The genes for apolipoprotein all (APOA2) and the Duffy blood group (FY) are linked on chromosome 1 in man

We have cloned a cDNA probe for human apolipoprotein AII and used it to analyze linkage relationships on chromosome 1. We found no recombinations between APOA2 and the gene coding for the Duffy blood group antigens (FY) in the 19 meioses examined. Our maximal lod score is 4.2 at zero recombination rate. K. Berg (1987, Cytogenet. Cell Genet. 46:579) found a maximal score of 2.5 at recombination fraction 0.14 in 54 meioses. When results from both studies are combined, the most likely distance between FY and APOA2 is about 10% recombination with a combined lod score of 5.6 for both sexes.     

Expression of human salivary protein genes

Human proline-rich proteins (PRPs) are polymorphic, homologous in sequence, and linked in a cluster called the human salivary protein complex (SPC). Recently this complex was localized to human chromosome band 12p13.2 (Mamulaet al., Cytogenet. Cell Genet. 39:279, 1985). We have isolated a PRP cDNA, EO27, from a human parotid gland library, identified it by DNA sequencing, and used it to study the molecular and cellular biology of PRP production. Cell-free translation and mRNA characterization with EO27 indicate that the numerous PRPs seen in saliva are produced from relatively few, large precursors, probably by posttranslational cleavage. This supports an hypothesis originally proposed by Friedman and Karn in 1977 (Am. J. Hum. Genet. 29:44A;Biochem. Genet. 15:549) and later supported by biochemical studies (Karnet al., Biochem Genet. 17:1061, 1979) and molecular studies (Mamulaet al., Fed. Proc. 43:1522, 1984; Maedaet al., J. Biol. Chem. 260:1123, 1985). EO27 was also used in this study to localize PRP mRNA production to the acinar cells of the parotid gland byin situ hybridization.     

The genes for the highly homologous Ca(2+)-binding proteins oncomodulin and parvalbumin are not linked in the human genome.

The chromosomal loci of the human parvalbumin and oncomodulin single-copy genes that encode structurally and evolutionarily closely related Ca(2+)-binding proteins were determined by somatic cell hybrid analysis. Southern blot analysis of genomic DNA from 25 human-hamster somatic cell hybrids showed that the human gene for oncomodulin resides on chromosome 7. Analysis of human-mouse hybrids selectively retaining human chromosome 7 or a portion of it allowed specific assignment of the gene locus to the p11-p13 region of chromosome 7 known to be mutated or deleted in patients with the Greig cephalopolysyndactyly syndrome. By gene dosage analysis on Southern blots, we showed that the gene for human parvalbumin maps distally to the cat eye syndrome marker D22S9 on chromosome 22q. Using somatic cell hybrids containing parts of human chromosome 22, the parvalbumin gene was sublocalized to the region 22q12-q13.1. This region contains a linkage group that maps to mouse chromosome 15, region E, and includes the SIS, ARSA, and DIA 1 genes. Our findings are consistent with the recent localization of the mouse parvalbumin gene to this region by two independent methods (C. H. Zühlke et al., 1989, Genet. Res. 54:37-43; S. Adolph et al., 1989, Cytogenet. Cell Genet. 52:177-179).     

Physical mapping of the factor VIII gene proximal to two polymorphic DNA probes in human chromosome band Xq28: implications for factor VIII gene segregation analysis

Genomic DNA segments for the coagulation factor VIIIc gene (F8C), which exhibits only limited restriction length polymorphism, map to the proximal region of band Xq28 by somatic cell hybridization analysis and in situ hybridization. Using somatic cell hybrids, we have obtained data which place probes DX13 (used to detect locus DXS15) and St14 (used to detect DXS52) distal to F8C, within band Xq28. Previous studies have mapped the factor IX gene (F9) and probe 52A (used to detect DXS51) proximal to F8C, in Xq26----q27 and Xq27, respectively (Camerino et al., 1984; Drayna et al., 1984; Mattei et al., 1985). Thus, the relative order of genetic marker loci in the Xq27----qter region is most likely cen-F9-DXS51-F8C-(DXS15, DXS52)-Xqter. The collection of these molecular probes is thus potentially useful in three-factor crosses of factor VIII gene segregation.     

Physical mapping of the loci Gabra3, DXPas8, CamL1, and Rsvp in a region of the mouse X chromosome homologous to human Xq28.

Using pulsed-field gel electrophoresis, a 3 million-bp physical map containing the X-linked loci Gabra3, DXPas8, CamL1, and Rsvp has been constructed for a segment of the mouse X chromosome homologous to human Xq28. Detailed mapping was performed using single and double digestions with rare-cutter restriction enzymes. Gabra3 and DXPas8 have been shown to be physically linked within a maximal distance of 1600 kb, DXPas8 and CamL1 within 750 kb, and CamL1 and Rsvp within 450 kb. In addition, several CpG islands have been detected in the region encompassing CamL1 and Rsvp. These studies confirm a gene order of cen-Gabra3-DXPas8-CamL1-Rsvp-tel determined by genetic mapping in interspecific backcrosses (A.S. Ryder-Cook et al., 1988, EMBO J. 7: 3017-3021; G.E. Herman et al., 1991, Genomics 9: 670-677). Physical distances for the loci studied agree with the calculated genetic distances. Assuming that there is conserved linkage between man and mouse in the region, the physical mapping data presented here may help to clarify the uncertain gene order for some human Xq28 loci.     

Human U1 small nuclear RNA pseudogenes do not map to the site of the U1 genes in 1p36 but are clustered in 1q12-q22.

Human U1 small nuclear RNA is encoded by approximately 30 gene copies. All of the U1 genes share several kilobases of essentially perfect flanking homology both upstream and downstream from the U1 coding region, but remarkably, for many U1 genes excellent flanking homology extends at least 24 kilobases upstream and 20 kilobases downstream. Class I U1 RNA pseudogenes are abundant in the human genome. These pseudogenes contain a complete but imperfect U1 coding region and possess extensive flanking homology to the true U1 genes. We mapped four class I pseudogenes by in situ hybridization to the long arm of chromosome 1, bands q12-q22, a region distinct from the site on the distal short arm of chromosome 1 to which the U1 genes have been previously mapped (Lund et al., Mol. Cell. Biol. 3:2211-2220, 1983; Naylor et al., Somat. Cell Mol. Genet. 10:307-313, 1984). We confirmed our in situ hybridization results by genomic blotting experiments with somatic cell hybrid lines with translocation products of human chromosome 1. These experiments provide further evidence that class I U1 pseudogenes and the true U1 genes are not interspersed. The results, along with those published elsewhere (Bernstein et al., Mol. Cell. Biol. 5:2159-2171, 1985), suggest that gene amplification may be responsible for the sequence homogeneity of the human U1 gene family.     

A deletion hot spot in the Duchenne muscular dystrophy gene

We have made a detailed study of a deletion hot spot in the distal half of the Duchenne muscular dystrophy (DMD) gene, using intragenic probe P20 (DXS269), isolated by a hybrid cell-mediated cloning procedure. P20 detects 16% deletions in patients suffering from either DMD or Becker muscular dystrophy (BMD), in sharp contrast to the adjacent intragenic markers JBir (7%) and J66 (less than 1%), mapping respectively 200-320 kb proximal and 380-500 kb distal to P20. Of the P20 deletions, 30% start within a region of 25-40 kb, the majority extending distally. P20 was confirmed to map internal to a distal intron of the DMD gene. This region was recently shown by both cDNA analysis (M. Koenig et al., 1987; Cell 50: 509-517), and field inversion electrophoresis studies (J.T. Den Dunnen et al., 1987, Nature (London) 329: 640-642) to be specifically prone to deletions. In addition, P20 detects MspI and EcoRV RFLPs, informative in 48% of the carrier females. Together, these properties make P20 useful for carrier detection, prenatal diagnosis, and the study of deletion induction in both DMD and BMD.     

Localization of two genes for Usher syndrome type I to chromosome 11.

The Usher syndromes (USH) are autosomal recessive diseases characterized by congenital sensorineural hearing loss and progressive pigmentary retinopathy. While relatively rare in the general population, collectively they account for approximately 6% of the congenitally deaf population. Usher syndrome type II (USH2) has been mapped to chromosome 1q (W. J. Kimberling, M. D. Weston, C. M?ller, et al., 1990, Genomics 7: 245-249; R. A. Lewis, B. Otterud, D. Stauffer, et al., 1990, Genomics 7: 250-256), and one form of Usher syndrome type I (USH1) has been mapped to chromosome 14q (J. Kaplan, S. Gerber, D. Bonneau, J. Rozet, M. Briord, J. Dufier, A. Munnich, and J. Frezal, 1990. Cytogenet. Cell Genet. 58: 1988). These loci have been excluded as regions of USH genes in our data set, which is composed of 8 French-Acadian USH1 families and 11 British USH1 families. Both of these sets of families show linkage to loci on chromosome 11. Linkage analysis demonstrates locus heterogeneity between these sets of families, with the French-Acadian families showing linkage to D11S419 (Z = 4.20, theta = 0) and the British families showing linkage to D11S527 (Z = 6.03, theta = 0). Genetic heterogeneity of the data set was confirmed using HOMOG and the M test (log likelihood ratio > 10(5)). These results confirm the presence of two distinct USH1 loci on chromosome 11.     

Diagnosis of genetic disease using recombinant DNA. Third edition

Summary Recombinant DNA methodology has greatly increased our knowledge of the molecular pathology of the human genome at the same time as providing the means to diagnose inherited disease at the DNA level. Direct detection and analysis of a range of genetic defects are now possible using cloned gene or oligonucleotide probes or by direct sequencing of the disease gene(s). In addition, the use of restriction fragment length polymorphisms (RFLPs) within and around these genes as indirect genetic markers has now potentiated the tracking of disease alleles in affected pedigrees in cases where direct analysis was not feasible. RFLPs associated with linked anonymous segments may also be used not only to diagnose hitherto undetectable disease states, but also for chromosomal localization of the loci responsible. We present here an updated list of reports describing both the direct and the indirect analysis/diagnosis of human inherited disease; it is intended to serve as a guide to current molecular genetic approaches in diagnostic medicine.Abbreviations ADG Annales de Genetique - AHG Ann. Hum. Genet. - AICHG Abstracts Int. Congress Hum. Genet. 7, Berlin, 1986 - AJH Am. J. Haematol. - AJHG Am. J. Hum. Genet. - AJMG Am. J. Med. Genet. - AN Aneuploidy - ANYAS Ann. New York Acad. Sci - APRT Adeninephosphoribosyltransferase - ASHG American Soc. Hum. Genet. Abstracts 34th Ann. Meeting - ATS VII Atherosclerosis VII, Eds. Fidge and Nestel, Elsevier - Arch. Neurol. Archieves of Neurology - Arch. Oph. Arch. Ophthalmol. - Atherosclr. Atherosclerosis - BBRC Biochim. Biophys. Res. Comm. - BJH Brit. J. Haematol. - BMJ Brit. Med. J. - BST Biochem. Soc. Transact. - CCG Cytogenet. Cell Genet. - CDC Carrier detection using clonality - CGC Cancer Genet. Cytogenet. - DEL Deletion - DETECT Mode of Detection - Dis. Marker Disease Markers - DUP Duplication - EJB Eur. J. Biochem. - EJI Eur. J. Immunol. - HGM8 Human Gene Mapping 8 (CCG, Vol. 40, 1–824, 1985) - HGM9 Human Gene Mapping 9 (CCG, Vol. 46, 1–824, 1987) - HGM10 Human Gene Mapping 10 (CCG, Vol. 51, 1–824, 1989) - HPRT Hypoxanthinephosphoibosyltransferase - HVR Hypervariable region - Hos. Prac. Hospital Practice - IMG Immunogenetics - INS Insertion - INV Inversion - IZ Inter-zeta - J. Mol. End. J. Molec. Endocrinol. - JAMA J. Amer. Med. Assoc. - JBC J. Biol. Chem. - JCB J. Cell. Biol. - JCEM J. Clin. Endocrinol. Metab. - JCI J. Clin. Invest. - JMD J. Inher. Metab. Dis. - JIMM J. Immunogenet. - JJCR Jpn. J. Cancer Res. - JJHG Jpn. J. Hum. Genet. - JMG J. Med.Genet. - JNR J. Neurosci. Res. - LH Loss of heterozygosity - MBM Mol. Biol. Med. - MCB Molec. Cell. Biol. - MCKUS McKusick catalogue number - MMP Mismatch pairing analysis - MODY Maturity onset diabetes of the young - MOL. END. Molec. Endocrinol. - MUT Mutation - NAR Nucl. Acids Res. - NEJM New Engl. J. Med. - Neurol. Sup. Neurology Supplement - OLIGO Detection of mutation by oligonucleotide hybridisation - OPG Ophthal. Pediatr. Genet. - PNAS Proc. Natl. Acad. Sci. USA - Ped. Res. Pediatric Res. - PM Point mutation - Pren. Diag. Prenatal Diagnosis - RE Restriction enzyme analysis - REAR Rearrangement - RFLP Indirect analysis using likned RFLP - SEQU Analysis by DNA sequencing - SCMG Somat. Cell Molec. Genet. - Thr. Res. Thrombosis Research - XIA X-inactivation analysis - ar alphoid repeat - atyp. atypical - breakp. breakpoint - def. deficiency - fruct. fructose - haem. haemoglobin - hered. hereditary - minisat. minisatellite - mt mitochondrial - neph. nephritis - persist. persistent - phosph. phosphorylase - resis. resistant - phosph. phosphorylase - resist. resistant - sev. several - synth. synthetase - var various     

Combining thermostable mutations increases the stability of lambda repressor

We have combined three mutations previously shown to stabilize lambda repressor against thermal denaturation. Two of these mutations are in helix 3, where Gly-46 and Gly-48 have been replaced by alanines [Hecht, M. H., et al. (1986) Proteins: Struct., Funct., Genet. 1, 43-46]. The other mutation, which replaces Tyr-88 with cysteine, allows the protein to form an intersubunit disulfide bond [Sauer, R. T., et al. (1986) Biochemistry 25, 5992-5998]. Calorimetric measurements show that the two alanine substitutions stabilize repressor by about 8 degrees C, that the disulfide bond stabilizes repressor by about 8 degrees C, and that the triple mutant is 16 degrees C more stable than wild-type repressor.     

Disruption of genes encoding predicted inner arm dynein heavy chains causes motility phenotypes in Tetrahymena

The multi-dynein hypothesis [Asai, 1995: Cell Motil Cytoskeleton 32:129-132] states: (1) there are many different dynein HC isoforms; (2) each isoform is encoded by a different gene; (3) different isoforms have different functions. Many studies provide evidence in support of the first two statements [Piperno et al., 1990: J Cell Biol 110:379-389; Kagami and Kamiya, 1992: J Cell Sci 103:653-664; Gibbons, 1995: Cell Motil Cytoskeleton 32:136-144; Porter et al., 1996: Genetics 144:569-585; Xu et al., 1999: J Eukaryot Microbiol 46:606-611] and there is evidence that outer arms and inner arms play different roles in flagellar beating [Brokaw and Kamiya, 1987: Cell Motil. Cytoskeleton 8:68-75]. However, there are few studies rigorously testing in vivo whether inner arm dyneins, especially the 1-headed inner arm dyneins, play unique roles. This study tested the third tenet of the multi-dynein hypothesis by introducing mutations into three inner arm dynein HC genes (DYH8, 9 and 12) that are thought to encode HCs associated with 1-headed inner arm dyneins. Southern blots, Northern blots, and RT-PCR analyses indicate that all three mutants (KO-8, 9, and 12) are complete knockouts. Each mutant swims slower than the wild-type cells. The beat frequency of KO-8 cells is lower than that of the wild-type cells while the beat frequencies of KO-9 and KO-12 are not different from that of wild-type cells. Our results suggest that each inner arm dynein HC is essential for normal cell motility and cannot be replaced functionally by other dynein HCs and that not all of the 1-headed inner arm dyneins play the same role in ciliary motility. Thus, the results of our study support the multi-dynein hypothesis [Asai, 1995: Cell Motil Cytoskeleton 32:129-132].     

X-linked nephrogenic diabetes insipidus: From the ship hopewell to RFLP studies

Nephrogenic diabetes insipidus (NDI; designated 304800 in Mendelian Inheritance in Man) is an X-linked disorder with abnormal renal and extrarenal V2 vasopressin receptor responses. The mutant gene has been mapped to Xq28 by analysis of RFLPs, and tight linkage between DXS52 and NDI has been reported. In 1969, Bode and Crawford proposed, under the term "the Hopewell hypothesis," that most cases in North America could be traced to descendants of Ulster Scots who arrived in Nova Scotia in 1761 on the ship Hopewell. They also suggested a link between this family and a large Mormon pedigree. DNA samples obtained from 13 independent affected families, including 42 members of the Hopewell and Mormon pedigrees, were analyzed with probes in the Xq28 region. Genealogical reconstructions were performed. Linkage between NDI and DXS304 (probe U6:2.spl), DXS305 (St35-691), DXS52 (St14-1), DXS15 (DX13), and F8C (F814) showed no recombination in 12 families, with a maximum lod score of 13.5 for DXS52. A recombinant between NDI and DXS304, DXS305, was identified in one family. The haplotype segregating with the disease in the Hopewell pedigree was not shared by other North American families. PCR analysis of the St14 VNTR allowed the distinction of two alleles that were not distinguishable by Southern analysis. Carrier status was predicted in 24 of 26 at-risk females. The Hopewell hypothesis cannot explain the origin of NDI in many of the North American families, since they have no apparent relationship with the Hopewell early settlers, either by haplotype or by genealogical analysis. We confirm the locus homogeneity of the disease by linkage analysis in ethnically diverse families. PCR analysis of the DXS52 VNTR in NDI families is very useful for carrier testing and presymptomatic diagnosis, which can prevent the first manifestations of dehydration.     

A cell-specific enhancer of the mouse alpha 1-antitrypsin gene has multiple functional regions and corresponding protein-binding sites.

We have previously described the isolation and characterization of genomic clones corresponding to the mouse alpha 1-antitrypsin gene (Krauter et al., DNA 5:29-36, 1986). In this report, we have analyzed the DNA sequences upstream of the RNA start site that direct hepatoma cell-specific expression of this gene when incorporated into recombinant plasmids. The 160 nucleotides 5' to the cap site direct low-level expression in hepatoma cells, and sequences between -520 and -160 bp upstream of the RNA start site functioned as a cell-specific enhancer of expression both with the alpha 1-antitrypsin promoter and when combined with a functional beta-globin promoter. Within the enhancer region, three binding sites for proteins present in hepatoma nuclear extracts were identified. The location of each site was positioned, using both methylation protection and methylation interference experiments. Each protein-binding site correlated with a functionally important region necessary for full enhancer activity. These experiments demonstrated a complex arrangement of regulatory elements comprising the alpha 1-antitrypsin enhancer. Significant qualitative differences exist between the findings presented here and the cis-acting elements operative in regulating expression of the human alpha 1-antitrypsin gene (Ciliberto et al., Cell 41:531-540, 1985; De Simone et al., EMBO J. 6:2759-2766, 1987).     

New Phytologist 140 (1998), 363–383

In the November 1998 issue of New Phytologist , we published the Tansley review 'Gibberellins: regulating genes and germination' by Sian Ritchie and Simon Gilroy ( New Phytol. (1998) 140 , 363–383). Since its publication, it has come to our attention that text associated with Fig. 4 was omitted during production. The correct figure is reprinted here in full.
We apologise to the author and to our readers for this mistake.
Figure 4. Promoter sequences of various genes expressed in the cereal aleurone and shown to be regulated by GA. The position of each sequence is indicated relative to the start codon. Regions identified as being involved in regulation of the genes are highlighted, as are similar regions in other genes. Sites at which protein has been shown to bind are also indicated. ( a ) Barley Amy 32b (Sutcliff et al ., 1993; Whittier et al ., 1987); wheat Amy 2/54 (Huttley et al ., 1992; Rushton et al ., 1992; Rushton et al ., 1995); barley Amy 46 (Khursheed & Rogers, 1988); barley Amy 2/p155 (Knox et al ., 1987); barley aleurain (Whittier et al ., 1987); barley β-glucanase II (Wolf, 1992); wheat cathepsin B-like (Cejudo et al ., 1992); rice ubiquitin-conjugating enzyme (Chen et al ., 1995). ( b ). Wheat Amy 1/18 (Rushton et al ., 1992); barley Amy pHV 19 (Jacobsen & Close, 1991; Gubler & Jacobsen, 1992)/ Amy 1 / 6-4 (Khursheed & Rogers, 1988; Rogers, Lanahan & Rogers 1994); rice OSamy-a / Amy 3c (Ou-Lee et al ., 1988; Sutcliff et al ., 1991; Yu et al ., 1992; Goldman et al ., 1994); rice Amy 3B (Sutcliffe et al ., 1991); rice OSamy-c (Kim et al ., 1992; Kim & Wu, 1992; Tanida et al ., 1994); rice Amy 1A (Huang et al ., 1990; Itoh et al ., 1995).
Figure 4 ( b ). For legend see facing page.     

Comparative mapping of the oat <Emphasis Type="Italic">Dw6/dw6</Emphasis> dwarfing locus using NILs and association with vacuolar proton ATPase subunit H

Seven pairs of oat near-isogenic lines (NILs) (Kibite in Crop Sci 41:277–278, 2001) contrasting for the Dw6 dwarfing gene were used to test for correlation between tall/dwarf phenotype and polymorphic genotype using restriction fragment length polymorphism (RFLP) and other molecular markers selected from the Kanota × Ogle (K×O) (Wight et al. in Genome 46:28–47, 2003) and Terra × Marion (De Koeyer et al. in Theor Appl Genet 108:1285–1298, 2004) recombination maps. This strategy located the Dw6/dw6 locus to a small chromosomal region on K×O linkage group (LG) KO33, near or at a putative RFLP locus aco245z. Aco245z and other tightly linked flanking markers have potential for use in marker-assisted selection (MAS), and PCR-based markers were developed from several of these. RFLP genotyping of the Dw6 NILs indicated that 13 of the 14 individual lines were homogeneously maternal or paternal for a large genomic region near Dw6/dw6, an unexpected result for NILs. The cDNA clone aco245 codes for a vacuolar proton ATPase subunit H, a potential candidate gene for Dw6. Vacuolar proton ATPase enzymes have a central role in plant growth and development and a mutation in subunit C is responsible for the det3 dwarfing mutation in Arabidopsis thaliana (Schumacher et al. in Genes Dev 13:3259–3270, 1999). Aco245 affords the potential of designing highly precise diagnostic markers for MAS for Dw6. The Dw6 NILs have potential utility to investigate the role of vacuolar proton ATPases in growth and development in plants.     

Sequence similarities among monkey ori-enriched (ors) fragments

Nucleotide sequences have been determined for eight ors (ori-enriched sequence) fragments isolated from monkey DNA by a method that was designed to enrich for origins of DNA replication [Kaufmann et al., Mol. Cell. Biol. 5 (1985) 721-727]. Evidence has been presented that some or possibly all of these sequences can serve, albeit inefficiently, as oris in vivo [Frappier and Zannis-Hadjopoulos, Proc. Natl. Acad. Sci. USA 84 (1987) 6668-6672]. Two of the fragments were found to contain the long terminal repeat-like elements of the 'O-family' of moderately repetitive sequences that are present in human DNA as a transposon-like element [Paulson et al., Nature 315 (1985) 359-361]. Extensive pair-wise comparisons of the sequences failed to detect any statistically significant common sequences, except for long asymmetrically distributed A + T-rich stretches. Nonetheless, when the ors fragments were examined for the presence of published consensus sequences, seven of eight were found to contain the control sequence described by Dierks et al. [Cell 32 (1983) 695-706], and the same seven of eight were found to contain both the scaffold attachment region T consensus [Gasser and Laemmli, Cell 46 (1986) 521-530] and the minimal Saccharomyces cerevisiae autonomously replicating sequence consensus [e.g., Palzkill and Newlon, Cell 53 (1988) 441-450].     

The Gene for Hereditary Bullous Dystrophy, X-Linked Macular Type, Maps to the Xq27.3-qter Region

Bullous dystrophy, hereditary macular type (McKusick 302000), is an X-linked disorder and was originally described in a single kindred in the Netherlands by Mendes da Costa and Van der Valk in 1908. To determine the location of the bullous dystrophy gene, segregation studies were performed in this family and in a recently described Italian family. Using informative polymorphic markers, the gene could initially be localized on the Xq27-q28 region. No recombinants were noted with loci in Xq27.3-q28. Fine mapping places the bullous dystrophy locus distal to DXS102 (Xq26.3) in the Italian family and distal to DXS998 (Xq27.3) in the Dutch family.     

Basic defect in the expression of adenosine deaminase in ADA- SCID disease investigated through the cells of an obligate heterozygote

Summary The nature of the defect of a female baby who died of severe combined immunodeficiency (SCID) disease associated with adenosine deaminase deficiency (ADA^-) was investigated. Since tissue or tissue culture material was not available for subsequent studies, the expression of ADA in her cells was investigated in the somatic cell hybrid clones derived from a fusion between the lymphocytes from one of her two obligate heterozygote parents and thymidine kinase deficient Chinese hamster (a3) fibroblasts. The results of analyses of the human chromosomes and biochemical markers in 12 independent clones and 27 subclones indicated that the ADA deficiency in the patient is determined probably by a mutation in the structural gene for ADA in chromosome 20 leading either to the production of catalytically defective molecules or to the cessation of the production of ADA. Incidentally, the involvement of chromosome 2, which carries a gene for adenosine deaminase complexing protein (ADCP), in the causation of ADA deficiency was excluded. The in vitro approach through the cells from an obligate heterozygote described in this paper may have a general application in pursuing studies on other cases of inborn errors of metabolism whenever the material from the affected individuals (i.e., the homozygotes) is not available or not suitable for direct investigations.A part of this work was presented at the New York State Department of Health, Birth Defects Institute Symposium IX (Inborn Errors of Specific Immunity), Albany, October 16–18, 1978 and reported as an abstract in the proceedings of the Fifth International Conference on Human Gene Mapping, Edinburgh, July 1979. Cytogenet Cell Genet 22:164