Athena Milatovich

The CD40 ligand, gp39, is defective in activated T cells from patients with X-linked hyper-IgM syndrome.

The prominent role of the CD40 receptor in B cell responses led us to investigate the role of the gp39-CD40 interaction in a group of primary immunodeficient patients with defective antibody production. Here we report that patients with hyper-IgM syndrome (HIM) have a defective gp39-CD40 interaction. B cells from HIM patients express functional CD40, but their T cells do not bind CD40-Ig. These patients expressed normal levels of gp39 mRNA, but these mRNAs encode defective gp39 proteins owing to mutations in the extracellular domain of gp39. Soluble recombinant forms of gp39 containing these mutations were unable to bind CD40 and drive normal B cell proliferation. The gene encoding gp39 was mapped to Xq26, the X chromosome region where the gene responsible for HIM had previously been mapped. These data suggest that a defect in gp39 is the basis of X-linked HIM.

Molecular genetics of steroid 5 alpha-reductase 2 deficiency.

Two isozymes of steroid 5 alpha-reductase encoded by separate loci catalyze the conversion of testosterone to dihydrotestosterone. Inherited defects in the type 2 isozyme lead to male pseudohermaphroditism in which affected males have a normal internal urogenital tract but external genitalia resembling those of a female. The 5 alpha-reductase type 2 gene (gene symbol SRD5A2) was cloned and shown to contain five exons and four introns. The gene was localized to chromosome 2 band p23 by somatic cell hybrid mapping and chromosomal in situ hybridization. Molecular analysis of the SRD5A2 gene resulted in the identification of 18 mutations in 11 homozygotes, 6 compound heterozygotes, and 4 inferred compound heterozygotes from 23 families with 5 alpha-reductase deficiency. 6 apparent recurrent mutations were detected in 19 different ethnic backgrounds. In two patients, the catalytic efficiency of the mutant enzymes correlated with the severity of the disease. The high proportion of compound heterozygotes suggests that the carrier frequency of mutations in the 5 alpha-reductase type 2 gene may be higher than previously thought.

Characterization and chromosomal mapping of a human steroid 5α-reductase gene and pseudogene and mapping of the mouse homologue ☆

The enzyme steroid 5 alpha-reductase catalyzes the conversion of testosterone into the more powerful androgen, dihydrotestosterone. We previously described the cloning of rat and human cDNAs that encode steroid 5 alpha-reductase and their expression in oocytes and cultured cells. Here, we report the isolation, characterization, and chromosomal mapping of two human steroid 5 alpha-reductase genes. One gene (symbol SRD5A1) is functional, contains five exons separated by four introns, and maps to the distal short arm of chromosome 5. Two informative restriction fragment length polymorphisms are present in exons 1 and 2 of this gene. A second gene (symbol SRD5AP1) has all of the hallmarks of a processed pseudogene and was mapped to the q24-qter region of the X chromosome. In the mouse, a single steroid 5 alpha-reductase gene (Srd5 alpha-1) is linked to Xmv-13 on chromosome 13.

New insights into the phenotypes of 6q deletions.

Deletions of chromosome 6q are rare. We report 3 new patients with 6q deletions. Case 1 is a male with an interstitial deletion [del(6)(q13q14.2)], hypotonia, speech delays, and minor anomalies. Case 2 is a male with an interstitial deletion [del(6)(q16.2q22.32)] and malformations, including truncus arteriosus and bilateral oligodactyly. Case 3 is a male with a terminal deletion [del(6)(q25.2)] with retinal pits, hydrocephalus, atrioventricular canal, and hydronephrosis. The findings in our patients and those from 57 previously reported cases demonstrated 3 phenotypic groups associated with 6q deletions. Group A [del(6)(q11-q16)] had a high incidence of hernias, upslanting palpebral fissures, and thin lips with lower frequency of microcephaly, micrognathia, and heart malformations. Group B [del(6)(q15-q25)] was associated with increased intrauterine growth retardation, abnormal respiration, hypertelorism, and upper limb malformations. Group C [del(6)(q25-qter)] was associated with retinal abnormalities, cleft palate, and genital hypoplasia. The only universal finding among all patients with 6q deletions was mental retardation. Other findings common to all 3 groups included ear anomalies (90%), hypotonia (82%), and postnatal growth retardation (68%).

Hemizygosity at the insulin-like growth factor I receptor (IGF1R) locus and growth failure in the ring chromosome 15 syndrome

The ring chromosome 15 syndrome is characterized by mild-to-severe growth failure. We evaluated the status of the insulin-like growth factor I receptor (IGF1R) gene, which had previously been assigned to band 15q26 in several patients with de novo ring 15 chromosomes, to investigate a possible correlation between disruption or loss of the IGF1R gene with the severe growth failure phenotype. The presence or absence of the IGF1R gene on the ring 15 chromosomes of five patients was ascertained by in situ hybridization and gene-dosage (Southern) blotting. The location of the breakpoints was determined by typing polymorphic markers from the distal end of the long arm of chromosome 15 in both the probands and their parents. Deletion mapping determined that all breakpoints were distal to D15S100 and that the IGF1R gene is located between D15S107 and D15S87. Three patients who had suffered severe growth failure in early childhood were hemizygous at the IGF1R locus, while one patient with borderline short stature had two copies of the IGF1R gene. The correlation between IGF1R gene dosage and growth retardation demonstrated here in our ring chromosome 15 patients suggests a possible role for heterozygous IGF1R gene mutations or deletions in other cases of unexplained growth failure.

Gene for lymphoid enhancer-binding factor 1 (LEF1) mapped to human chromosome 4 (q23-q25) and mouse chromosome 3 near Egf

LEF-1 is a 54-kDa nuclear protein that is expressed specifically in pre-B and T-cells. It binds to a functionally important site in the T-cell receptor alpha enhancer and contributes to maximal enhancer activity. LEF-1 is a member of a family of regulatory proteins that share homology with the high mobility group protein 1 (HMG1). The location of the LEF1 gene on human and mouse chromosomes was determined by Southern blot analysis of DNA from panels of interspecies somatic cell hybrids using a murine cDNA probe. Human-specific DNA fragments were detected in all somatic cell hybrids that retained the human chromosomal region 4cen-q31.2. Fluorescent in situ hybridization with two biotin-labeled overlapping human genomic cosmids revealed a specific hybridization signal at 4q23-q25. The homologous locus in the mouse was mapped to chromosome 3 by Southern analysis of rodent x mouse hybrid cell DNA. This chromosomal location was confirmed by the use of a restriction fragment length polymorphism (RFLP) in recombinant inbred mouse strains. The results of this RFLP analysis indicated that the mouse Lef-1 gene was closely linked to Pmv-39 and Egf and was likely placed between these loci, both of which were previously mapped to distal mouse chromosome 3. Our mapping results did not suggest involvement of this gene in previously mapped genetic disorders or in known neoplasia-associated translocation breakpoints.

Chromosome localizations of genes for five cAMP-specific phosphodiesterases in man and mouse

Cyclic nucleotides are important second messengers that mediate a number of cellular responses to external signals. Cyclic nucleotide phosphodiesterases play a role in signal transduction by regulating the cellular concentrations of these messengers. Here, we have applied Southern analyses of somatic cell hybrid lines and of recombinant inbred (RI) mouse strains as well as fluorescence chromosomal in situ hybridization (FISH) to chromosomally localize five cAMP-specific nucleotide phosphodiesterase genes in human and mouse. GenesDPDE1, DPDE2, DPDE3, andDPDE4 that share sequence homology with theDrosophila dunce gene were assigned to human chromosomes 19 (DPDE1 andDPDE2), 5q12 (DPDE3), and 1p31 (DPDE4) and to mouse chromosomes 8, 9, 13, and 4, respectively. The high-affinity cAMP-specific phosphodiesterase gene (HCP1) was mapped to human chromosome 8q13-q22. Since these genes are potential candidates for involvement in psychiatric or behavioral disorders, knowledge of their chromosomal localizations will facilitate the discovery of their association with disease genes as they are being mapped by linkage studies.

Gene for a tissue-specific transcriptional activator (EBF or Olf-1), expressed in early B lymphocytes, adipocytes, and olfactory neurons, is located on human Chromosome 5, band q34, and proximal mouse Chromosome 11

Murine B lymphocytes, adipocytes, and olfactory neurons contain a DNA-binding protein that participates in the regulation of genes encoding tissue-specific components of signal transduction. Purification and cloning of this protein, termed early B-cell factor (EBF), from murine B lymphocytes and independent cloning of a protein, termed Olf-1, from olfactory neuronal cells revealed virtual complete amino acid sequence identity between these proteins. As a first step towards identifying a human genetic disorder or mouse mutation for which EBF could be a candidate gene, we have chromosomally mapped the corresponding locus in both species. By Southern hybridization analyses of somatic cell hybrid panels with murine cDNA probe, fluorescence chromosomal in situ hybridization (FISH) of human genomic clones, and analysis of recombinant inbred mouse strains, we have found single sites for EBF homologous sequences on human Chromosome (Chr) 5, band q34, and on proximal mouse Chr 11, in an evolutionarily conserved region.

Tumor necrosis factor receptor genes,TNFR1 andTNFR2, on human chromosomes 12 and 1

Tumor necrosis factor, TNF, is a 17-kDa protein secreted by macrophages and classified as a cytokine. TNF binds to high-affinity receptors on the cell surface and is involved in a wide variety of biological responses. There are at least two types of receptors, tumor necrosis factor receptors 1 and 2 (TNFR1 and TNFR2). The genes for TNFR1, a 55-kDa protein, and TNFR2, a 70-kDa protein, have been mapped to human chromosomes 1 12 (12pter-cen) and (1pter-p32), respectively, by Southern blot analysis of human × Chinese hamster somatic cell hybrid panels. Recently, the corresponding genes in the mouse have been mapped to chromosomes 4 and 6 in regions that are conserved on human chromosomes 1 and 12.

Ullrich-Turner syndrome and neurofibromatosis-1

There is a well-known association between neurofibromatosis-1 (NF1) and Noonan syndrome-like manifestations, including short stature, short broad neck, and hypertelorism. These anomalies are thought to be due to variable expression of the NF1 gene. We report on two girls with NF1 who were found to have the Ullrich-Turner syndrome. Case 1, a 12-year-old white girl, was followed in a Neurofibromatosis Clinic because of multiple café-au-lait spots and a family history of NF1 in her mother and sister. On examination, she had short stature, hypertelorism, and short neck with low posterior hairline. Karyotype was 86% 46,XY/14% 45,X. Case 2, the first child of a woman with NF1, presented at birth with lymphedema of hands and feet and a short broad neck. Karyotype was 45,X. At age 23 months she was short, had epicanthic folds, hypertelorism, narrow palate, right simian crease, 19 café-au-lait spots, and axillary freckling. We conclude that chromosome studies should be performed in girls with NF1 who have short stature and Noonan- or Ullrich-Turner-like findings. Dilemmas raised by the dual diagnoses of NF1 and Ullrich-Turner syndrome include potential risks of growth hormone therapy and estrogen replacement therapy.