.

Cytogenetic findings in 4952 prenatal diagnoses. An Italian collaborative study

SummaryThe development of prenatal diagnosis in Italy was made difficult by the restrictions of the old abortion law and only in recent years has a consistent number of cases been investigated. We report the experience on prenatal chromosome diagnosis of ten Italian centers participating in a collaborative study on 4952 diagnoses performed from 1972 to 1980. The main indication groups were: advanced maternal age (2882 cases), previous child with chromosome anomaly from parents with normal karyotype (847 cases), and chromosome anomaly in one parent (97 cases). The other indications for amniocentesis, including cases without a cytogenetic risk, have been assembled into a “miscellaneous” group (1126 cases). We found 125 abnormal fetal karyotypes (2.5%) of which 89 were unbalanced (1.8%). The frequencies and types of chromosome anomalies are reported in detail for each indication group and are compared with the corresponding ones from the European Munich Conference. The great majority of these Italian data were not included in the Munich report.

Study on segregation and risk for abnormal offspring in carriers of pericentric inversion of the (p11←q13) segment of chromosome 2

Pericentric inversion of chromosome 2 was detected in four unrelated families. All these inversions involved the segment p11←q13. The pedigree data are considered in comparison with other cases reported in the literature. Segregation data and possible reproductive failures are discussed.

Functional analysis of missense mutations of OAT, causing gyrate atrophy of choroid and retina.

We studied eight kindreds with gyrate atrophy of choroid and retina (GA), a rare autosomal recessive disorder caused by mutations of the OAT gene, encoding the homoexameric enzyme ornithine‐delta‐aminotransferase. We identified four novel and five previously reported mutations. Missense alleles were expressed in yeast strain carrying a deletion of the orthologous of human OAT. All mutations markedly reduced enzymatic activity. However, the effect on the yeast growth was variable, suggesting that some mutations retain residual activity, below the threshold of the enzymatic assay. Mutant proteins were either highly unstable and rapidly degraded, or failed to assemble to form the active OAT hexamer. Where possible, fibroblast analysis confirmed these data. We found no correlation between the residual enzymatic activity and the age of onset, or the severity of symptoms. Moreover, the response to B6 was apparently not related to the specific mutations carried by patients. Overall these data suggest that other factors besides the specific OAT genotype modulate (GA) phenotype in patients. Finally, we found that 5‐aminoimidazole‐4‐carboxamide ribonucleoside (AICAR), an AMPK activator known to increase mitochondrial biogenesis, markedly stimulates OAT expression, thus representing a possible treatment for a subset of GA patients with hypomorphic alleles.

Frequency of abnormal karyotypes in relation to the ascertainment method in females referred for suspected sex chromosome abnormality

Cytogenetic investigation was carried out on 231 female patients referred for suspected sex chromosome abnormality. Cases were classified into five groups according to reason for referral and chromosome abnormality frequency was estimated. The overall frequency of abnormal karyotypes was 38.5%. The rate of positive identification of chromosome abnormality ranges from 0 in patients with secondary amenorrhoea to 80% in those with Turner phenotype. Our data demonstrate that the indications for referral of female patients with suspected sex chromosome abnormality are not only primary amenorrhoea alone or short stature and primary amenorrhoea without Turner stigmata, but also short stature of unknown etiology without any additional anomaly during childhood.

Prenatal diagnosis of Miller-Dieker syndrome by ultrasound and molecular cytogenetic analysis

To the Editor: Among malformations as a result of abnormal neuronal migration, lissencephaly is the most relevant, characterizing Miller–Dieker syndrome (MDS; MIM 24720) and isolated lissencephaly sequence (ILS; MIM 607432) (1–3). MDS is a rare developmental disorder resulting in agyria/ pachygyria with microcephaly, characteristic dysmorphisms (prominent forehead, short nose, thickened upper lip, low-set ears, and small jaw), renal, gastrointestinal, cardiac anomalies, Intrauterine Growth Retardation (IUGR), polyhydramnios, low birth-weight, mental retardation, and seizures (3, 4–11). MDS is associated with deletions of 17p13.3 band. The rearrangement is familial in 20% patients (12). ILS is characterized by the absence of sulci and gyri without other major malformations (13), the lissencephaly degree is less severe (4). In both syndromes, lissencephaly can be discovered prenatally by 24–26 weeks (10). We report a pre-natal diagnosis of MDS because of a de novo rearrangement between 17p and 18p. A woman (31-years) was referred at 29th week for polyhydramnios. There was no family history of genetic disorders. Fetal Ultrasound (US) revealed polyhydramnios, IUGR, head circumference of 246 mm, biparietal diameter of 68 mm, ventriculomegaly, dysgenetic corpus callosum, hypoechogenic cerebral parenchyma, pachygyria, equinovarus foot, and hyperechoic renal parenchyma. Amniocentesis and cordocentesis for cytogenetic analysis lead to the diagnosis of MDS. Fetal death occurred at 38th week. Post-mortem examination: brain weight of 293 g, cortex surface completely smooth (agyria), ventricular dilation mostly in median/posterior areas. Microscopic examination: abnormally thickened (8.5–10 mm) and four-layered’ cortex (molecular layer, thin layer of large neuronal cells, tangential plexus of myelinic fibers with few neuronal cells, thick layer of sparse and disorganized neuronal cells, and hypoplasia of pyramidal neurons); deep cortical layer not fused with the neocortex, constituting a subcortical mass of gray matter. Left talipes equinovarus was observed, but no other major malformations. Chromosomal analysis (QFQ) on amniotic fluid and fetal blood cells revealed an apparently balanced karyotype: 46,XX,t(17;18)(p13;p11.2) in both tissues (Fig. 1a). Parents karyotype was normal. Despite the apparently balanced translocation, ultrasonographic results suggested MDS and 17p microdeletion. Fluorescent in situ hybridization (FISH) studies (telVysion 282M15, D18S552 Vysis), showed absence of the signal for the subtelomeric region 17p on the derivative chromosome 18 and presence of a signal for the subtelomeric region 18p on the derivative chromosome 17. Probes for gene LIS1 locus for lissencephaly in MDS and for the gene FLI locus in the critical region for Smith–Magenis syndrome (17p11.2) (Cytocell) revealed absence of the signal for LIS1 and presence of the signal for FLI (Fig. 1b–d), revealing a submicroscopic deletion in the subtelomeric region 17p including the LIS1 gene. Karyotype was redefined. Eight marker microsatellites distributed in a region of 10.7 Mb with a telomeric localization between 17p13.3 and 17p13.1 were used; a deletion of 4 Mb and the maternal origin of the derivative chromosome 17 were found. Mutations of LIS1 gene are responsible of lissencephaly in MDS and ILS (14). Other additional genes distal to LIS1 seem to determine facial dimorphisms and the more severe lissencephaly seen in MDS. Cardoso et al. (4) demonstrated that MDS is caused by haploinsufficiency of at least nine genes including LIS1 (14-3-3e,

1q44-qter Trisomy:Clinical Report and Review of the Literature

Subtelomeric rearrangements are one of the main causes of multiple congenital anomalies and mental retardation, and they are detected in 5% of patients. We report on a 6.5-year-old boy with mental retardation, dysmorphic features, and behavioral problems, who revealed 1q44-qter trisomy and 22q13.3-qter monosomy due to a maternal cryptic translocation t(1;22). We compared the clinical and cytogenetic data of our patient with those of another case presenting a pure 22qter monosomy and with those of all 1qter trisomy cases reported in the international literature. To the best of our knowledge, the subterminal 1q trisomy found in the present case has been reported in only 12 patients to date (including five familial cases). This report aims to contribute to our understanding of 1q44-qter trisomy.