Clinical, genetic and environmental factors associated with congenital vertebral malformations.

Congenital vertebral malformations (CVM) pose a significant health problem because they can be associated with spinal deformities, such as congenital scoliosis and kyphosis, in addition to various syndromes and other congenital malformations. Additional information remains to be learned regarding the natural history of congenital scoliosis and related health problems. Although significant progress has been made in understanding the process of somite formation, which gives rise to vertebral bodies, there is a wide gap in our understanding of how genetic factors contribute to CVM development. Maternal diabetes during pregnancy most commonly contributes to the occurrence of CVM, followed by other factors such as hypoxia and anticonvulsant medications. This review highlights several emerging clinical issues related to CVM, including pulmonary and orthopedic outcome in congenital scoliosis. Recent breakthroughs in genetics related to gene and environment interactions associated with CVM development are discussed. The Klippel-Feil syndrome which is associated with cervical segmentation abnormalities is illustrated as an example in which animal models, such as the zebrafish, can be utilized to provide functional evidence of pathogenicity of identified mutations.

The role of cigarette smoking and statins in the development of postmenopausal osteoporosis: a pilot study utilizing the Marshfield Clinic Personalized Medicine Cohort.

SUMMARY: A cohort of postmenopausal osteoporotic females and controls with normal bone mineral density, the interleukin 6 (IL6) -634G > C (rs1800796) C allele of the promoter region showed association with osteoporosis. The lipoprotein receptor-related protein 5 (LRP5) gene showed association between C135242T C/T alleles and osteoporosis only in smokers, suggesting a role for environmental interaction. INTRODUCTION: A nested case-control study within a population-based cohort was undertaken to assess the relative impact of cigarette smoking, statin use, genetic polymorphisms, and one-way interaction of these factors on development of osteoporosis in postmenopausal women. METHODS: Genotyping of 14 single-nucleotide polymorphisms (SNPs) corresponding to vitamin D receptor gene, estrogen receptor 1, collagen type 1 alpha 1, IL6, transcription growth factor beta, apolipoprotein E, and LRP5 genes was performed in cases (n = 309) with osteoporosis and controls (n = 293) with normal bone mineral density drawn from a homogeneous Caucasian population. SNPs were chosen based on known functional consequences or prior evidence for association and genotyped using matrix-assisted laser desorption ionization time-of-flight technology. RESULTS: Cases differed from controls relative to body mass index, age, and smoking but not statin use. After adjusting for age, the IL6 -634G > C (rs1800796) allele showed association with osteoporosis (odds ratio (OR) for CC + CG = 2.51, p = 0.0047)), independent of statin use or smoking status. On stratification for smoking, association with LRP5 C135242T (rs545382) and osteoporosis emerged (OR 2.8 in smokers for CT alleles, p = 0.03)), suggestive of potential environmental interaction. CONCLUSION: Evidence suggested a role for genetic variation in IL6 and LRP5 in conferring risk for osteoporosis in Caucasian women, with the latter manifest only in smokers.

Healthy People 2010 disease prevalence in the Marshfield Clinic Personalized Medicine Research Project cohort: opportunities for public health genomic research.

OBJECTIVES: The purpose of this study was to estimate the prevalence of Healthy People 2010 disease conditions in a large population-based cohort in central Wisconsin (WI, USA) and to consider how these conditions can be prioritized for research based on the use of healthcare services, the prevalence of various disease states and the resulting study power. METHODS: Healthy People 2010 diagnoses were estimated for participants in the Personalized Medicine Research Project (PMRP), a large population-based biobank for residents aged 18 years and older living in central Wisconsin. By interrogating the electronic medical record, three parameters were calculated for each diagnosis: mean number of concomitant diagnoses, mean number of annual clinic visits before diagnosis and mean number of clinic visits after diagnosis. RESULTS: A total of 18,239 adults enrolled in PMRP from September 2002 to May 2005 and were included in the study. They had a mean age of 49 years (standard deviation: 18.5), ranging from 18-98 years; 57% were female. At least one Healthy People 2010 disease was diagnosed in 86.4% of the participants; 13.6% had never been diagnosed with any of these conditions. The median number of diagnoses per subject was three (range: 1-15). The median number of annual visits after diagnosis was lowest for chronic obstructive pulmonary disease (9.1) and highest for sleep apnea (17.9). Subjects with a diabetic retinopathy diagnosis had the highest number of concomitant diagnoses (mean: 6.8). DISCUSSION: All of the diseases within the Healthy People 2010 list are purported to have at least some genetic component, with the exception of injuries. The PMRP cohort is large enough that diseases of public health importance can be studied in the context of a variety of clinical and environmental covariates. This database is being developed as a national resource and is particularly useful where the estimated disease prevalence is 5% or greater. For less common diseases, additional cases can be recruited from throughout the Marshfield Clinic system of care, with population-based controls selected from the main PMRP study cohort.

Widened clinical spectrum of the Q128P MECP2 mutation in Rett syndrome.

CASE REPORT: We describe a female patient with Arnold Chiari type I malformation, atypical Rett syndrome characterized by postnatal onset microcephaly, stereotypic hand movements, ataxia, severe developmental delay, intractable tonic-clonic seizures, and a MECP2 mutation with a unique set of clinical findings. Implementation of a ketogenic diet resulted in decreased seizure activity and an improvement in the patient's degree of social relatedness with her family members. DISCUSSION: An early diagnosis of Rett syndrome allows families to maximize utilization of existing treatment modalities and seek appropriate genetic counseling and prenatal diagnoses. This case also provides further evidence for the treatment benefit of ketogenic diets for seizures in patients with Rett syndrome.

An analysis of PAX1 in the development of vertebral malformations.

An analysis of PAX1 in the development of vertebral malformations. Due to the sporadic occurrence of congenital vertebral malformations, traditional linkage approaches to identify genes associated with human vertebral development are not possible. We therefore identified PAX1 as a candidate gene in vertebral malformations and congenital scoliosis due to its mutation in the undulated mouse. We performed DNA sequence analysis of the PAX1 gene in a series of 48 patients with congenital vertebral malformations, collectively spanning the entire vertebral column length. DNA sequence coding variants were identified in the heterozygous state in exon 4 in two male patients with thoracic vertebral malformations. One patient had T9 hypoplasia, T12 hemivertebrae and absent T10 pedicle, incomplete fusion of T7 posterior elements, ventricular septal defect, and polydactyly. This patient had a CCC (Pro)-->CTC (Leu) change at amino acid 410. This variant was not observed in 180 chromosomes tested in the National Institute of Environmental Health Sciences (NIEHS) single nucleotide polymorphism (SNP) database and occurred at a frequency of 0.3% in a diversity panel of 1066 human samples. The second patient had a T11 wedge vertebra and a missense mutation at amino acid 413 corresponding to CCA (Pro)-->CTA (Leu). This particular variant has been reported to occur in one of 164 chromosomes in the NIEHS SNP database and was found to occur with a similar frequency of 0.8% in a diversity panel of 1066 human samples. Although each patient's mother was clinically asymptomatic and heterozygous for the respective variant allele, the possibility that these sequence variants have clinical significance is not excluded.

Prevalence and patterns of presentation of genetic disorders in a pediatric emergency department.

OBJECTIVES: To determine the prevalence and patterns of presentation of previously diagnosed and of suspected genetic disorders among pediatric emergency department (ED) visits to a hospital that serves an inner-city population. PATIENTS AND METHODS: A retrospective review of 15,258 pediatric (<18 years old) ED visits at Lincoln Medical and Mental Health Center was undertaken for visits that occurred between October 1998 and February 1999. Suspected genetic disorders, classified into chromosomal, single gene, multifactorial, and other syndromic categories, were recorded. RESULTS: Of 15,258 visits reviewed, 2839 visits (18.6%) were by patients who had known or suspected genetic disorders. Previously diagnosed genetic disorders were documented in 80 visits (2.8%). Of these, 69 visits (86.2%) were related to single gene disorders, 3 (3.8%) to chromosomal disorders, 6 (7.5%) to multifactorial disorders, and 2 (2.5%) to disorders in the "other" category. Of these 80 visits, 59 (74%) were associated with sickle cell disease. The remaining 2759 visits (97.2%) were associated with complaints or diagnoses that suggested the possibility of an underlying genetic disorder requiring further evaluation and diagnostic work-up. CONCLUSIONS: Pediatric patients with known or suspected genetic disorders are frequently treated in EDs. Awareness of underlying genetic disorders facilitates diagnostic evaluation, treatment planning, and referral to a genetics clinic for counseling.

Evaluation of growth and hormonal status in patients referred to the International Fanconi Anemia Registry.

OBJECTIVES: 1) To determine the extent of short stature in patients with Fanconi anemia (FA); 2) to determine the extent and nature of endocrinopathy in FA; 3) to assess the impact on height of any endocrinopathies in these patients; and 4) to study the correlation, if any, between height, endocrinopathy, and FA complementation group. STUDY DESIGN: Fifty-four patients with FA, 30 males and 24 females from 47 unrelated families, were prospectively evaluated in a Pediatric Clinical Research Center. The patients ranged in age from 0.1-31.9 years, with the mean age at assessment 8.6 years. RESULTS: Endocrine abnormalities were found in 44 of the 54 FA patients tested (81%), including short stature, growth hormone (GH) insufficiency, hypothyroidism, glucose intolerance, hyperinsulinism, and/or overt diabetes mellitus. Twenty-one of 48 (44%) participants had a subnormal response to GH stimulation; 19 of 53 (36%) had overt or compensated hypothyroidism, while 8 of 40 participants had reduced thyroid-hormone binding. Two patients were diabetic at the time of study; impaired glucose tolerance was found in 8 of 40 patients (25%), but most surprisingly, hyperinsulinemia was present in 28 of 39 (72%) participants tested. Significantly, spontaneous overnight GH secretion was abnormal in all patients tested (n = 13). In addition, participants demonstrated a tendency toward primary hypothyroidism with serum tetraiodothyronine levels at the lower range of normal, while also having thyrotropin (thyroid-stimulating hormone) levels at the high end of normal. Sixteen patients were assigned to FA complementation group A, (FA-A), 12 to FA-C, and 5 to FA-G; 10 of the 12 participants in FA-C were homozygous for a mutation in the intron-4 donor splice site of the FANCC gene. Patients in groups FA-A and FA-G were relatively taller than the group as a whole (but still below the mean for the general population), whereas those in FA-C had a significantly reduced height for age. GH response to stimulation testing was most consistently normal in participants from FA-G, but this did not reach statistical significance. The tendency toward hypothyroidism was more pronounced in participants belonging to complementation groups FA-C and FA-G, whereas insulin resistance was most evident in patients in FA-G, and least evident in those in FA-C. Short stature was a very common finding among the patients with a mean height >2 standard deviations below the reference mean (standard deviation score: -2.35 +/- 0.28). Patients with subnormal GH response and those with overt or compensated hypothyroidism were shorter than the group with no endocrinopathies. The heights of those participants with glucose or insulin abnormalities were less severely affected than those of normoglycemic, normoinsulinemic participants, although all were significantly below the normal mean. The mean height standard deviation score of patients with entirely normal endocrine function was also >2 standard deviations below the normal mean, demonstrating that short stature is an inherent feature of FA. CONCLUSION: Endocrinopathies are a common feature of FA, primarily manifesting as glucose/insulin abnormalities, GH insufficiency, and hypothyroidism. Although short stature is a well-recognized feature of FA, 23 patients (43%) were within 2 standard deviations, and 5 of these (9% of the total) were actually above the mean for height for the general population. Those patients with endocrine dysfunction are more likely to have short stature. These data indicate that short stature is an integral feature of FA, but that superimposed endocrinopathies further impact on growth. The demonstration of abnormal endogenous GH secretion may demonstrate an underlying hypothalamic-pituitary dysfunction that results in poor growth.

The incidence of protrusio acetabuli in Marfan's syndrome and its relationship to bone mineral density.

Twenty-one patients with Marfan's syndrome participated in a study to assess the incidence of and radiographic measurements significant for protrusio acetabuli. Our data show that the incidence of protrusio acetabuli in Marfan's syndrome is 31%. The most sensitive radiographic parameter to determine protrusio acetabuli is crossing of the acetabular line by the iliopectineal line. The presence of protrusio in Marfan's syndrome was not related to the bone mineral content of the hip and pelvis. Protrusio acetabuli in Marfan syndrome's also did not correlate with clinical symptoms. Based on our results, the presence of protrusio acetabuli alone is not an indication for early surgical intervention.

A genomic approach to scoliosis pathogenesis.

Genetic predisposition contributes to scoliosis in humans. Two syndromes of primary scoliosis occur--congenital scoliosis, which presents at birth, often associated with other abnormalities, and idiopathic scoliosis which becomes apparent between infancy and adolescence. Little is known regarding the genetic transmission of scoliosis risk. Data gleaned from mouse mutations provide a valuable supplement to human family studies. More than 50 mouse mutations include scoliosis, kyphosis, or tail kinks as a phenotype; the locations of the human homologues for 28 of these can be predicted on the basis of synteny conservation. Some mouse mutations are either more penetrant or more fully expressed in one sex. The mouse data provide a basis both for optimism and for caution in understanding human scoliosis. Mouse models provide insight into mechanisms underlying spinal curvature and help direct searches for genes important in human disease. Four types of defects account for most mouse scoliosis: defects of cell-cell communication, intracellular signal transduction, matrix protein synthesis, and matrix protein metabolism. Mouse data suggest that at least two types of heterogeneity complicate genetic analysis: locus heterogeneity, in which lesions of distinct genes lead to a similar phenotype, and allelic heterogeneity, in which the phenotypes arising from alleles of a single gene differ. By focusing initial studies on multiplex families with apparent simple Mendelian inheritance the effect of heterogeneity is minimized.

Synteny-defined candidate genes for congenital and idiopathic scoliosis.

Idiopathic scoliosis (IS) is a common but poorly understood syndrome. Congenital scoliosis (CS) is less common but comparably unexplored. Previous studies suggest that each has a significant genetic component. However, the occurrence of scoliosis in the presence of other hereditary connective tissue syndromes raises the possibility that IS and CS are in fact a heterogeneous group of disorders with varied pathogenetic mechanisms. Mouse mutations have proven informative in identifying genes that are important in the development of the musculoskeletal system and provided important mechanistic insights regarding their roles in human disease. We sought to identify candidate genes for human IS and CS by reviewing mouse mutations with phenotypes affecting the axial skeleton. We performed a systematic review using the Mouse Genome Database (MGD), the Genome Database (GDB), and the Online Mendelian Inheritance in Man (OMIM) world-wide-web sites with additional searches performed based on the results of this initial search. We identified approximately 400 mouse mutations, reviewed approximately 250 of these for vertebral phenotypes, assessed 45 of these for synteny conservation between mouse and man, and identified 28 mouse mutations for which 29 credible candidates for human scoliosis could be identified based on mouse phenotypic and mapping data. For each of these, we have synthesized information about the mouse mutant phenotype, mapping data, information regarding molecular pathogenesis when a specific causative gene has been identified, and information regarding plausible candidates based on map position when the causative gene has not been identified. Among these were three loci for which the mutant gene had been identified and the human homologue was known. Some of the mouse mutants have phenotypes similar to human syndromes.

New recessive syndrome characterized by increased chromosomal breakage and several findings which overlap with Fanconi anemia.

We describe four cases with several findings of Fanconi anemia (FA), but without hypersensitivity to DNA cross-linking that is the distinguishing characteristic of FA. Two of the cases are male and female sibs of Hispanic origin, age 6 years and 11 months, respectively. Both have short stature, failure to thrive, absent thumbs, short palpebral fissures, and skin pigmentation abnormalities. The girl also has developmental "dysplasia" of her hips. Presently, both siblings are hematologically normal. Elevated baseline chromosome breakage was observed in the boy, but not in the girl. Neither sib showed elevated diepoxybutane (DEB)-induced chromosomal breakage. In a subsequent pregnancy, prenatal studies showed slightly elevated baseline and DEB induced chromosome breakage (greater than normal, but lower than the established range for FA). The fetus had intrauterine growth retardation and an absent right thumb. A review of cases referred to the International Fanconi Anemia Registry for DEB testing showed one additional case with similar findings. That patient, a girl, of Caucasian English ancestry, age 14 years, had short stature, a history of failure to thrive, skin pigmentation abnormalities, absent right thumb, hypoplastic left thumb, and hydrocephalus that resolved spontaneously. Elevated baseline chromosome breakage was observed in skin fibroblasts but not in lymphocytes. We postulate that these cases represent a previously undescribed autosomal recessive syndrome. These and other previously reported cases provide evidence for alternative genetic mechanisms that may result in developmental anomalies similar to those seen in FA.

Phenotypic consequences of mutations in the Fanconi anemia FAC gene: an International Fanconi Anemia Registry study.

Fanconi anemia (FA) is a genetically and phenotypically heterogeneous disorder defined by cellular hypersensitivity to DNA cross-linking agents; mutations in the gene defective in FA complementation group C, FAC, are responsible for the syndrome in a subset of patients. We have performed an analysis of the clinical effects of specific mutations in the FAC gene. Using the amplification refractory mutation system assays that we developed to rapidly detect FAC mutations, at least one mutated copy of the FAC gene was identified in 59 FA patients from the International Fanconi Anemia Registry (IFAR). This represents 15% of the 397 FA patients tested. FA-C patients were divided into three subgroups based on results of a genotype-phenotype analysis using the Cox proportional hazards model: (1) patients with the IVS4 mutation (n = 26); (2) patients with at least one exon 14 mutation (R548X or L554P) (n = 16); and (3) patients with at least one exon 1 mutation (322delG or Q13X) and no known exon 14 mutation (n = 17). Kaplan-Meier analysis shows that IVS4 or exon 14 mutations define poor risk subgroups, as they are associated with significantly earlier onset of hematologic abnormalities and poorer survival compared to exon 1 patients and to the non-FA-C IFAR population. There was no direct correlation between the degree of cellular hypersensitivity to the clastogenic effect of diepoxybutane and severity of clinical phenotype. Sixteen of the 59 FA-C patients (27%) have developed acute myelogenous leukemia. Thirteen of these patients have died; AML was the cause of death in 46% of the expired FA-C patients. This study enables us to define this clinically heterogeneous disorder genotypically to better predict clinical outcome and aid decision-making regarding major therapeutic modalities for a subset of FA patients.

Diagnosis of Fanconi anemia in patients without congenital malformations: an international Fanconi Anemia Registry Study.

Data were analyzed from 419 Fanconi anemia (FA) patients enrolled in the American Registry of the International Fanconi Anemia Registry (IFAR) to determine whether Fanconi anemia (FA) patients without major congenital malformations (CM) have distinguishing characteristics that can lead to an earlier diagnosis. These included 377 patients reported by physicians to the IFAR and 42 patients examined by us. The number of FA patients in each group without CM was 128 and 16, respectively; one third of all patients lacked CM. We found that height, weight, and head circumference were < or = 5th centile in 26.6%, 18.0%, and 8.6% of FA patients without CM referred to the IFAR, and in 43.8%, 25.0%, and 43.8% of FA patients without CM examined by us. Minor anomalies were reported in 9.4% of FA patients without CM referred to the IFAR and 100% of FA patients without CM examined by us. Most FA patients without CM have alterations in growth parameters, skin pigmentation abnormalities, or microphthalmia. Increased awareness of the complete spectrum of FA by clinicians will enable an earlier diagnosis to be made.

Fragile X syndrome in two siblings with major congenital malformations.

We report on 2 brothers with both fragile X and VACTERL-H syndrome. The first sibling, age 5, had bilateral cleft lip and palate, ventricular septal defect, and a hypoplastic thumb. The second sibling, age 2 1/2, had a trachesophageal fistula, esophageal atresia, and vertebral abnormality. High-resolution chromosome analysis showed a 46, XY chromosome constitution in both siblings. By PCR and Southern blot analysis, the siblings were found to have large triplet repeat expansions in the fragile X gene (FMR 1) and both had methylation mosaicism. Enzyme kinetic studies of iduronate sulfatase demonstrated a two-fold increase in activity in the first sib as compared to the second. Possible mechanisms through which the fragile X mutation can cause down-regulation of adjacent loci are discussed.

Congenital fusion of the fourth and fifth metacarpals associated with primary gonadal failure.

Congenital fusion of the fourth and fifth metacarpals is described in a male infant and his maternal grandfather. Primary gonadal failure, which is present in the infant, has not been noted in previously, reported cases. The pedigree in this family is compatible with X-linked recessive or autosomal dominant inheritance with incomplete penetrance.

The need for more accurate and timely diagnosis in Fanconi anemia: a report from the International Fanconi Anemia Registry.

OBJECTIVE: The objective of this study was to address the need for early diagnosis of Fanconi anemia (FA), an autosomal recessive chromosomal instability syndrome characterized by a unique cellular hypersensitivity to DNA cross-linking agents, such as diepoxybutane, and by a high risk of malignancies. METHODS: We analyzed data from 370 FA patients enrolled in the American Registry of the International FA Registry. Of these individuals, 220 had congenital malformations; the rest were ascertained based on hematologic abnormalities only or on clinical evaluation and screening following the diagnosis of an affected family member. The probands noted to have congenital malformations at the time of diagnosis were classified into two groups on the basis of their clinical presentation: (1) patients manifesting both congenital malformations and hematologic abnormalities (159 individuals); (2) patients manifesting congenital malformations only (61 individuals). RESULTS: The mean age of diagnosis was 6.6 years and 1.1 years for Groups 1 and 2, respectively. Thus, the majority of FA patients with congenital malformations were not diagnosed until after the onset of hematologic abnormalities. We also report central nervous system, gastrointestinal, and skeletal malformations which previously have not been included as part of the FA phenotype. Our review of the patients enrolled in the International FA Registry indicates that the FA phenotype is more variable than recognized previously. CONCLUSIONS: Testing for sensitivity to diepoxybutane to rule out a diagnosis of FA needs to be applied more widely in patients with congenital malformations. All siblings of affected probands also should have testing, because a lack of concordance of phenotype in affected siblings makes clinical diagnosis unreliable even within sibships. A more timely diagnosis of FA in the preanemic phase is needed to implement appropriate therapy and to enable parents to make informed reproductive decisions.

Fanconi anemia: a model for genetic causes of abnormal brain development.

Fanconi anemia is an autosomal recessive disease resulting in bone-marrow failure, phenotypical abnormalities and predisposition to malignancy. The authors reviewed 257 clinical and neuropathology results from the International Fanconi Anemia Registry at The Rockefeller University. Two patients had hydrocephalus and ventriculoperitoneal shunts. Of 15 neuropathology reports, 10 found CNS abnormalities, with the most common--ventriculomegaly--seen in six, two of whom required shunts. Aqueductal stenosis, agenesis of the corpus callosum and septum pellucidum, and holoprosencephaly were found. The authors conclude that neurological derangements are probably more common in Fanconi anemia than previously recognised. Fanconi anemia cells in culture are highly sensitive to oxidative stress and alkylating agents; Fanconi anemia may provide a model for a genetic disorder potentially predisposing to environmental insults.

Determination of delta-aminolevulinate dehydratase activity by a specific fluorometric coupled-enzyme assay.

A coupled-enzyme assay for the specific and sensitive determination of delta-aminolevulinate dehydratase activity has been developed. The assay specifically measured picomole quantities of the product, porphobilinogen, by its enzymatic conversion to uroporphyrinogen I and the fluorometric detection of oxidized uroporphyrin I. The coupled-enzyme assay was linear with time and protein concentration and required less than 3 h for 20 individual determinations. Under the standard assay conditions, 10 to 100 pmol of uroporphyrin I was reliably measured, representing 0.085 to 0.850 nmol/h of delta-aminolevulinate dehydratase activity per assay. In addition, the fluorometric assay was more sensitive than either the standard or the semimicro colorimetric methods. The specificity, rapidity, and sensitivity of this new fluorometric method facilitates the reliable determination of low levels of aminolevulinate dehydratase activity in small amounts of crude tissue homogenates or in cultured cells.

Regional gene assignment of human porphobilinogen deaminase and esterase A4 to chromosome 11q23 leads to 11qter.

The regional gene assignments for human porphobilinogen deaminase (PBGD; EC 4.3.1.8) and esterase A4 (ESA4; EC3.1.1.1) chromosome 11 have been determined with somatic cell hybridization and immunologic, electrophoretic, and cytogenetic techniques. Dimethyl sulfoxide-induced erythroid differentiation of hybrid clones derived from the fusion of tetraploid Friend murine erythroleukemia (2S MEL) cells deficient in thymidine kinase and human Lesch--Nyhan fibroblasts (HLN) deficient in hypoxanthine phosphoribosyltransferase (HPRT-; EC 2.4.2.8) were examined for expression of human PBGD, ESA4, and lactate dehydrogenase A (LDHA; EC 1.1.1.27). Human PBGD was detected by rocket immunoelectrophoresis with rabbit anti-human PBGD IgG and by isoelectric focusing. The human chromosome complement of each clone was determined by cytogenetic and enzyme marker analyses. Of the five primary 2S MEL--HLN clones examined, three were positive for human PBGD. These were subcloned to yield a total of 10 secondary, tertiary, or quaternary clones. Analyses of these subclones permitted the regional assignment of human PBGD and ESA4 to the long arm of chromosome 11. Finer regional assignment of the loci for human PBGD and ESA4 was facilitated when two 2S MEL (HPRT-)--human fibroblast (HX/11) hybrids, each containing the X chromosome--autosome translocation (der11), t(X;11)(q25-26;q23) as the only human chromosome, were examined for expression of human PBGD, ESA4, and LDHA. One clone, HX/11-2, contained the intact X/11 translocated chromosome; in the other, HX/11-3, 11p was deleted, and the human X/11 derivative was translocated onto a mouse chromosome. HX/11-2 expressed human LDHA, but HX/11-3 did not, verifying that the latter human 11/X derivative did not include 11pter leads to 11p12; PBGD and ESA4 were not detected in either hybrid. These results confirm the location of the gene for human PBGD on chromosome 11 and establish the assignment of the loci for PBGD and ESA4 in the region 11q23 leads to 11qter.