An image-guided precision proton radiation platform for preclinical in vivo research.

There are many unknowns in the radiobiology of proton beams and other particle beams. We describe the development and testing of an image-guided low-energy proton system optimized for radiobiological research applications. A 50 MeV proton beam from an existing cyclotron was modified to produce collimated beams (as small as 2 mm in diameter). Ionization chamber and radiochromic film measurements were performed and benchmarked with Monte Carlo simulations (TOPAS). The proton beam was aligned with a commercially-available CT image-guided x-ray irradiator device (SARRP, Xstrahl Inc.). To examine the alternative possibility of adapting a clinical proton therapy system, we performed Monte Carlo simulations of a range-shifted 100 MeV clinical beam. The proton beam exhibits a pristine Bragg Peak at a depth of 21 mm in water with a dose rate of 8.4 Gy min-1 (3 mm depth). The energy of the incident beam can be modulated to lower energies while preserving the Bragg peak. The LET was: 2.0 keV µm-1 (water surface), 16 keV µm-1 (Bragg peak), 27 keV µm-1 (10% peak dose). Alignment of the proton beam with the SARRP system isocenter was measured at 0.24 mm agreement. The width of the beam changes very little with depth. Monte Carlo-based calculations of dose using the CT image data set as input demonstrate in vivo use. Monte Carlo simulations of the modulated 100 MeV clinical proton beam show a significantly reduced Bragg peak. We demonstrate the feasibility of a proton beam integrated with a commercial x-ray image-guidance system for preclinical in vivo studies. To our knowledge this is the first description of an experimental image-guided proton beam for preclinical radiobiology research. It will enable in vivo investigations of radiobiological effects in proton beams.

Congenital cardiomyopathy and pulmonary hypertension: another fatal variant of cytochrome-c oxidase deficiency.

Biventricular hypertrophy was noted at 24 weeks' gestation in a fetus with isolated cytochrome-c oxidase (COX) deficiency. Shock, caused by hypertrophic cardiomyopathy and severe pulmonary hypertension, led to the patient's death on day 6. His phenotype defines a new lethal variant of COX deficiency characterized by prenatal-onset cardiopulmonary pathophysiology.

The expression of WT1 in the differentiation of rhabdomyosarcoma from other pediatric small round blue cell tumors.

The WT1 gene encodes a transcription factor implicated in normal and neoplastic development. The purpose of this study was to evaluate the diagnostic utility of a commercial WT1 antibody on a variety of pediatric small round blue cell tumors (SRBCT). A mouse monoclonal antibody (clone: 6F-H2, DAKO) raised against the N-terminal amino acids 1-181 of the human WT1 protein was tested. Microscopic sections from 66 specimens were stained using an antigen retrieval protocol with trypsin. The tumors included peripheral neuroectodermal tumors (PNET/Ewing's), neuroblastomas, desmoplastic small round cell tumors (DSRCT), lymphomas, Wilms' tumors, and rhabdomyosarcomas (RMS). One RMS case was investigated by Western blot analysis and RT-PCR to confirm the antibody specificity. A strong cytoplasmic staining was demonstrated in all RMS (11/11). The Western blot analysis confirmed the WT1 protein in the tissue, and the RT-PCR confirmed the presence of WT1 mRNA in the peripheral blood and tissue of one RMS patient. The Wilms' tumors had a variable nuclear and/or cytoplasmic positivity in most (17/24) cases. All PNET/Ewing's were negative. The nuclei of two lymphoblastic lymphomas stained strongly. A weak nuclear or cytoplasmic staining was reported in a few DSRCT (3/5), lymphomas (2/10), and neuroblastomas (2/8). This is a useful antibody in the differentiation of RMS from other SRBCTs. A strong cytoplasmic staining favors an RMS, and a strong nuclear staining is suggestive of a Wilms' tumor. A role for WT1 in the pathogenesis of rhabdomyosarcomas is raised. The limited sampling precludes any conclusions regarding the value of tissue or peripheral blood analysis for WT1 mRNA in patients with rhabdomyosarcoma.

Lack of germline transmission of vector sequences following systemic administration of recombinant AAV-2 vector in males.

A potential consequence of systemic administration of viral vectors is the inadvertent introduction of foreign DNA into recipient germ cells. To evaluate the safety of in vivo recombinant adeno-associated virus (rAAV) mediated gene transfer approaches for hemophilia B, we explored the risk of germline transmission of vector sequences following intramuscular (IM) injection of rAAV in four species of male animals (mouse, rat, rabbit and dog). In vector biodistribution studies in mice and rats, there is a dose-dependent increase in the likelihood that vector sequences can be detected in gonadal DNA using a sensitive PCR technique. However, in dogs DNA extracted from semen is negative for vector sequences. To address this discrepancy, studies were done in rabbits, and both semen and testicular DNAs were analyzed for the presence of vector sequences. These studies showed that no AAV vector sequences were detected in DNA extracted from rabbit semen samples collected at time points ranging from 7 to 90 days following IM injection of 1 x 10(13) vector genomes rAAV (vg) per kg. In contrast, DNA extracted from gonadal tissue was positive for vector sequences, but the positive signals diminished in number and strength with time. By FISH analysis, AAV signals were localized to the testis basement membrane and the interstitial space; no intracellular signal was observed. We observed similar findings following hepatic artery administration of rAAV in rats and dogs, suggesting that our findings are independent of the route of administration of vector. Attempts to transduce isolated murine spermatogonia directly with AAV-lacZ were unsuccessful. In clinical studies human subjects injected IM with an AAV vector at doses up to 2 x 10(12) vg/kg have shown no evidence of vector sequences in semen. Together, these studies suggest that rAAV introduced into skeletal muscle or the hepatic artery does not transduce male germ cells efficiently. We conclude that the risk of inadvertent germline transmission of vector sequences following IM or hepatic artery injection of AAV-2 vectors is extremely low.

Abnormal germ cell development in cryptorchidism.

BACKGROUND: Previous studies suggest that two fundamental, probably androgen-dependent, steps in maturation of germ cells normally occur in the prepubertal testis: the disappearance of gonocytes (the fetal stem cell pool) and the appearance of adult dark spermatogonia (the adult stem cell pool) at 2-3 months of age and the appearance of primary spermatocytes (the onset of meiosis) at 4-5 years. Previous studies of small series of cryptorchid boys suggest that both steps are defective in undescended testes and to a lesser degree in descended testes contralateral to unilaterally undescended testes. The purpose of this study is to confirm the previous findings of defective germ cell maturation in a large series of boys with unilateral undescended testes. PATIENTS: Seven hundred and sixty-seven boys with unilateral cryptorchidism who had orchidopexy and bilateral testicular biopsies between birth and 9 years of age were studied. MATERIALS AND METHODS: Total and differential germ cell counts were performed on semithin histologic sections of the biopsies. The results from the undescended and contralateral descended testes were compared using the Wilcoxon signed-rank test and the Wilcoxon-Whitney-Mann U test. RESULTS: Gonocytes failed to disappear and adult dark spermatogonia failed to appear in undescended testes under 1 year of age indicating a defect in the first step in maturation at 2-3 months resulting in failure to establish an adequate adult stem cell pool. Primary spermatocytes failed to appear in undescended testes and appeared in only 19% of contralateral descended testes at 4-5 years of age indicating a defect in the onset of meiosis. CONCLUSION: Unilaterally undescended testes fail to establish an adequate adult stem cell pool which normally occurs at 2-3 months of age and fail to establish adequate meiosis which normally occurs at 4-5 years of age. Similar but less severe changes are seen in the contralateral descended testes. Defects in the two pubertal steps in germ cell maturation are associated with reduced total germ cell counts.

Hormonal therapy for the subfertility of cryptorchidism.

BACKGROUND: The subfertility of cryptorchidism correlates with severely reduced total germ cell counts in prepubertal testicular biopsies of undescended testes. Reduced total germ cell counts are associated with defects in the two prepubertal steps in maturation and proliferation in germ cells: first, the transformation of the fetal stem cell pool (gonocytes) into the adult stem cell pool (adult dark spermatogonia) at two to three months of age and, second, the transformation of adult dark spermatogonia into primary spermatocytes (meiosis) at 4-5 years. The defects in maturation are associated with blunting of the normal surges in gonadotropins and testosterone. Prepubertal treatment with gonadotropin-releasing hormones would theoretically trigger normal germ cell maturation and proliferation and thereby improve total germ cell counts and improve fertility. Prepubertal treatment of cryptorchidism with the GnRH analogue Buserelin has resulted in improved total germ cell counts and improved spermiograms. The purpose of this report is to describe the results of treatment of cryptorchidism with the GnRH analogue Naferelin. PATIENTS: Twelve boys with cryptorchidism, 6 unilateral and 6 bilateral, and severely reduced germ cell counts in testicular biopsies were treated with Naferelin following successful orchidopexy and bilateral testicular biopsies. Response of the total germ cell counts was assessed in follow-up bilateral biopsies within 5 months of completing the hormonal therapy. RESULTS: Eight of the 12 boys (5 of the 6 with unilateral and 3 of the 6 with bilateral cryptorchidism) showed improvement in the total germ cell counts in one or both testes. All 8 had a poor prognosis for fertility pretreatment and a good prognosis for fertility posttreatment. Of the 5 with unilateral cryptorchidism who improved, 2 showed improvement in both testes; and 3, only in the contralateral descended testes. All 3 of the boys with bilateral cryptorchidism who improved showed improvement in both testes. Testes with absence of germ cells and older patients tended to show no improvement. Of the 6 contralateral descended, 5 (83%) improved, and of the 18 undescended testes, 8 (44%) improved. CONCLUSIONS: In this preliminary study, Naferelin therapy appears to induce improvement in the total germ cell counts and the prognosis for future fertility in 75% of patients.

The histopathology of iatrogenic cryptorchid testis: an insight into etiology.

PURPOSE: Iatrogenic undescended testis may develop after inguinal hernia repair, presumably as a result of mechanical tethering of the testis or cord in scar tissue. Because some true cryptorchid testes appear to be completely descended at birth and later ascend during childhood, some iatrogenic undescended testes may be low lying undescended testes. To determine whether iatrogenic undescended testes may be unrecognized cryptorchid testes at herniorrhaphy we examined biopsies of iatrogenic undescended testes and the corresponding contralateral descended testis. MATERIALS AND METHODS: Between 1985 and 1999 bilateral testis biopsies were obtained at orchiopexy in 37 boys 1.5 to 11.8 years old who previously underwent inguinal hernia correction. Histomorphometric analysis of germ cell counts was performed on the undescended and contralateral descended testes, and compared to the count in bilateral biopsies of 37 age and position matched patients with true unilateral cryptorchidism. RESULTS: There were no significant differences in volume or total and differential germ cell counts in the undescended and contralateral descended testes in the study groups and age matched controls with primary unilateral cryptorchidism. The mean number of germ cells per tubule in the undescended testis in patients with a greater than 5-year interval from herniorrhaphy to orchiopexy was significantly decreased compared to those with an operative interval of less than 5 years (0.27 +/- 0.33 versus 0.93 +/- 1.4, p = 0.026). CONCLUSIONS: Some patients with iatrogenic undescended testis may have an unrecognized low cryptorchid testis. Careful physical examination before and after inguinal surgery is recommended. The early repair of iatrogenic undescended testis is warranted to prevent further damage.

Placental cellular immune response in women infected with human parvovirus B19 during pregnancy.

Human parvovirus B19 can cause congenital infection with variable morbidity and mortality in the fetus and neonate. Although much information exists on the B19-specific antibody response in pregnant women, little information is available describing the cell-mediated immune (CMI) response at the maternal-fetal interface. The focus of this study was to characterize the CMI response within placentas from women who seroconverted to B19 during their pregnancies and compare it to controls. Immunohistochemical techniques were used to identify the various immune cells and the inflammatory cytokine present within placental tissue sections. Group 1 consisted of placentas from 25 women whose pregnancies were complicated by B19 infection; 6 women with good outcome (near-term or term delivery), and 19 with poor outcome (spontaneous abortion, nonimmune hydrops fetalis, or fetal death). Group 2 consisted of placentas from 20 women whose pregnancies were complicated with nonimmune hydrops fetalis of known, noninfectious etiology. Group 3 consisted of placentas from eight women whose pregnancies ended in either term delivery or elective abortion. The results of the study revealed a statistically significant increase in the number of CD3-positive T cells present within placentas from group 1 compared to group 2 or 3 (13.3 versus 2 and 1, respectively) (P < 0.001). In addition, the inflammatory cytokine interleukin 2 was detected in every placenta within group 1 but was absent from all placentas evaluated from groups 2 and 3. Together, these findings demonstrate evidence for an inflammation-mediated cellular immune response within placentas from women whose pregnancies are complicated with B19 infection.

Abnormal testicular histology in Michelin tire syndrome.

An 8-year-old male is described with Michelin tire syndrome and an abnormal testicular histology which has not previously been reported in this syndrome.

Pyricularia grisea Causing Gray Leaf Spot of Perennial Ryegrass Turf: Population Structure and Host Specificity.

Gray leaf spot is a serious disease of perennial ryegrass (Lolium perenne) turf in the United States. Isolates of Pyricularia grisea causing the disease in perennial ryegrass were characterized using molecular markers and pathogenicity assays on various gramineous hosts. Genetic relationships among perennial ryegrass isolates were determined using different types of trans-posons as probes. Phylogenetic analysis using Pot2 and MGR586 probes, analyzed with AMOVA (analysis of molecular variance), showed that these isolates from perennial ryegrass consist of three closely related lineages. All the isolates belonged to a single mating type, MAT1-2. Among 20 isolates from 16 host species other than perennial ryegrass, only the isolates from wheat (Triticum aestivum) and triticale (× Triticosecale), showed notable similarity to the perennial ryegrass isolates based on their Pot2 fingerprints. The copy number and fingerprints of Pot2 and MGR586 in isolates of P. grisea from perennial ryegrass indicate that they are genetically distinct from the isolates derived from rice (Oryza sativa) in the United States. The perennial ryegrass isolates also had the same sequence in the internal transcribed spacer (ITS) region of the genes encoding ribosomal RNA as that of the wheat and triticale isolates, and exhibited rice isolate sequence polymorphisms. In pathogenicity assays, all the isolates of P. grisea from Legacy II perennial ryegrass caused characteristic blast symptoms on Marilee soft white winter wheat, Bennett hard red winter wheat, Era soft white spring wheat, and Presto triticale, and they were highly virulent on these hosts. An isolate from wheat and one from triticale (from Brazil) were also highly virulent on perennial ryegrass and Rebel III tall fescue (Festuca arundinacea). None of the isolates from perennial ryegrass caused the disease on Lagrue rice, and vice versa. Understanding the population structure of P. grisea isolates infecting perennial ryegrass and their relatedness to isolates from other gramineous hosts may aid in identifying alternate hosts for this pathogen.

Ectopic and undescended testes: 2 variants of a single congenital anomaly?

PURPOSE: We compared pathological findings in ectopic and undescended testis to determine whether the pathological evidence supports the hypothesis that the 2 conditions are variants of the same congenital anomaly. MATERIALS AND METHODS: We identified 24 boys with ectopic testis not in the superficial inguinal pouch of Denis Browne. Seven boys were excluded from study due to unavailable clinical records for 3, contralateral undescended testis in 2 and inadequate biopsy specimens in 2. Pathological findings of ectopic testis in the remaining 17 patients were compared with those of age matched patients with unilateral undescended testis. Total germ cell count, testicular volume, patency of the processus vaginalis and epididymal abnormalities were compared. Data were analyzed using the Wilcoxon matched pairs signed rank and Fisher's exact tests. RESULTS: No difference was noted in total germ cell count (p = 0.33), testicular volume (p = 0.1475), processus vaginalis patency (p = 0.0854) or epididymal abnormalities (p = 1.00) in the 2 groups. Of the 24 boys (8%) with ectopic testis 2 also had a contralateral undescended testis. CONCLUSIONS: Similar pathological findings in ectopic and undescended testes as well as the association of ectopic testis with a contralateral undescended testis suggest that ectopic and undescended testes are variants of the same congenital anomaly. Thus, boys with ectopic testis may have an increased incidence of subfertility and testicular malignancy. This spectrum of abnormal testicular position, and its range of pathological conditions and complications may appropriately be called the undescended testis sequence.

Testicular volume does not predict germ cell count in patients with cryptorchidism.

PURPOSE: A germ cell count of less than 0.2 germ cell per tubule on the prepubertal biopsy of cryptorchid testes predicts abnormal spermiograms and decreased fertility in adulthood, and may be used to select patients for post-orchiopexy hormonal therapy. Testicular volume directly correlates with testicular function and spermiogenesis. We determined whether testicular volume would predict the total germ cell count accurately enough to replace testicular biopsy in the modern management of cryptorchidism. MATERIALS AND METHODS: At our hospital 723 patients younger than 9 years with cryptorchidism (unilateral in 619 and bilateral in 104) underwent orchiopexy and bilateral testicular biopsies. These patients had not undergone groin surgery or hormonal therapy previously and had at least 50 tubules in each testicular biopsy. Testicular volume and position, patient age and germ cell counts were analyzed. The generalized estimating equation was used to determine whether a correlation existed between testicular volume and germ cell count. RESULTS: The generalized estimating equation demonstrated a direct correlation between testicular volume and germ cell count. However, germ cell counts predicted from testicular volume varied widely within the 95% confidence intervals. Testes with less than 0.2 germ cell per tubule cannot be reliably distinguished from those with greater than 0.2 germ cell per tubule. CONCLUSIONS: Testicular volume does not accurately predict the germ cell count in patients with undescended testes, cannot be used to select patients for post-orchiopexy hormonal therapy and cannot replace testicular biopsy in the modern management of cryptorchidism.

The role of renal salvage procedures for bilateral Wilms tumor: a 15-year review.

PURPOSE: We reviewed our experience with renal salvage procedures in patients with bilateral Wilms tumor to determine the clinical outcome. MATERIALS AND METHODS: From 1982 to 1997, 23 children with bilateral Wilms tumor were treated with partial nephrectomy at our institution, including 7 who were also treated with brachytherapy. Medical history, use and response to chemotherapy and brachytherapy, operative records, renal function, pathological results, survival, and techniques for partial and repeat nephrectomy and brachytherapy were reviewed. RESULTS: We treated 8 boys and 15 girls, of whom 21 who presented with synchronous bilateral Wilms tumor underwent primary chemotherapy followed by secondary partial nephrectomy. A total of 44 partial nephrectomies were performed and brachytherapy was done in 7 patients. Ten children have normal renal function and no disease, 10 are dead and 2 have metastatic disease. Anaplasia was the most significant factor associated with an unfavorable outcome (p = 0.003). Of the patients who were cured 60% had a positive response to initial chemotherapy compared with only 25% who had an unfavorable outcome (p = 0.09). No significant differences were noted with respect to gender, age at presentation, highest local tumor stage at presentation or initial nephrectomy. No patient treated with brachytherapy had local recurrence. CONCLUSIONS: Preoperative chemotherapy followed by nephron sparing surgery is indicated in patients with bilateral Wilms tumor, while in those with diffuse anaplasia nephron sparing surgery is contraindicated. Brachytherapy should be considered for treating local disease involving chemoresistant tumors.

Limb deformations in oligohydramnios sequence: effects of gestational age and duration of oligohydramnios.

In order to study the pathogenesis of prenatal deformities, we reviewed maternal histories, delivery records, pathology reports, radiographs, and photographs of 90 fetuses with prenatally documented oligohydramnios at gestational ages from 14 weeks to term. The causes of oligohydramnios included premature rupture of membranes (44 cases), fetal renal insufficiency (25 cases), idiopathic (15 cases), and twin-twin transfusion (6 cases). The fetuses were grouped according to gestational age at delivery and duration of oligohydramnios. Sixty-three fetuses (70%) had documented contractures. As expected, contractures were more frequent with earlier onset and longer duration of oligohydramnios. During the 2nd trimester, the frequency of contractures in fetuses with oligohydramnios was 77% compared to 52% in the 3rd trimester (chi(2) = 5.33, 1 df, P =.02). Considering all gestational ages together, 57% of fetuses had contractures after less than 2 weeks of oligohydramnios compared to 81% of fetuses with a longer duration of oligohydramnios (chi2 = 6.23, 1 df, P <.02). The type of contracture varied with gestational age. Clubfoot was the most frequent at all ages, but hand contractures such as camptodactyly were common only in the 2nd trimester while the broad flat hand originally described in Potter sequence was found almost exclusively in the fetuses with oligohydramnios in the 3rd trimester. Of the 63 fetuses with oligohydramnios and contractures, 25 (40%) had either additional malformations or family history that could explain contractures independent of oligohydramnios.

Comparison of plasma total homocysteine measurements in 14 laboratories: an international study.

BACKGROUND: Information on interlaboratory variation and especially on methodological differences for plasma total homocysteine is lacking. METHODS: We studied 14 laboratories that used eight different method types: HPLC with electrochemical detection (HPLC-ED); HPLC with fluorescence detection (HPLC-FD) further subdivided by type of reducing/derivatizing agent; gas chromatography/mass spectrometry (GC/MS); enzyme immunoassay (EIA); and fluorescence polarization immunoassay (FPIA). Three of these laboratories used two methods. The laboratories participated in a 2-day analysis of 46 plasma samples, 4 additional plasma samples with added homocystine, and 3 plasma quality-control (QC) pools. Results were analyzed for imprecision, recovery, and methodological differences. RESULTS: The mean among-laboratory and among-run within-laboratory imprecision (CV) was 9.3% and 5.6% for plasma samples, 8.8% and 4.9% for samples with added homocystine, and 7.6% and 4.2% for the QC pools, respectively. Difference plots showed values systematically higher than GC/MS for HPLC-ED, HPLC-FD using sodium borohydride/monobromobimane (however, for only one laboratory), and EIA, and lower values for HPLC-FD using trialkylphosphine/4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole. The two HPLC-FD methods using tris(2-carboxyethyl) phosphine/ammonium 7-fluoro-2,1,3-benzoxadiazole-4-sulfonate (SBD-F) or tributyl phosphine/SBD-F, and the FPIA method showed no detectable systematic difference from GC/MS. CONCLUSIONS: Among-laboratory variations within one method can exceed among-method variations. Some of the methods tested could be used interchangeably, but there is an urgent need to improve analytical imprecision and to decrease differences among methods.

An unusual subset of cryptorchidism: possible end organ failure.

PURPOSE: A paucity of germ cells exists in the cryptorchid gonad that usually correlates with a similar finding in the contralateral descended testis. However, we have noted a small number of boys with cryptorchidism in whom there is a significant difference between the histological evaluation of the cryptorchid testis and the normal descended testis that may indicate a different etiology. MATERIALS AND METHODS: From 1986 to 1991, 1,426 boys with unilateral cryptorchidism underwent orchiopexy, of whom 752 also underwent bilateral testicular biopsy. Testicular volume and position, and patency of the processus vaginalis were examined. Biopsies were fixed in 2% glutaraldehyde and embedded in Epon. Semithin tissue sections were analyzed by 2 independent investigators. The number of total germ cells, gonocytes, adult dark and pale spermatogonia, primary spermatocytes and Leydig cells was assessed. RESULTS: Of the 1,426 boys the undescended testis was on the right side in 726 and on the left side in 658 (52 versus 48%, p = 0068). Of the 752 boys who underwent bilateral biopsy 42 (5.6%) 1.1 to 16 years old (mean age plus or minus standard deviation 0 5.2 +/- 3.65) had a poor fertility index of less than 0.2 germ cell per tubule in the cryptorchid gonad, although the germ cell count in the descended testis was normal. Of the 42 testes in this special group of boys 30 (71%) were on the right side (Fisher's exact test p <0.23), including 16 (38%) in an intra-abdominal or high canalicular position. The processus vaginalis was patent in 86% of the intra-abdominal testes and in 100% of those located at the tubercle but in only 25% of those in a pre-scrotal position. While average germ cell count in the cryptorchid testis was 0.06 per tubule with abnormal germ cell maturation, number was normal (greater than 2 germ cells per tubule) in the contralateral descended testis with a normal distribution of adult dark and pale spermatogonia, and primary spermatocytes. Average volume of the cryptorchid testis was significantly less than that of the descended testis (1.20 +/- 0.35 versus 1.60 +/- 0.68 mm.3, p <0.0001). CONCLUSIONS: Based on the normal scrotal testis the fertility prognosis is good in this small subgroup of boys with cryptorchidism. Rather than the usual endocrinopathy of cryptorchidism, the undescended testis in these boys may be the result of end organ failure. These patients with favorable fertility potential may be recognized only if each testis is biopsied at unilateral orchiopexy.

PCR-based genotyping of epidemic and preepidemic Trichoderma isolates associated with green mold of Agaricus bisporus.

We used randomly amplified polymorphic DNA (RAPD)-PCR to estimate genetic variation among isolates of Trichoderma associated with green mold on the cultivated mushroom Agaricus bisporus. Of 83 isolates examined, 66 were sampled during the recent green mold epidemic, while the remaining 17 isolates were collected just prior to the epidemic and date back to the 1950s. Trichoderma harzianum biotype 4 was identified by RAPD analysis as the cause of almost 90% of the epidemic-related episodes of green mold occurring in the major commercial mushroom-growing region in North America. Biotype 4 was more closely allied to T. harzianum biotype 2, the predominant pathogenic genotype in Europe, than to the less pathogenic biotype 1 and Trichoderma atroviride (formerly T. harzianum biotype 3). No variation in the RAPD patterns was observed among the isolates within biotype 2 or 4, suggesting that the two pathogenic biotypes were populations containing single clones. Considerable genetic variation, however, was noted among isolates of biotype 1 and T. atroviride from Europe. Biotype 4 was not represented by the preepidemic isolates of Trichoderma as determined by RAPD markers and PCR amplification of an arbitrary DNA sequence unique to the genomes of biotypes 2 and 4. Our findings suggest that the onset of the green mold epidemic in North America resulted from the recent introduction of a highly virulent genotype of the pathogen into cultivated mushrooms.