Multiple giant molluscum contagiosa with cyst formation

We report a case of multiple cystic tumors distributed on the scalp, face, neck, and upper trunk of a 68-year-old male. In all five cysts examined, the presence of molluscum contagiosum virus (MCV) was demonstrated electron microscopically, and the typical histological features of MCV infection were observed in the cyst wall. In one lesion, histological features suggesting a follicular origin of the cyst were seen.

Isolation of a human allo-peptide presented by HLA-B51 molecules

Recent studies have demonstrated directly that alloreactive mouse CTL recognize peptides presented by MHC class I molecules. However, there is no direct evidence that human alloreactive CTL recognize peptides presented by HLA class I molecules. We have isolated an HLA-B51 alloreactive CTL clone, 2B3, that did not kill the TAP defective cell lines T2 and .174, whereas it killed the TAP-positive cell line T1 and .174 cells transfected with TAP genes. These findings suggested that this clone recognizes a TAP-dependent allo-peptide. We attempted to isolate the human allo-peptide recognized by the 2B3 clone from HLA-B51 molecules. A naturally occurring HLA-B*5101 binding peptide isolated from T1 cells was recognized by the 2B3 clone. The peptide was also isolated from HLA-B*5101 molecules purified from C1R-B*5101 cells. In the present study, we directly demonstrated that a human alloreactive CTL clone recognizes peptide presented by HLA class I molecules.

Suppression of cytotoxic T lymphocyte activity by gamma/delta T cells in tumor-bearing mice

Spleen cells derived from tumor-bearing mice prove useful for the elucidation of the mechanism determining how tumor cells evade cytotoxic T lymphocytes (CTL) in tumor-bearing hosts. Our data indicate that inactive CTL or precursor CTL specific for tumor antigens are present among lymphocytes of tumor-bearing mice. However, their activity is inhibited by a soluble factor produced by other cells present in the same source. Inhibition of the cytolytic reaction was also detected in the culture supernatant of spleen cells obtained from normal mice, precultured in the presence of tumor cell culture supernatant and interleukin-2 (IL-2). Cell-depletion and cell-purification studies let us conclude that cells that produced the CTL-inhibitory factor (CTL-IF) were gamma/delta T cells. The gamma/delta T cells that were activated in vivo in tumor bearers were able to produce CTL-IF after isolation and in vitro culture. Maximum activation of gamma/delta T cells was achieved by antigenic stimulation and by suppression of cells that interfered with the activation of gamma/delta T cells. CTL-IF, which was assayed by use of CTL clones, did not show antigen specificity. Inhibition depended on a relatively heat- and acid-stable, but alkali-labile molecule with a molecular mass of less than 10 kDa. The latter characteristics imply that CTL-IF does not resemble any of the known lymphokines produced by gamma/delta T cells. These observations emphasize the crucial role of the gamma/delta T cells in the escape of tumor cells from the attack of tumor-specific CTL.

Detection of human papillomaviruses and eccrine ducts in palmoplantar epidermoid cysts

Although epidermoid cysts of the palms and soles have long been assumed to develop following implantation of an epidermal fragment as a result of a penetrating injury, the pathogenic mechanism is still controversial, and the discovery of a more common aetiological agent is awaited. Clinical, histological, immunohistochemical and molecular biological studies were performed on 119 epidermoid cysts of palmoplantar location, in order to examine the role of the eccrine ducts, and human papillomavirus (HPV), in the pathogenesis of this disorder. Characteristic histological features were found, including intracytoplasmic eosinophilic bodies (ICB: in 14 cases, 12%) in the cyst wall, vacuolar structures (V: in 28 cases, 24%), or parakeratotic nuclei (P: in 85 cases, 71%) within the keratinous mass in the cyst cavity. Ductal structures suggesting eccrine ducts (E: in 63 cases, 53%) were also found in the cyst wall or in the cyst cavity. Either ductal structures or carcinoembryonic antigen expression (66 cases, 55%) were noted in a total of 73 cases (61%). Papillomavirus common antigens were detected in 36 cases (30%) showing one or more of the three distinct histological features, i.e. ICB, V and P. Subsequently, hybridization experiments to detect HPV DNA were performed in 47 cases, revealing an association between cysts showing ICB or V and the presence of HPV 60 DNA sequences. On the basis of our results, we propose that epidermoid cysts in the palmoplantar regions may develop from eccrine ducts, and that HPV and injury may play a role in their pathogenesis.

Amplification and analysis of promoter region of insulin receptor gene in a patient with leprechaunism associated with severe insulin resistance

A patient with leprechaunism associated with severe insulin resistance was studied to identify the molecular and genetic basis for insulin resistance. Insulin binding and surface labeling of transformed lymphocytes prepared from the patient showed a significantly decreased insulin receptor number on the cell surface. Southern blot analysis of the insulin receptor gene showed no evidence of large insertions or deletions. Furthermore, direct sequencing of all 22 exons and exon-intron junctions of the insulin receptor gene failed to show any missense mutations, nonsense mutations, or mutations at exon-intron junctions. However, Northern blot analysis indicated significantly decreased insulin receptor mRNA expression in the patient's cells. Moreover, restriction endonuclease digestion of the amplified cDNA suggested that the expression levels of one allele were less efficient than the other. These findings suggested that the regulatory region of the insulin receptor gene might have abnormalities. Therefore, we examined the 5' flanking region of the insulin receptor gene. Southern blot analysis showed no major deletions or insertions between positions -1,823 and -2 relative to the translation initiation site. A 5' flanking region of the insulin receptor gene spanning positions -881 approximately +7 was amplified by polymerase chain reaction (PCR) and introduced into a reporter plasmid carrying the human growth hormone (hGH) gene. The nucleotide sequence of the amplified fragment showed two polymorphic sites at positions -603 and -500 in the patient, as well as in normal subjects. No other abnormal sequence was found in the patient. Promoter activity measured by hGH expression in transfected mouse L cells was not influenced by the polymorphism at position -603 located in a cluster of GC boxes.(ABSTRACT TRUNCATED AT 250 WORDS)

Thiazolidine derivatives ameliorate high glucose-induced insulin resistance via the normalization of protein-tyrosine phosphatase activities

The mechanisms for the insulin resistance induced by hyperglycemia were investigated by studying the effect of high glucose concentration (HG) and its modulation by thiazolidine derivatives, on insulin signaling using Rat 1 fibroblasts expressing human insulin receptors (HIRc). Incubating HIRc cells in 27 mM D-glucose for 4 days impaired the insulin-stimulated phosphorylation of pp185 and receptor beta-subunits. Both protein kinase C activities and phorbol dibutyrate binding to intact cells were unchanged; however, cytosolic protein-tyrosine phosphatase (PTPase) activity increased within 1 h prior to the impairment of insulin receptor kinase in HG cells (Maegawa, H., Tachikawa-Ide, R., Ugi, S., Iwanishi, M., Egawa, K., Kikkawa, R., Shigeta, Y., and Kashiwagi, A. (1993) Biochem. Biophys. Res. Commun. 197, 1078-1082). Increased PTPase activity was consistent with a 2-fold increase in the amount of PTP1B, and anti-PTP1B antibody inhibited this increment of cytosolic PTPase activity in HG cells. Co-incubating cells with pioglitazone prevented these abnormalities in cytosolic PTPase, the PTP1B content and the impaired phosphorylation of pp185 and receptor beta subunits in HG cells. Finally, HG cells had impaired insulin-stimulated alpha-amino-isobutyric acid uptake, which was ameliorated by exposure to thiazolidine derivatives. In conclusion, exposing cells to high glucose levels desensitizes insulin receptor function, and thiazolidine derivatives can reverse the process via the normalization of cytosolic PTPase, but not of protein kinase C.

Epidermoid cyst with sweat ducts on the torso

We report a case of an epidermoid cyst arising on the upper chest that had a remarkable histologic pattern composed of structures resembling eccrine ducts in the horny layer and an acrosyringium. The expression of carcinoembryonic antigen (CEA) was also demonstrated immunohistochemically within these ductal structures. Eccrine ducts have been reported recently, in epidermoid cysts located in the palmoplantar region. The cyst described here suggests that epidermoid cysts derived from eccrine ducts may also appear on the torso.

Effect of radical scavengers on TNF alpha-mediated activation of the uPA in cultured cells

Active oxygen, produced by cultured cells following stimulation with various growth factors, seems to be involved in signal transduction leading to cellular responses such as gene expression and growth modulation. In the present study, the intracellular oxidation state was measured in immortalized human endothelial cells (ECV304) after treatment with tumor necrosis factor (TNF) alpha, using a fluorescent dye and a laser-scanning confocal microscope. The intracellular oxidation state was increased 60 min after the addition of TNF alpha, and this increase was abolished by a radical scavenger, N-acetylcysteine (NAC), which is also a precursor of glutathione, and by pyrrolidine dithiocarbamate (PDTC). TNF alpha increased the steady state level of urokinase-type plasminogen activator (uPA), and NAC inhibited this increase at a dose that also inhibited the increase in the intracellular oxidation state. PDTC, on the other hand, did not affect the induction of the uPA gene by TNF alpha. These results suggest that intracellular glutathione level rather than the oxidation state is necessary for the induction of the uPA gene by TNF alpha.

Spectral analysis of electromyogram in lumbar muscles: fatigue induced endurance contraction

In the last few years, epidemiological studies have shown correlations between the low endurance capacity of the erector spinae muscle and low back pain (LBP). In this study, the function of the erector spinae muscle and localized muscle fatigue in LBP were investigated in both LBP patients and control subjects without LBP, using surface multi-channel electromyograms (EMG). Four positions (L1, L2, L4, L5) were chosen as representative locations for the different functions of the erector spinae muscle. Median frequency (fm) parameters of an EMG power density spectrum were monitored to quantify localized muscle fatigue. This research indicated a statistically significant difference (P < 0.05) in fm parameters between the LBP patients and the control subjects. The integrated electromyogram (iEMG) signals of LBP patients were considerably higher than for the control subjects during endurance isometric contraction. Our research suggested that human fatiguing erector spinae muscle, in submaximal voluntary contractions tests, induced a different firing order of motor unit spikes between two groups.

Leu 193 mutation in the cysteine rich region of the insulin receptor inhibits the cleavage of the insulin receptor precursor but not insulin binding

To characterize the Leu 193 mutant insulin receptor, which was found in a patient with extreme insulin resistance, the mutant insulin receptor was overexpressed in Rat-1 fibroblasts by transfection of mutated insulin receptor cDNA. In the pulse-chase experiment, the cleavage of the proreceptors to the matured receptor subunits was impaired in the cells expressing Leu 193 insulin receptor and therefore, the mutant proreceptors were accumulated in the cell. Insulin bound to the Leu 193 insulin receptor on the cell surface with normal affinity, although the mutation was in the alpha-subunit of the insulin receptor. Therefore, the Leu 193 mutation impaired proreceptor cleavage but not insulin binding.

Utilization of leucine methyl ester for the generation of hybridomas producing monoclonal antibodies specific to tumor-associated antigens

In an attempt to obtain monoclonal antibodies specific to tumor-associated antigens, C3H/He mice were immunized with syngeneic MM2 tumor cells, and the primed spleen cells were fused with P3-X63-Ag8.653 myeloma cells. The outgrowth of hybridomas, however, was extremely low and monoclonal antibodies were not obtained. The reason for the low hybridoma growth was studied. It was found that MM2 cells used as the immunogen, the fusion partner myeloma cells and the resulting hybridomas shared at least one tumor-associated antigen, namely Q5 antigen. Because of this common antigen, cytotoxic cells, presumably cytotoxic T lymphocytes, which were lytic to the hybridomas, were induced during the culture for generation of the hybridomas. Removal of lysosome-rich cells, including cytotoxic T lymphocytes, from the primed spleen cells before the fusion by treatment with leucine methyl ester, a lysosomotropic agent, drastically improved the outgrowth of hybridomas. By this method, seven stable hybridoma clones producing monoclonal antibodies specific to tumor-associated antigens were obtained. Two of the seven clones were found to secrete monoclonal IgM species, which reacted with the extra-cellular region of the Q5 antigen. This procedure will be an option when production of monoclonal antibodies specific to cell-surface antigens is intended and outgrowth of hybridomas is unexpectedly low.

HLA-B*3501-peptide interactions: role of anchor residues of peptides in their binding to HLA-B*3501 molecules

Two HLA-B*3501 binding self-peptides, LPFDFTPGY (37F) and LPGPKFLQY (28H), were isolated from HLA-B*3501 molecules expressed by cultured human B lymphoid cells. Both sequences were consistent with previously reported motifs of HLA-B*3501 binding peptides which carry proline at position 2 and tyrosine at position 9 as anchor residues. Direct binding of these peptides to HLA-B*3501 molecules was quantitated by flow cytometry analysis of RMA-S cells. transfected with the HLA-B*3501 gene (RMA-S-B*3501). Both 37F and 28H peptides bound effectively to HLA-B*3501 molecules. Substitution of amino acids at position 2 and/or 9 of HLA-B*3501 binding peptides markedly reduced their binding to HLA-B*3501 molecules. These results indicate that two anchor residues, proline at position 2 and tyrosine at position 9 are critical in binding of peptides to HLA-B*3501 molecules. Insertion of up to four glycine residues at position 8 of the peptide 37F did not affect its binding affinity to HLA*3501 molecules. These results indicate that long peptides can effectively bind to HLA class I molecules provided that anchor residues are conserved.

New types of human papillomaviruses and intracytoplasmic inclusion bodies: a classification of inclusion warts according to clinical features, histology and associated HPV types

Two new types of intracytoplasmic inclusion bodies (ICBs) associated with distinct clinical features, and the presence of DNA of distinct types of human papillomaviruses (HPVs) are reported. One hundred and seven cutaneous warts containing ICBs were grouped into three categories according to distinct clinicopathological features: 67 were wart lesions with well-known granular (Gr)-ICB, 13 were punctate keratotic lesions with filamentous (Fl)-ICB and 31 were pigmented warts with homogeneous (Hg)-ICB. Molecular biological studies were performed in order to assess a specific association of each group of warts with distinct types of HPV. HPV-1 DNA sequences were detected in all the lesions with a Gr-ICB. Punctate keratotic lesions with Fl-ICB were associated with HPV-63, which was newly cloned from such a lesion. One of the samples also contained HPV-1 DNA. Pigmented warts with Hg-ICBs contained one of the related HPVs, i.e. HPV-4, HPV-60 or a novel type of HPV, HPV-65. Based on these associations, a classification of inclusion warts is proposed.

Pioglitazone ameliorates high glucose induced desensitization of insulin receptor kinase in Rat 1 fibroblasts in culture

A new oral agent, pioglitazone, increases insulin sensitivity by activating receptor kinase in insulin-resistant rats. To clarify the mechanism, we studied in vitro effects of glucose and pioglitazone on the insulin receptor function using Rat 1 fibroblasts which expressed human insulin receptors. Insulin receptor kinase activity was impaired by incubating cells for 4 days in the presence of 27mM D-glucose. The glucose effect was time- and dose-dependent and also specific for D-glucose, since D-raffinose incubation had no effect. Pioglitazone treatment did not have any effect on intact receptor kinase. However, exposure of both 27mM D-glucose and 0.1 microM pioglitazone to the cells completely prevented the glucose-induced impairment of insulin receptor kinase activity, suggesting that pioglitazone might reverse the processes which are critical for the glucose-induced desensitization of insulin receptor kinase.

Co-expression of mutant and normal human insulin receptors in COS 7 cells

In order to assess the interference of the mutant insulin proreceptor on normal receptor function and formation of proreceptor-receptor heterotrimers (alpha beta-proreceptor), COS 7 cells were transfected with the same amount of expression plasmid (pGEM3SV) containing wild-type, a mutant proreceptor cDNA and both, using the DEAE-dextran method. Scatchard analysis of insulin binding data revealed that there was an approx. 50-fold higher receptor concentration in the transfected cells than in untransfected cells. After 0.025% trypsin treatment, insulin binding to the cells expressed with wild-type, proreceptor and both increased by 1-fold, 2.9-fold and 1.5-fold of the untreated cells, respectively. In the presence of 167 nM insulin, the amounts of phosphate incorporated into the 95 kDa protein beta-subunits and 210 kDa proreceptors from co-transfected cells, were identical to those of an in vitro mixture of the wild-type and the mutant receptors. At 10 nM insulin, the proreceptors from co-transfected cells normally autophosphorylated by insulin stimulation, whereas those mixed in vitro did not (73.3 +/- 9.3 vs. 29.6 +/- 2.6% of the maximal effect, n = 4, P < 0.01). However, at a similar concentration of insulin, the phosphate incorporation into Glu-80/Tyr-20 polymers by receptors from co-transfected cells was decreased when compared with a in vitro mixture (9.0 +/- 2.6 vs. 22.5 +/- 6.7% of the maximal effect at 4 nM, n = 6, P < 0.01), although the basal and maximally stimulated phosphate incorporation were comparable among these groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Ala1048-->Asp mutation in the kinase domain of insulin receptor causes defective kinase activity and insulin resistance

We identified a heterozygous missense mutation that substituted aspartic acid (GAC) for alanine (GCC) at codon 1048 of the insulin receptor gene in a patient who displayed typical symptoms of Type A syndrome of insulin resistance. The proband's mother and younger brother were also found to be heterozygous for the mutation. We constructed the identified mutant insulin receptor cDNA by site-directed mutagenesis, transfected the mutant cDNA into COS 7 cells, and found that kinase activity of the mutant insulin receptors was markedly impaired. Ala1048 is located in the kinase domain of the insulin receptor beta-subunit and is conserved in most of protein-tyrosine kinases. Besides, neighboring Glu1047 is invariant in all protein kinases and is thought to be involved in interaction with ATP. Photoaffinity labeling of the mutant insulin receptor with ATP analogue, 8-azido (alpha-32P)ATP was not influenced by the mutation, suggesting that the mutation did not inhibit ATP binding but possibly interfered with subsequent phosphoryl transfer. Insulin-stimulated phosphorylation of exogenous substrate by partially purified insulin receptors prepared from COS 7 cells that were cotransfected with wild-type and mutant insulin receptor cDNAs was markedly impaired, whereas autophosphorylation was decreased by approximately 50% of wild-type receptors. These results indicated that the identified heterozygous substitution of Asp for Ala1048 in insulin receptor was responsible for insulin resistance of this patient.

Double infection with human papillomavirus 1 and human papillomavirus 63 in single cells of a lesion displaying only an human papillomavirus 63-induced cytopathogenic effect

BACKGROUND

Specific histologic features are associated with the presence of certain human papillomaviruses (HPV) in verrucous lesions of the skin. HPV 1 is known to be associated with eosinophilic keratohyalin-like intracytoplasmic inclusion bodies, granular in appearance, whereas the recently described HPV 63 seems to induce inclusion bodies displaying a filamentous structure. Although an infection by two distinct HPV types within a single cell has not been previously reported, we have recently treated a plantar punctate keratotic wart in which only the histologic features seen in an HPV 63-induced lesion were seen, in spite of the detection of double infection of both HPV 1 and HPV 63 DNAs, thus posing the question as to the role of the HPV 1 present in the lesion.

EXPERIMENTAL DESIGN

To localize the genomes of these two viruses within the lesion, double fluorescence in situ hybridization was performed using biotin-labeled HPV 63 DNA and digoxigenin-labeled HPV 1 DNA. The distribution of the genomes of these two viruses was examined in comparison with the histologic features in the lesion. The copy numbers of HPV 63 and HPV 1 were compared on agarose gel electrophoresis, stained with ethidium-bromide.

RESULTS

We demonstrated the presence of the DNA of both HPV 1 and HPV 63 within the same nucleus of a plantar wart. In spite of the double infection of these two viruses in a cell and more or less equal copy numbers of the viruses, the cytopathogenic effect of only HPV 63 was seen in the cells.

CONCLUSIONS

This is the first report of double infection of two different types of HPV within the same nucleus. Our findings suggest the possible interference that two HPV types could have on each other in inducing the HPV type specific cytopathogenic effects.

cDNA sequence diversity and genomic clusters of major surface glycoprotein genes of Pneumocystis carinii

The major surface glycoprotein (MSG) of Pneumocystis carinii plays a crucial role in the pathobiology of P. carinii, which often causes fatal pneumonia in AIDS patients. The cDNAs encoding MSG antigens were cloned from a lambda gt11 expression library of rat-derived P. carinii by immunoscreening. The cloned cDNAs constituted a gene family containing approximately 70% amino acid identity between subtypes. The diversity of MSG cDNAs was high and reflected the genomic structure of MSG genes clustered in the P. carinii chromosomes. These multiple genes may account for the high-level expression of MSG that could generate potential variations in the cell surface. Moreover, the MSG sequences have significant sequence homology to tropomyosins and myosins, suggesting physical or functional association with the membrane cytoskeleton.

Two novel types of human papillomavirus, HPV 63 and HPV 65: comparisons of their clinical and histological features and DNA sequences to other HPV types

An association exists between verrucae presenting with specific histological features and the type of HPV inducing the lesion. An HPV 1 induced lesion is associated with a granular type of intracytoplasmic inclusion body (Gr-ICB), whereas HPV 4 is associated with the homogeneous type of ICB (Hg-ICB). A third type of inclusion body, a filamentous type (F1-ICB), was found to be present in multiple punctate keratotic lesions. A novel type of papillomavirus, HPV 63, was present in such lesions. After cloning, characterization and sequencing of its DNA genome, HPV 63, although still very distinct (< 66% nucleotide homology), could be grouped with HPV 1. Upon histological examination of verrucous lesions presenting clinically with grey to black pigmentation, the Hg-ICB present were very characteristic. These lesions were infected with HPV 4, HPV 60, or HPV 65. The majority of the lesions contained the novel type HPV 65. This viral DNA was isolated and characterized. Its DNA sequence has an 83% homology to that of HPV 4, whereas both are more distantly related to HPV 60, an HPV isolated from an epidermoid cyst.

Different effects of substitutions at residues 224 and 228 of MHC class I on the recognition of CD8

Previous studies indicated that weak xenoresponse to HLA class I by mouse T cells is due to the inefficient interaction of mouse CD8 with the alpha 3 domain of HLA class I. The present study using chimeric H-2Kb molecules with recombinant alpha 3 domain between H-2Kb and HLA-B7 as well as single amino acid mutants of H-2Kb demonstrated that each substitution at residues 224 and 228 affects recognition of CD8-dependent mouse CTL clones. On the other hand, reactivity of IL-2-producing H-2Kb-specific T cell hybridoma transfected with mouse CD8 alpha was abrogated by substitution at residue 224 but not by that at residue 228. This indicates that the substitution at residue 228 affects recognition of CD8-dependent CTL but does not critically affect binding of CD8 to MHC class I molecules, although residue 224 abrogates binding of CD8. The model structure of the alpha 3 domain of H-2Kb suggests that the substitution at residue 224 induces conformational change of CD8 binding loop, whereas minimum structure change by the substitution at residue 228 is expected. It is therefore speculated that minimum structure change of CD8 binding loop by substitution at residue 228 may influence binding affinity of CD8, which abrogates recognition of CD8-dependent CTL but not IL-2 production of the CD8-dependent T cell hybridoma.

Different effects of substitutions at residues 224 and 228 of MHC class I on the recognition of CD8

Previous studies indicated that weak xenoresponse to HLA class I by mouse T cells is due to the inefficient interaction of mouse CD8 with the alpha 3 domain of HLA class I. The present study using chimeric H-2Kb molecules with recombinant alpha 3 domain between H-2Kb and HLA-B7 as well as single amino acid mutants of H-2Kb demonstrated that each substitution at residues 224 and 228 affects recognition of CD8-dependent mouse CTL clones. On the other hand, reactivity of IL-2-producing H-2Kb-specific T cell hybridoma transfected with mouse CD8 alpha was abrogated by substitution at residue 224 but not by that at residue 228. This indicates that the substitution at residue 228 affects recognition of CD8-dependent CTL but does not critically affect binding of CD8 to MHC class I molecules, although residue 224 abrogates binding of CD8. The model structure of the alpha 3 domain of H-2Kb suggests that the substitution at residue 224 induces conformational change of CD8 binding loop, whereas minimum structure change by the substitution at residue 228 is expected. It is therefore speculated that minimum structure change of CD8 binding loop by substitution at residue 228 may influence binding affinity of CD8, which abrogates recognition of CD8-dependent CTL but not IL-2 production of the CD8-dependent T cell hybridoma.

A mutation (Trp1193-->Leu1193) in the tyrosine kinase domain of the insulin receptor associated with type A syndrome of insulin resistance

We evaluated a 35-year-old diabetic male patient with type A insulin resistance, showing acanthosis nigricans. Insulin binding to the patient's Epstein-Barr-virus transformed lymphocytes was mildly reduced. The maximal insulin-stimulated autophosphorylation of the insulin receptor from the patient's transformed lymphocytes was decreased to 45% of that from the control subjects. On examination, the biological activities of insulin and insulin-like growth factor I in the patient's cultured fibroblasts, insulin sensitivity of amino isobutyric acid uptake and thymidine incorporation was decreased, but insulin-like growth factor I action was normal. The sequence analysis of amplified genomic DNA revealed that the patient was heterozygous for a mutation substituting Leu for Trp at codon 1193 in exon 20 of the insulin receptor gene. The patient's mother and sister were also heterozygous for a mutation in the insulin receptor gene that substituted Leu for Trp1193 in the beta subunit of the receptor. Therefore, the mutation causes insulin resistance in a dominant fashion. They were less hyperglycaemic and more hyperinsulinaemic than the proband after glucose loading. The mother had diabetes mellitus but did not show acanthosis nigricans, while the sister did not have diabetes and showed acanthosis nigricans. These results suggest that this mutation causes defective tyrosine kinase activity of the insulin receptor, which results in insulin resistance. Insulin action and phenotypic appearance may be mediated by different factors.