Mitochondrial neurogastrointestinal encephalomyopathy syndrome maps to chromosome 22q13.32-qter.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) syndrome is a rare, multisystem disorder characterized clinically by ptosis, progressive external ophthalmoplegia, gastrointestinal dysmotility, leukoencephalopathy, thin body habitus, and myopathy. Laboratory studies reveal defects of oxidative-phosphorylation and multiple mtDNA deletions frequently in skeletal muscle. We studied four ethnically distinct families affected with this apparently autosomal recessive disorder. Probands from each family were shown, by Southern blot, to have multiple mtDNA deletions in skeletal muscle. We mapped the MNGIE locus to 22q13.32-qter, distal to D22S1161, with a maximum two-point LOD score of 6.80 at locus D22S526. Cosegregation of MNGIE with a single chromosomal region in families with diverse ethnic backgrounds suggests that we have mapped an important locus for this disorder. We found no evidence to implicate three candidate genes in this region, by using direct sequence analysis for DNA helicase II and by assaying enzyme activities for arylsulfatase A and carnitine palmitoyltransferase.     

Hypocalcemia and chromosome 22q11 microdeletion

This review of the diagnosis, causes, prevention and treatment of hypocalcemia emphasizes the high incidence of this biological alteration in patients with 22q11 microdeletion. It also points out its large spectrum of presentation, from cases where the most prominent feature of the syndrome is hypocalcemia with hypoparathyroidism, to cases with asymptomatic, latent or late-onset hypocalcemia. Hence, the advice to perform genetic analysis of the 22q11 region in patients with late-onset or recurrent hypoparathyroidism and to systematically include serum calcium in the survey of patients with known 22q11 microdeletion, especially during infancy, adolescence and pregnancy and especially during cardiac surgery or sepsis.     

Seven polymorphic loci mapping to human chromosomal region 11q22-qter

Seven polymorphic loci that map to human chromosomal region 11q22-qter are revealed by DNA probes isolated from a chromosome-specific phage library constructed from a human X mouse somatic cell hybrid that has retained an 11q;16q translocation as the only human DNA. Three probes, each of which reveals a two-allele polymorphism, and four probes, each of which detects two linked RFLPs, have been characterized. Using a somatic cell hybrid mapping panel that divides 11q into four discrete sections, the seven clones have been localized to specific chromosomal regions. Localization of one of the clones has been confirmed and refined by in situ hybridization.     

Isolation of anonymous,polymorphic DNA fragments from human chromosome 22q12-qter

Summary A series of 195 random chromosome 22-specific probes, equivalent to approximately 1% of the size of this chromosome, have been isolated from a chromosome 22-specific bacteriophage lambda genomic library. These probes were mapped to four different regions of chromosome 22 on a panel of five somatic cell hybrids. Restriction fragment length polymorphisms were detected by 28 of the probes mapping to 22q12-qter. Evolutionarily conserved sequences in human, mouse, and Chinese hamster DNA were detected by 12% of the isolated probes.     

Assignment of the myelin basic protein gene to human chromosome 18q22-qter

Summary The assignment of the human myelin basic protein gene to 18q22-qter has been made using a mouse cDNA probe in the study of human-mouse somatic cell hybrids and by in situ hybridization. These results confirm the earlier assignment using in situ studies alone by Saxe et al. (1985).     

The human cytochrome P450 CYP3 locus: assignment to chromosome 7q22-qter

Summary DNA haplotypes (HT) and frameworks (FW) linked to the -globin locus were determined by restriction fragment analysis using eight restriction enzymes on chromosomes bearing the HbA gene (HBB^*A) or the HbE gene (HBB^*E) in the So, an Austro-Asiatic population of northeast Thailand with an HBB^*E frequency near 0.5. All HBB^*E genes were present with FW2, and only two haplotypes were observed (25 HT 27-2,-+-++++-; 10 HT 41-2, +----++-). In a control group from the general population of Northeast Thailand the HT distribution was more diverse, and 2 of 20 HBB^*E genes were present in FW 3. High frequencies of HBB^*E in FW 3 in Southeast Asia are apparently limited to the Khmer population of Cambodia. There were no differences in the hematologic parameters in subjects homozygous for HBB^*E/FW2 or HBB^*E/FW3.     

Monosomy 10q26-qter and trisomy 11q13-qter as a result ofde novo unbalanced translocation

A male infant with partial monosomy 10 q and partial trisomy 11q as a result ofde novo unbalanced translocation between the long arms of chromosomes 10 and 11: der(10)t(10;11)(q26;q13) is described. He had craniofacial dysmorphy, congenital heart defects, urogenital and cerebral anomalies, and severe developmental delay. To the best of our knowledge, this is the first report of this combination of chromosomal abnormalities.     

Genomic disorders on 22q11

The 22q11 region is involved in chromosomal rearrangements that lead to altered gene dosage, resulting in genomic disorders that are characterized by mental retardation and/or congenital malformations. Three such disorders-cat-eye syndrome (CES), der(22) syndrome, and velocardiofacial syndrome/DiGeorge syndrome (VCFS/DGS)-are associated with four, three, and one dose, respectively, of parts of 22q11. The critical region for CES lies centromeric to the deletion region of VCFS/DGS, although, in some cases, the extra material in CES extends across the VCFS/DGS region. The der(22) syndrome region overlaps both the CES region and the VCFS/DGS region. Molecular approaches have revealed a set of common chromosome breakpoints that are shared between the three disorders, implicating specific mechanisms that cause these rearrangements. Most VCFS/DGS and CES rearrangements are likely to occur by homologous recombination events between blocks of low-copy repeats (e.g., LCR22), whereas nonhomologous recombination mechanisms lead to the constitutional t(11;22) translocation. Meiotic nondisjunction events in carriers of the t(11;22) translocation can then lead to offspring with der(22) syndrome. The molecular basis of the clinical phenotype of these genomic disorders has also begun to be addressed. Analysis of both the genomic sequence for the 22q11 interval and the orthologous regions in the mouse has identified >24 genes that are shared between VCFS/DGS and der(22) syndrome and has identified 14 putative genes that are shared between CES and der(22) syndrome. The ability to manipulate the mouse genome aids in the identification of candidate genes in these three syndromes. Research on genomic disorders on 22q11 will continue to expand our knowledge of the mechanisms of chromosomal rearrangements and the molecular basis of their phenotypic consequences.     

Sperm chromosome analysis in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22)

Summary Human sperm chromosomes were studied in a man heterozygous for a paracentric inversion of chromosome 7 (q11q22). The pronuclear chromosomes were analysed after in vitro penetration of golden hamster (Mesocricetus auratus) eggs. Ninety-four sperm chromosome spreads were examined, of which 34 contained the normal number 7 chromosome and 59 the inverted 6. This segregation was significantly different from the expected 1:1 ratio. The number of X- to Y-bearing sperm was 48 and 46 respectively. No sperm contained a recombinant chromosome caused by a crossover within the inversion. The frequency of chromosomal abnormalities in other chromosomes was 9.6%, which is not significantly different from the frequency observed in normal donors (8.9%) in our laboratory. These result suggest that the risk of chromosomally unbalanced sperm is not high for this paracentric inversion.     

Assignment of the human progesterone receptor to the q22 band of chromosome 11

Summary The human progesterone receptor gene was localized by in situ hybridization to the q22 band of chromosome 11.     

Schizophrenia-associated chromosome 11q21 translocation: Identification of flanking markers and development of chromosome 11q fragment hybrids as cloning and mapping resources

Genetic linkage, molecular analysis, and in situ hybridization have identified TYR and D11S388 as markers flanking the chromosome 11 breakpoint in a large pedigree where a balanced translocation, t(1;11)(q43;q21), segregates with schizophrenia and related affective disorders. Somatic cell hybrids, separating the two translocation chromosomes from each other and from the normal homologues, have been produced with the aid of immunomagnetic sorting for chromosome 1– and chromosome 11–encoded cell-surface antigens. The genes for two of these antigens map on either side of the 11q breakpoint. Immunomagnetic bead sorting was also used to isolate two stable X-irradiation hybrids for each cell-surface antigen. Each hybrid carries only chromosome 11 fragments. Translocation and X-irradiation hybrids were analyzed, mainly by PCR, for the presence of 19 chromosome 11 and 4 chromosome 1 markers. Ten newly designed primers are reported. The X-irradiation hybrids were also studied cytogenetically, for human DNA content, by in situ Cot1 DNA hybridization and by painting the Alu-PCR products from these four lines back onto normal human metaphases. The generation of the translocation hybrids and of the chromosome 11q fragment hybrids is a necessary preliminary to determining whether a schizophrenia-predisposition gene SCZD2 is encoded at this site.     

Identification of a new gene locus for adolescent nephronophthisis, on chromosome 3q22 in a large Venezuelan pedigree

Nephronophthisis, an autosomal-recessive cystic kidney disease, is the most frequent monogenic cause for renal failure in childhood. Infantile and juvenile forms of nephronophthisis are known to originate from separate gene loci. We describe here a new disease form, adolescent nephronophthisis, that is clearly distinct by clinical and genetic findings. In a large, 340-member consanguineous Venezuelan kindred, clinical symptoms and renal pathology were evaluated. Onset of terminal renal failure was compared with that in a historical sample of juvenile nephronophthisis. Onset of terminal renal failure in adolescent nephronophthisis occurred significantly later (median age 19 years, quartile borders 16.0 and 25.0 years) than in juvenile nephronophthisis (median age 13.1 years, quartile borders 11.3 and 17.3 years; Wilcoxon test P=.0069). A total-genome scan of linkage analysis was conducted and evaluated by LOD score and total-genome haplotype analyses. A gene locus for adolescent nephronophthisis was localized to a region of homozygosity by descent, on chromosome 3q22, within a critical genetic interval of 2. 4 cM between flanking markers D3S1292 and D3S1238. The maximum LOD score for D3S1273 was 5.90 (maximum recombination fraction.035). This locus is different than that identified for juvenile nephronophthisis. These findings will have implications for diagnosis and genetic counseling in hereditary chronic renal failure and provide the basis for identification of the responsible gene.     

A primary linkage map of the human chromosome 11q22-23 region

We have constructed a genetic map of the human chromosomal region 11q22-23 by multipoint linkage analysis of 13 DNA polymorphisms that we have condensed into eight loci. An analysis for linkage disequilibrium between tightly linked probe/enzyme systems allows us to make specific recommendations for future DNA typing at these loci. The resulting sex-averaged multipoint map spans approximately 80 cM and differs considerably from previously reported genetic maps of this region. Our mathematically derived "most likely order" of the markers is compatible with physical mapping data using somatic cell hybrids. The known localizations of at least 14 functional genes and several disease loci to 11q22-23, including ataxia telangiectasia, make the mapping of this region especially relevant to studies of disease pathogenesis.     

Meiotic chromosome segregation in human t(11;22)(q23;q11) carriers: a theoretical consideration

The t(11;22)(q23;q11) translocation is the most frequently encountered familial reciprocal translocation in humans. In the majority of reported cases ascertainment has been through the birth of a child with the chromosomal constitution 47,XX,+der(22) or 47,XY,+der(22), i.e., tertiary trisomy. Previous segregation analysis of familial cases showed a number of interesting features. Thus, euploid unbalanced genotypes resulting from adjacent segregation are absent in the progeny, and only tertiary trisomic offspring are recovered. To explain this unusual progeny output we present here a model for the meiotic behavior of this translocation in the carriers based on an analysis of cytogenetic data of progeny of carriers. This model predicts the formation of a chain trivalent with chromosome order 11-der(11)-22 during prophase I and its predominant alternate orientation at metaphase I.     

The fragile site on chromosome 16 (q21q22)

Summary The significance of the fragile site on 16 (q21q22) has not yet been fully evaluated. New data will contribute to the understanding of this cytogenetic finding. Therefore we report on four families where a chromosome 16 with fragile site was segregating and such problems as infertility, abortions, malformations, and ancuploidy were present. The hypothesis that this fragile site is a site of viral modification (or integration?) is considered.     

Tertiary trisomy (22q11q),47,+der(22),t(11;22)

Summary We describe a case of tertiary trisomy (22q11q) 47,XX,+der(22),(22pter22q13: : 11q2511qter) in a child with mental retardation, cleft palate, and congenital heart disease resulting from 3: 1 meiotic nondisjunction in a maternal (11;22) translocation carrier. The clinical findings in previously reported cases are reviewed and compared with the features of reported patients with partial trisomy 11q and trisomy 22 syndromes. Half of the ten reported families had additional balanced translocation carriers who may have an increased risk of having a liveborn child with an MCA/MR syndrome, although none have been reported to date.