Genetic newborn screening and digital technologies: A project protocol based on a dual approach to shorten the rare diseases diagnostic path in Europe

Since 72% of rare diseases are genetic in origin and mostly paediatrics, genetic newborn screening represents a diagnostic "window of opportunity". Therefore, many gNBS initiatives started in different European countries. Screen4Care is a research project, which resulted of a joint effort between the European Union Commission and the European Federation of Pharmaceutical Industries and Associations. It focuses on genetic newborn screening and artificial intelligence-based tools which will be applied to a large European population of about 25.000 infants. The neonatal screening strategy will be based on targeted sequencing, while whole genome sequencing will be offered to all enrolled infants who may show early symptoms but have resulted negative at the targeted sequencing-based newborn screening. We will leverage artificial intelligence-based algorithms to identify patients using Electronic Health Records (EHR) and to build a repository "symptom checkers" for patients and healthcare providers. S4C will design an equitable, ethical, and sustainable framework for genetic newborn screening and new digital tools, corroborated by a large workout where legal, ethical, and social complexities will be addressed with the intent of making the framework highly and flexibly translatable into the diverse European health systems.

Community data-driven approach to identify pathogenic founder variants for pan-ethnic carrier screening panels

BACKGROUND

The American College of Medical Genetics and Genomics (ACMG) recently published new tier-based carrier screening recommendations. While many pan-ethnic genetic disorders are well established, some genes carry pathogenic founder variants (PFVs) that are unique to specific ethnic groups. We aimed to demonstrate a community data-driven approach to creating a pan-ethnic carrier screening panel that meets the ACMG recommendations.

METHODS

Exome sequencing data from 3061 Israeli individuals were analyzed. Machine learning determined ancestries. Frequencies of candidate pathogenic/likely pathogenic (P/LP) variants based on ClinVar and Franklin were calculated for each subpopulation based on the Franklin community platform and compared with existing screening panels. Candidate PFVs were manually curated through community members and the literature.

RESULTS

The samples were automatically assigned to 13 ancestries. The largest number of samples was classified as Ashkenazi Jewish (n = 1011), followed by Muslim Arabs (n = 613). We detected one tier-2 and seven tier-3 variants that were not included in existing carrier screening panels for Ashkenazi Jewish or Muslim Arab ancestries. Five of these P/LP variants were supported by evidence from the Franklin community. Twenty additional variants were detected that are potentially pathogenic tier-2 or tier-3.

CONCLUSIONS

The community data-driven and sharing approaches facilitate generating inclusive and equitable ethnically based carrier screening panels. This approach identified new PFVs missing from currently available panels and highlighted variants that may require reclassification.

Performance comparison: exome sequencing as a single test replacing Sanger sequencing

Next generation sequencing tests are used routinely as first-choice tests in the clinic. However, systematic performance comparing the results of exome sequencing as a single test replacing Sanger sequencing of targeted gene(s) is still lacking. Performance comparison data are critically important for clinical case management. In this study, we compared Sanger-sequencing results of 258 genes to those obtained from next generation sequencing (NGS) using two exome-sequencing enrichment kits: Agilent-SureSelectQXT and Illumina-Nextera. Sequencing was performed on leukocytes and buccal-derived DNA from a single individual, and all 258 genes were sequenced a total of 11 times (using different sequencing methods and DNA sources). Sanger sequencing was completed for all exons, including flanking ± 8 bp regions. For the 258 genes, NGS mean coverage was > 20 × for > 98 and > 91% of the regions targeted by SureSelect and Nextera, respectively. Overall, 449 variants were identified in at least one experiment, and 407/449 (90.6%) were detected by all. Of the 42 discordant variants, 23 were determined as true calls, summing-up to a truth set of 430 variants. Sensitivity of true-variant detection was 99% for Sanger sequencing and 97-100% for the NGS experiments. Mean false-positive rates were 3.7E-6 for Sanger sequencing, 2.5E-6 for SureSelect-NGS and 5.2E-6 for Nextera-NGS. Our findings suggest a high overall concordance between Sanger sequencing and NGS performances. Both methods demonstrated false-positive and false-negative calls. High clinical suspicion for a specific diagnosis should, therefore, override negative results of either Sanger sequencing or NGS.

OneTwoTree: An online tool for phylogeny reconstruction

Phylogeny reconstruction is a key instrument in numerous biological analyses, ranging from evolutionary and ecology research, to conservation and systems biology. The increasing accumulation of genomic data makes it possible to reconstruct phylogenies with both high accuracy and at increasingly finer resolution. Yet, taking advantage of the enormous amount of sequence data available requires the use of computational tools for efficient data retrieval and processing, or else the process could quickly become an error-prone endeavour. Here, we present OneTwoTree (http://onetwotree.tau.ac.il/), a Web-based tool for tree reconstruction based on the supermatrix paradigm. Given a list of taxa names of interest as the sole input requirement, OneTwoTree retrieves all available sequence data from NCBI GenBank, clusters these into orthology groups, identifies the most informative set of markers, searches for an appropriate outgroup, and assembles a partitioned sequence matrix that is then used for the final phylogeny reconstruction step. OneTwoTree further allows users to control various steps of the process, such as the merging of sequences from similar clusters, or phylogeny reconstruction based on markers from a specific genome type. By comparing the performance of OneTwoTree to a manually reconstructed phylogeny of the Antirrhineae tribe, we show that the use of OneTwoTree resulted in substantially higher data coverage in terms of both taxon sampling and the number of informative markers assembled. OneTwoTree provides a flexible online tool for species-tree reconstruction, aimed to assist researchers ranging in their level of prior expertise in the task of phylogeny reconstruction.

Dioecy does not consistently accelerate or slow lineage diversification across multiple genera of angiosperms

Dioecy, the sexual system in which male and female organs are found in separate individuals, allows greater specialization for sex-specific functions and can be advantageous under various ecological and environmental conditions. However, dioecy is rare among flowering plants. Previous studies identified contradictory trends regarding the relative diversification rates of dioecious lineages vs their nondioecious counterparts, depending on the methods and data used. We gathered detailed species-level data for dozens of genera that contain both dioecious and nondioecious species. We then applied a probabilistic approach that accounts for differential speciation, extinction, and transition rates between states to examine whether there is an association between dioecy and lineage diversification. We found a bimodal distribution, whereby dioecious lineages exhibited higher diversification in certain genera but lower diversification in others. Additional analyses did not uncover an ecological or life history trait that could explain a context-dependent effect of dioecy on diversification. Furthermore, in-depth simulations of neutral characters demonstrated that such bimodality is also found when simulating neutral characters across the observed trees. Our analyses suggest that - at least for these genera with the currently available data - dioecy neither consistently places a strong brake on diversification nor is a strong driver.

Group A streptococcal osteomyelitis: severe presentation and course

AIM

To evaluate the course of group A streptococcal osteomyelitis associated with severe disease nowadays.

METHODS

Three consecutive cases of severe group A streptococcal disease with osteomyelitis in children that were documented in Beer Sheva, Israel are described in detail.

RESULTS

Two of the three cases were postvaricella. Early in the course of the disease, the presentation resembled that of severe cellulitis. All three patients had severe osteomyelitis and required surgery, and one patient developed chronic osteomyelitis. Sepsis was diagnosed in two cases.

CONCLUSION

Our cases are distinguishable from typical haematogenous staphylococcal osteomyelitis by the severe course and the extensive involvement of bone and soft tissues. The increase in severity of invasive group A streptococcal infections documented throughout the world could account for the difference between our complex cases and the previous reports.

Development of psoriatic lesions during acute and convalescent phases of Kawasaki disease

A 7-month-old infant developed a discrete pustular rash confined to both soles during the acute phase of Kawasaki disease. Histological examination of a pustular lesion from the sole of a foot showed subcorneal neutrophilic microabscesses, psoriasiform acanthosis with a thin granular layer and mononuclear perivascular infiltrates in the upper dermis, consistent with psoriasis. Following the standard treatment with intravenous gamma globulin, the initial symptoms and signs of Kawasaki disease resolved completely. Eight weeks later, psoriasiform plaques appeared on both cheeks and on the extensor surfaces of the forearms and legs. Skin biopsy from one of these lesions revealed psoriasiform epidermal hyperplasia, focal parakeratosis and dilated papillary capillaries. The patient was treated with mild-potency topical steroids that resulted in rapid and complete resolution of the skin lesions. Concurrent association of psoriatic skin lesions and Kawasaki disease might not be incidental and could stem from a common pathogenetic mechanism induced by superantigens.

Congenital insensitivity to pain with anhidrosis (CIPA): the spectrum of radiological findings

BACKGROUND

Congenital insensitivity to pain with anhidrosis (CIPA) is an exceedingly rare, hereditary, sensory autonomic neuropathy (HSAN).

AIM

To evaluate the various skeletal manifestations and cranial CT features in children affected by CIPA.

MATERIALS AND METHODS

In the semidesert area of the Negev, the Bedouin tribes constitute a closed society where consanguineous marriages are the custom. This has resulted in a group of 20 children being affected by this rare autosomal recessive HSAN. The skeletal surveys and CT scans of these 20 Bedouin patients, 12 girls and 8 boys, ages ranging between 1 month and 8 years, were retrospectively analysed. Cranial CT scans were performed in ten children because of neonatal hypotonia and psychomotor retardation. The skeletal findings were classified as follows: fractures, joint deformities, joint dislocations, osteomyelitis, avascular necrosis and acro-osteolysis.

RESULTS

All 20 patients had fractures of the extremities and acro-osteolysis of the fingers. Six had joint deformities. Three children had recurrent hip joint dislocations and another three had avascular necrosis. Ten patients presented with osteomyelitis of the limbs, acetabulum and scapula. The cranial CT scans disclosed mild brain volume loss with some ventriculomegaly.

CONCLUSIONS

CIPA is a severe autosomal recessive condition that leads to self-mutilation early in life and to fractures, osteomyelitis and limb amputation in older children. Mental retardation is common. Death from hyperpyrexia occurs in almost 20 % of patients in the first 3 years of life.

Outpatient management of acute mastoiditis with periosteitis in children

Children with acute mastoiditis with periosteitis are conventionally hospitalized for parenteral antibiotics and/or surgical treatment. However, if possible, effective and safe outpatient treatment is desirable. During a 36-month period, outpatient parenteral antibiotic therapy (once daily i.m. ceftriaxone) was evaluated in 32 children with acute mastoiditis, with clinical evidence of periosteitis. Inclusion criteria included otomicroscopic evidence of acute otitis media (AOM), displacement of the pinna, retroauricular swelling, erythema and tenderness. The treatment consisted of wide myringotomy and administration of i.m. antibiotics. Daily visits, by a combined team of an otolaryngologist and pediatric infectious disease specialist, were considered essential. Fourteen children (43%) were treated initially in the hospital (and subsequently as outpatients) and 18 (57%) children were treated entirely as outpatients. Mean duration of outpatient treatment was 7 days (range: 4-10). The overall clinical cure rate was 96.8%. One child underwent simple mastoidectomy. No serious side effects were observed. Our data suggests that many children with acute mastoiditis with periosteitis can be managed successfully and safely as outpatients by a combined team of otolaryngologists and infectious disease specialists.

Fine-needle bone biopsy to diagnose osteomyelitis

In 30 patients in whom osteomyelitis was suspected fine-needle bone biopsies (FNBB) were taken at the same time as bone was aspirated for bacteriological examination. The diagnosis of osteomyelitis was eventually confirmed in 15 patients; the other 15 had myositis (3), arthritis (3), trauma (2), microgeodic phalangeal syndrome (2), haematoma in a non-ossifying fibroma (1), and Ewing's sarcoma (1). In three patients no pathology was found. The temperature, WBC and ESR at presentation did not help to distinguish osteomyelitis from other conditions. FNBB, however, proved to be a useful additional investigation with a sensitivity for osteomyelitis of 87% and a specificity of 93%.

Fine-needle bone biopsy to diagnose osteomyelitis

In 30 patients in whom osteomyelitis was suspected fine-needle bone biopsies (FNBB) were taken at the same time as bone was aspirated for bacteriological examination. The diagnosis of osteomyelitis was eventually confirmed in 15 patients; the other 15 had myositis (3), arthritis (3), trauma (2), microgeodic phalangeal syndrome (2), haematoma in a non-ossifying fibroma (1), and Ewing's sarcoma (1). In three patients no pathology was found. The temperature, WBC and ESR at presentation did not help to distinguish osteomyelitis from other conditions. FNBB, however, proved to be a useful additional investigation with a sensitivity for osteomyelitis of 87% and a specificity of 93%.

Parenteral-oral switch in the management of paediatric pneumonia

In phase I of a 2-phase study, 56 evaluable children (0.8 to 5 years) with lobar or segmental pneumonia received intravenous or intramuscular ceftriaxone 50 mg/kg/day for 2 days followed by oral cefetamet pivoxil 20 mg/kg/day in 2 divided doses to complete 7 days of treatment. All patients achieved a clinical cure. In phase II, a randomised open multicentre study, 62 children with pneumonia received an identical regimen to phase I (arm A), and 59 children received ceftriaxone 50 mg/kg/day for 1 day followed by 6 days' treatment with cefetamet pivoxil 20 mg/kg/day (arm B). Patients from phase I and arm A were combined giving a total of 118 evaluable patients in arm A. At the end of treatment, 100% of patients in arm A and 96% in arm B achieved a clinical cure; cure was maintained in 99 and 98% of patients, respectively. Two (4%) patients in arm B failed therapy; in both cases, factors other than treatment failure may have accounted for the poor response. 11 and 12% of patients in treatment arms A and B, respectively, experienced adverse events; gastrointestinal events (nausea and/or vomiting) were reported in 9 and 8% of patients, respectively. In conclusion, 1 or 2 days' treatment with parenteral ceftriaxone before switching to oral cefetamet pivoxil was safe and effective in the treatment of childhood pneumonia. Therefore, parenteral-oral switch is a feasible treatment option in the treatment of serious paediatric community-acquired pneumonia.

Clinical features and epidemiology of invasive Kingella kingae infections in southern Israel

OBJECTIVE

To characterize the clinical spectrum and epidemiology of invasive Kingella kingae infections in children living in southern Israel.

DESIGN

Five-year observational, descriptive study.

POPULATION

Children in whom K. kingae was isolated from blood or other normally sterile body fluid.

RESULTS

Twenty-five patients with invasive K. kingae infection (13 male and 12 female) were identified. Twenty-four of these children were younger than 2 years. The annual incidence was 14.3, 27.4, and 31.9 cases per 100,000 children < or = 4 years, < or = 24 months, and < or = 12 months, respectively. Seventeen (68%) of 25 patients sought treatment between July and December. Concomitant upper respiratory tract infection or stomatitis was observed in 14 (56%) of the patients, suggesting a respiratory or buccal source for the infection. Four children were bacteremic: 2 of them suffered from a lower respiratory tract infection, and the remaining 2 had bacteremia with no evident focal infection. Twenty-one children had skeletal infections and none of them was bacteremic; 16 had septic arthritis, 3 had osteomyelitis, 1 had both osteomyelitis and septic arthritis of the adjacent joint, and 1 had dactylitis of the hand. Involvement of the ankle was unusually frequent among children with septic arthritis, whereas the calcaneus was involved in 3 of the 4 children with osteomyelitis. Antibiotic treatment resulted in full recovery in all cases, and only 2 patients with septic arthritis required surgical drainage.

CONCLUSION

Kingella kingae is a much more common cause of invasive infection in young children than has been previously recognized. The disease has a clear seasonal pattern, usually affects the skeletal system, frequently involves unusual bones and joints, and follows a benign course.

Ultrasound in diagnosis and management of acute haematogenous osteomyelitis in children

We reviewed the ultrasound findings in 59 children suspected of having bone infection. Twenty-nine were eventually proved to have acute haematogenous osteomyelitis and 26 of these showed characteristic ultrasound findings. Such changes were rare in 30 patients with other clinically similar conditions. Ultrasound examination was also able to detect the presence of subperiosteal pus and thus indicate the need for surgical treatment.

Otolaryngology and infectious disease team approach for outpatient management of serious pediatric infections requiring parenteral antibiotic therapy

Children with community-acquired serious otolaryngologic infections are conventionally hospitalized for parenteral antibiotic therapy. However, effective and safe outpatient therapy is desirable since it is less traumatic and less costly. During a 24-month period outpatient parenteral antibiotic therapy, usually once daily i.m. ceftriaxone, was evaluated in 41 children with serious otolaryngologic infections (acute mastoiditis, complicated otitis media, severe external otitis and severe sinusitis with orbital or periorbital involvement). Daily visits and compliant capable parents were considered essential for outpatient management. Diagnosis, plan for management and daily follow-up evaluations were carried out in cooperation by otolaryngology and infectious disease specialists. Nineteen children (45%) were treated initially in the hospital and 22 children (55%) were treated entirely as outpatients. The mean duration of outpatient treatment, using once daily i.m. ceftriaxone was 5.7 days (range 1-13). The overall clinical cure rate was 98% and no serious side effects were observed. One case of sinusitis-orbital cellulitis relapsed during therapy. Most patients and parents returned to normal life activities within 72 h from starting outpatient therapy. Our data suggest that many children with serious otolaryngologic infections can be managed successfully and safely as outpatients by a combined team of otolaryngology and infectious disease specialists.

Outpatient management of chronic suppurative otitis media without cholesteatoma in children

Prolonged antipseudomonal parenteral antibiotic therapy combined with daily aural toilet has been effective in resolving long standing ear discharge in children with chronic suppurative otitis media. However, such treatment suffered from the disadvantages of prolonged hospitalization. We conducted a prospective study to investigate the feasibility and efficacy of exclusive outpatient treatment of children with chronic suppurative otitis media without cholesteatoma who had failed ototopical/oral antimicrobial therapy. The treatment consisted of daily aural toilet (suction and debridement) and twice daily parenteral ceftazidime (50 mg/kg/dose). Thirty-seven children were included. The duration of discharge from the ear before treatment was 6 to 121 months (median, 30 months). Aerobic cultures yielded Pseudomonas aeruginosa in 97%, often with other organisms. The management and follow-up were performed jointly by otolaryngology and infectious diseases physicians using the hospital ambulatory services. The route of ceftazidime administration (intravenous or intramuscular) was chosen according to the parents' and patients' convenience. Discharge stopped within 3 to 20 days (median, 8 days) in all children but one. Seventy-six percent of the 29 children available for follow-up 12 months after treatment were still free of discharge. Our results demonstrate that a regiment combining daily aural toilet and twice daily parenteral ceftazidime is highly efficacious in resolving ear discharge in children with chronic suppurative otitis media without cholesteatoma and that such a regimen does not require hospitalization.

High prevalence of Kingella kingae in joint fluid from children with septic arthritis revealed by the BACTEC blood culture system

In an effort to improve detection of fastidious organisms, joint fluid aspirates of pediatric patients were inoculated into BACTEC 460 aerobic blood culture bottles, in addition to cultures on solid media. Culture records for the 1988 to 1991 period were reviewed to compare the performance of both methods for the recovery of pathogens. Overall, 216 children underwent a diagnostic joint tap, and 63 specimens grew significant organisms, including Kingella kingae in 14. While both methods were comparable for recovery of usual pathogens, with a single exception, K. kingae isolates were detected by the BACTEC system only. K. kingae appears to be a more common cause of septic arthritis in children than has been previously recognized. The BACTEC blood culture system enhances the recovery of K. kingae from joint fluid and improves bacteriologic diagnosis of pediatric septic arthritis.

Brucellosis induced avascular necrosis of the femoral head in a 7 year old child

The case is reported of a 7 year old Bedouin girl who presented with a three week history of fever and limp. Initial tests for rheumatoid factor, antinuclear antibodies, and brucella were negative. Two weeks after admission Brucella melitensis was cultured from bone marrow and synovial fluid samples. The patient improved after treatment with doxycillin and streptomycin, but radiographs of the right hip showed avascular necrosis of the right femoral head. A mild limp and limitation of motion in the right hip persisted 18 months after admission.

Once daily cefixime compared with twice daily trimethoprim/sulfamethoxazole for treatment of urinary tract infection in infants and children

We conducted a randomized prospective multicenter study to compare the safety and efficacy of once daily oral cefixime (8 mg/kg) to twice daily oral trimethoprim/sulfamethoxazole (TMP/SMX) (8/40 mg/kg/day) for the treatment of acute urinary tract infection in children ages 6 months to 13 years. Seventy-six patients (38 in each group) were studied. Thirty-seven percent were younger than 3 years of age. Escherichia coli was the most common isolate in both groups (85%). Eighty-five percent of all Gram-negative organisms were susceptible to TMP/SMX and all were susceptible to cefixime. Seventy-two percent of all patients were febrile at the time of diagnosis. Both groups were treated for 7 to 10 days. Peripheral white blood cell counts, erythrocyte sedimentation rate, body temperature and urinalysis returned to normal at the same rate in both groups. No failures were observed and relapse occurred in 3 cases within the 4 weeks after treatment (2 in the cefixime group and one in the TMP/SMX group). Side effects were observed in 14% of the cefixime group and 16% of the TMP/SMX group and were all mild enough not to necessitate discontinuation of therapy. We conclude that the efficacy and safety of cefixime administered once daily compared favorably with TMP/SMX administered twice daily for acute uncomplicated urinary tract infection.

Failure of ceftriaxone in the treatment of acute brucellosis

In an open, multicenter study conducted in Israel in 1989, 18 patients with acute brucellosis were randomized to receive either less than or equal to 2 g of intramuscularly administered ceftriaxone daily for at least 2 weeks or doxycycline for 4 weeks plus streptomycin for 2 weeks. All 10 patients treated with the combination of doxycycline plus streptomycin responded promptly, and their infections did not relapse during 6 months of follow-up. Of eight patients treated with ceftriaxone, six did not respond initially; when ceftriaxone was replaced by the combination of doxycycline and streptomycin, patients responded immediately. No relapses of infection were observed in these patients during follow-up. One patient who received ceftriaxone responded and remained well at the end of 6 months of follow-up, and one patient who initially responded to therapy with this drug experienced relapse of infection within 3 weeks but recovered when the doxycycline/streptomycin regimen was initiated. We conclude that despite encouraging data from in vitro studies and promising clinical studies, 2 g of ceftriaxone administered im daily should not be considered appropriate therapy for brucellosis.

Infections due to gram-positive organisms in children: possible role for teicoplanin

The disruptive effect on, and potentially hazardous exposure to nosocomial infection, together with the relative cost of hospitalization, of children favours the need for ambulatory care. An increasing proportion of infections in children are due to beta-lactam resistant Gram-positive organisms. Teicoplanin is proposed as a suitable candidate for treating paediatric patients with serious Gram-positive infections in hospital or ambulatory care. The experience acquired in children is still limited. However, over 200 paediatric patients have been treated with once or twice daily im or iv teicoplanin in daily doses of 3-10 mg/kg. The main clinical diagnoses were skin and soft tissue infections, skeletal infections and septicaemia. The drug was safe and clinical efficacy was greater than 90%. Comparative studies with defined uniform protocols are now required to assess the potential of this drug.

A program of outpatient parenteral antibiotic therapy for serious pediatric bacterial infections

A program set up in the Soroka University Medical Center, Beer Sheva, Israel, offers outpatient parenteral antibiotic therapy (OPAT) for children with serious bacterial infections. The following criteria must be met before a child is placed in this program: OPAT must be a suitable form of treatment for the infection, an appropriate drug must be available, the parents must be cooperative and well-informed, and 24-hour-a-day telephone communication and transportation between the home and hospital must be available. With use of ceftriaxone administered im, the OPAT program has shown positive results: a cure rate of 98.5% and an estimated savings of 1,334 hospital days for 140 patients over a 17-month period.

Parenteral fluoroquinolones in children with life-threatening infections

The new fluoroquinolones have not been tested in children despite their wide spectrum of in vitro activity and efficacy, because of an observed damage to cartilage in young animals. However, in some cases they may be life-saving. We present three pediatric patients with life threatening infections in whom the fluoroquinolones were used when other antibiotics failed: A seven-year-old boy with meningitis due to multiresistant Acinetobacter calcoaceticus, a three-year-old boy with Job's syndrome with line sepsis due to Staphylococcus epidermidis and a four month-old boy with agammaglobulinemia with mixed infection due to Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter spp. All three children were cured of their infections.

Comparative analysis of the structures of the outer membrane protein P1 genes from major clones of Haemophilus influenzae type b

P1 outer membrane proteins from Haemophilus influenzae type b are heterogeneous antigenically and with respect to apparent molecular weight in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. For determination of the molecular basis for the differences in the P1 proteins, the genes for the P1 proteins from strain 1613, representative of outer membrane protein subtype 3L, and strain 8358, representative of outer membrane protein subtype 6U, were cloned, sequenced, and compared with the previously reported gene for the P1 protein from strain MinnA, a strain with the outer membrane protein subtype 1H. These prototype strains are representatives of the three major clonal families of H. influenzae type b responsible for invasive disease in diverse areas of the world. The nucleotide sequences of the P1 genes from strains 1613 and 8358 were 94 and 90% identical to the MinnA sequence, respectively. The derived amino acid sequences were 91 and 86% identical, respectively. Heterogeneity between the MinnA and 1613 proteins was largely localized to two short variable regions; the protein from strain 8538 contained a third variable region not observed in the other P1 proteins. Thus, the outer membrane protein P1 genes are highly conserved; the variable regions may code for the previously demonstrated strain-specific antigenic determinants.