Ecosystem engineers: feedback and population dynamics.

All organisms alter their abiotic environment, but ecosystem engineers are species with abiotic effects that may have to be explicitly accounted for when making predictions about population and community dynamics. The goal of this analysis is to identify those conditions in which engineering leads to population dynamics that are qualitatively different than one would predict using models that incorporate only biotic interactions. We present a simple model coupling an ecosystem engineer and the abiotic environment. We assume that the engineer alters environmental conditions at a rate dependent on engineer density and that the environment decays back to original conditions at an exponential rate. We determine when the feedback to population dynamics through environmental state can lead to altered equilibrium densities, bistability, or runaway growth of the engineer population. The conditions leading to changes in dynamics, such as susceptibility of a system to engineering or alteration of density-dependent and density-independent controls, define cases in which the engineering concept is essential for ecological understanding.

Demyelination of the brain is associated with methionine adenosyltransferase I/III deficiency.

Individuals deficient in hepatic methionine adenosyltransferase (MAT) activity (MAT I/III deficiency) have been demonstrated to contain mutations in the gene (MATA1) that encodes the major hepatic forms, MAT I and III. MAT I/III deficiency is characterized by isolated persistent hypermethioninemia and, in some cases, unusual breath odor. Most individuals with isolated hypermethioninemia have been free of major clinical difficulties. Therefore a definitive diagnosis of MAT I/III deficiency, which requires hepatic biopsy, is not routinely made. However, two individuals with isolated hypermethioninemia have developed abnormal neurological problems, including brain demyelination, suggesting that MAT I/III deficiency can be deleterious. In the present study we have examined the MATA1 gene of eight hypermethioninemic individuals, including the two with demyelination of the brain. Mutations that abolish or reduce the MAT activity were detected in the MATA1 gene of all eight individuals. Both patients with demyelination are homozygous for mutations that alter the reading frame of the encoded protein such that the predicted MATalpha1 subunits are truncated and enzymatically inactive. The product of MAT, S-adenosylmethionine (AdoMet), is the major methyl donor for a large number of biologically important compounds including the two major myelin phospholipids, phosphatidylcholine and sphingomyelin. Both are synthesized primarily in the liver. Our findings demonstrate that isolated persistent hypermethioninemia is a marker of MAT I/III deficiency, and that complete lack of MAT I/III activity can lead to neurological abnormalities. Therefore, a DNA-based diagnosis should be performed for individuals with isolated hypermethioninemia to assess if therapy aimed at the prevention of neurological manifestations is warranted.

Evolutionarily Stable Strategies for Consuming a Structured Resource.

A general consumer-resource model assuming discrete consumers and a continuously structured resource is examined. We study two foraging behaviors, which lead to fixed and flexible patch residence times, in conjunction with a simple consumer energetics model linking resource consumption, foraging behavior, and metabolic costs. Results indicate a single, evolutionarily stable foraging strategy for fixed and flexible foraging in a nonspatial environment, but flexible foraging in a spatial environment leads to consumer grouping, which affects the resource distribution such that no single foraging strategy can exclude all other strategies. This evolutionarily stable coexistence of multiple foraging strategies may help explain a dichotomous pattern observed in a wide variety of natural systems.

Oral phenylalanine loading in dopa-responsive dystonia: a possible diagnostic test.

To determine if there is abnormal phenylalanine and biopterin metabolism in patients with dopa-responsive dystonia (DRD), we measured plasma levels of phenylalanine, tyrosine, biopterin, and neopterin at baseline, and 1, 2, 4, and 6 hours after an oral phenylalanine load (100 mg/kg). Seven adults with DRD, two severely affected children with DRD, and nine adult controls were studied. All patients had phenylalanine and tyrosine concentrations within the normal range at baseline. In the adult patients, phenylalanine levels were higher than in controls at 2, 4, and 6 hours post-load (p < 0.0005); tyrosine concentrations were lower than control levels at 1, 2, and 4 hours post-load (p < 0.05). Phenylalanine to tyrosine ratios were elevated in patients at all times post-load (p < 0.0005). Biopterin levels in the patients were decreased at baseline and 1, 2, and 4 hours post-load (p < 0.005). Pretreatment with tetrahydrobiopterin (7.5 mg/kg) normalized phenylalanine and tyrosine profiles in two adult patients. In the children with DRD, phenylalanine to tyrosine ratios were slightly elevated at baseline. Following phenylalanine loading, the phenylalanine profiles were similar to those seen in the adult patients but there was no elevation in plasma tyrosine. Baseline biopterin levels were lower in the children with DRD than in the adult patients or the controls and there was no increase in biopterin post-load. In both the children and adults with DRD, neopterin concentrations did not differ from control values at baseline or after phenylalanine load. The results are consistent with decreased liver phenylalanine hydroxylase activity due to defective synthesis of tetrahydrobiopterin in patients with DRD. The findings show that a phenylalanine load may be useful in the diagnosis of this disorder.

Familial spontaneous pneumothorax.

A family is described in which four persons in three generations suffered spontaneous pneumothoraces: a newborn, an infant, an adolescent, and an adult. Review of the literature reveals 61 reports of familial spontaneous pneumothorax in 22 families. The ratio of male to female cases is approximately 1.8. Affected parents and affected children (including affected fathers and sons) are seen in ten families, while affected siblings with unaffected parents are noted in 13 families. Consanguinity has not been reported. Although autosomal dominant inheritance has been suggested as an explanation of familial spontaneous pneumothorax, available pedigree data are not adequate for statistical analysis. Physicians should be aware of the familial occurrence of spontaneous pneumothorax so that members of such families may be appropriately managed when problems arise.

The Langer-Giedion syndrome: report of a 22-year old woman.

A 22-year-old woman with the Langer-Giedion syndrome and delayed puberty is presented. Pertinent features include a bulbous nose, sparse hair, protruding ears, multiple cartilaginous exostoses, cone-shaped phalangeal epiphyses, short stature, microcephaly, and mental retardation. She is the oldest patient thus far described with this condition, and is compared to the ten previously published cases. The clinical course of patients with the Langer-Giedion syndrome and the possibility of malignant change in the exostoses have not been established.

Selection for intermediate mortality and reproduction rates in a spatially structured population.

How local interactions influence both population and evolutionary dynamics is currently a key topic in theoretical ecology. We use a 'well-mixed' analytical model and spatially explicit individual-based models to investigate a system where a population is subject to rare disturbance events. The disturbance can only propagate through regions of the population where the density of individuals is sufficiently high and individuals affected by the disturbance die shortly after. We find that populations where individuals are sessile often exhibit very different dynamic behaviour when compared to populations where individuals are mobile and spatially well mixed. When mutations are allowed which affect either offspring birth rates or mortality rates, the well-mixed populations always evolve to a state where a single disturbance event leads to extinction. Populations often persist substantially longer if individuals are sessile and they disperse their offspring locally. We also find that for sessile populations selection may favour short-lived individuals with limited offspring production. Population dynamics are found to be strongly influenced by the host characters that are evolving and the rate at which host variation is introduced into the system.

Brief clinical report: early recognition of the Coffin-Lowry syndrome.

We report a 2-year-old male infant with the Coffin-Lowry syndrome, and describe the change in his clinical and radiographic manifestations during the first 2 years of life. Review of published cases of the Coffin-Lowry syndrome indicates that these manifestations are progressive, and that all of the associated characteristics may not be apparent in early childhood. The importance of continued evaluations of these patients and examination of relatives for mild manifestations is emphasized.

A "new" skeletal dysplasia in two unrelated boys.

We report on 2 unrelated boys with similar physical and radiographic findings that may represent a "new" skeletal dysplasia. Findings in common include early speech delay, short stature, frontal bossing with a depression over the metopic suture, a narrow nasal root with beaked nose, midfacial hypoplasia with relatively prominent eyes, and brachydactyly with blunt fingers. Radiographic findings include mild irregularities of the vertebral bodies, hypoplasia of the odontoid process, short phalanges with increased distal width, coning and sclerosis of several epiphyses, and overtubulation of the long bones. Although these patients share some manifestations with the floating-harbor syndrome (Robinson et al.: J Pediatr 113:703-706, 1988), their radiographic changes are distinctive and are not suggestive of a recognized skeletal dysplasia syndrome.

Absent pituitary gland in two brothers with an oral-facial-digital syndrome resembling OFDS II and VI: a new type of OFDS?

The oral-facial-digital syndromes (OFDS) comprise a group of heterogeneous genetic disorders. Considerable clinical overlap exists within the nine described types [Toriello, Clin Dysmorph 2:95-105, 1993], and with other entities such as Pallister-Hall (PH) syndrome and hydrolethalus syndrome, leading to difficulties in the classification of OFDS. We report on two brothers with findings overlapping OFDS II, VI, and Pallister-Hall syndrome who had congenital absence of the pituitary gland. This may represent a new type of OFDS or, alternatively, an example of phenotypic variability within the OFDS. It also emphasizes that agenesis of the pituitary gland can occur in a variety of syndromes with midline defects.

Apparent Ruvalcaba syndrome with genitourinary abnormalities.

The Ruvalcaba syndrome is a rare malformation syndrome characterized by skeletal dysplasia, facial anomalies, and mental retardation. We report on a 22-year-old woman with severe growth and mental retardation and numerous manifestations characteristic of the Ruvalcaba syndrome. In addition, she has several anomalies not previously described in the Ruvalcaba syndrome, including upslanting palpebral fissures, torus palatinus, hiatal hernia with gastroesophageal reflux, recurrent respiratory infections, pectus excavatum, equinovarous deformity, hypotonia, unilateral renal hypoplasia, an accessory ovary, and atretic fallopian tube. Review of published reports of Ruvalcaba syndrome confirms variability of the clinical and radiographic changes. Findings present in at least 50% of reported patients include mental retardation, short stature, pubertal delay, an abnormal nose (usually beaked) with hypoplastic nasal alae, microstomia with narrow maxilla, thin upper lip vermilion, broad hips, small hands, joint limitation, short fingers and toes, and vertebral abnormalities. Because 5 of the reported patients had renal abnormalities, a renal ultrasound or contrast study is indicated in the evaluation of these patients. Additional reports, particular from multiplex families, will be important to better characterize this syndrome.

Constellation of congenital abnormalities in an infant: a new syndrome or tissue-specific mosaicism for trisomy 18?

A newborn infant born to consanguineous (first cousin) parents was noted to have complex congenital heart defect and minor anomalies suggestive of trisomy 18. Blood lymphocyte and skin fibroblast karyotypes were normal. He died in the neonatal period of postoperative complications. On interphase fluorescence in-situ hybridization (FISH) using autopsy specimens, a significant number of cells in the liver (17%) were trisomic for chromosome 18, compared to normal control liver tissue. However, interphase FISH analyses of blood lymphocytes, skin fibroblasts, and kidney tissue were normal. It is our opinion that this apparent mosaicism for trisomy 18 in the patient's liver may be spurious, though it brings into focus the issue of possible tissue/organ-specific mosaicism. The anomalies in this infant do not resemble a previously described malformation syndrome. Parental consanguinity raises the possibility that this represents a new autosomal recessive malformation syndrome.

Deletion (14) (q24.3q32.1): evidence for a distinct clinical phenotype.

We report on a 4-year-old girl with distinctive facial features (redundant skin, bushy eyebrows, narrow palpebral fissures, short, upturned nose, epicanthal folds, and a long upper lip with well-defined philtrum) who has an interstitial deletion of chromosome 14 including band 14q31, designated as 46,XX,del(14)(pter-->q24.3::q32.1-->qter). Comparison with previously reported patients with deletions of 14q involving band 14q31 suggests that there is a distinctive clinical phenotype associated with this deletion. Our patient had dental abnormalities (3 maxillary and 3 mandibular incisors) not described in the other patients.

"New" ectodermal dysplasia syndrome with distinctive facial appearance and preaxial polydactyly of feet.

We describe a 2-year-old girl with virtual absence of body and scalp hair, rounded nails, thin dental enamel, preaxial polydactyly of feet, and unusual facial appearance. This combination of findings is not similar to that of any of the previously described ectodermal dysplasia syndromes and may represent a new disorder.

Holoprosencephaly and interstitial deletion of 2(p2101p2109).

We report on a girl with holoprosencephaly and a small, de novo interstitial deletion of most of band 2(p21). The similarity between the cytogenetic findings and CNS malformations in our patient and those recently reported by Münke et al. [Am J Med Genet 30:929-938, 1988] suggests a phenotypic relationship between deletion of this band and holoprosencephaly.

Neonatal progeroid syndrome: more than one disease?

We report on an infant with the neonatal progeroid syndrome whose clinical course and autopsy findings indicate that this may be a heterogeneous phenotype. The infant had intrauterine growth retardation, absence of subcutaneous fat, and a wizened, aged face, all apparently characteristic of the condition, but also had congenital heart defects and urinary reflux not reported in previous cases. An elevated maternal serum alpha fetoprotein was noted at 16 weeks of gestation and late-onset growth retardation appeared after 31 weeks. Autopsy findings showed normal cerebral myelination, in contrast to findings of sudanophilic leukodystrophy in the one patient with the syndrome previously examined at autopsy. These findings suggest that the neonatal progeroid syndrome may be a phenotype and have more than one cause.

Trisomy 18/trisomy 13 mosaicism in an adult with profound mental retardation and multiple malformations.

We report on an adult woman with profound mental retardation and multiple anomalies who consists of 3 cell lines: one with trisomy 18, one with trisomy 13, and a normal cell line. Her phenotype includes manifestations of both trisomy syndromes. The origin of these cell lines could have been a doubly aneuploid (48,XX + 13, + 18) or singly aneuploid (47,XX + 18 or 47,XX + 13) zygote with subsequent mitotic nondisjunctions, or a normal zygote with multiple mitotic nondisjunctions. There have been four previous reports of mosaicism involving both trisomy D and trisomy E; all died in the first six months of life. Two of these cases had a doubly aneuploid (48,XX, + D + E) cell line. Our patient illustrates the need for study of several tissues in patients with complex aneuploidy syndromes or atypical manifestations of a given syndrome (such as prolonged survival), as well as the need for caution in counseling families about prognosis for survival in autosomal trisomies which usually are lethal.

Deletion (13)(q14.1q14.3) in two generations: variability of ocular manifestations and definition of the phenotype.

A 5-yr-old girl with unilateral retinoblastoma was found to have del(13)(q14.1q14.3). Her 16-month-old sister and 35-year-old mother, with retinal colobomata but without retinoblastoma, have the same deletion. Esterase D studies indicate reduced gene dose at this locus in the 3 females, consistent with a deletion of band 13q14. These patients are of apparently normal intelligence but have a mildly "coarse" facial appearance, a broad nasal bridge, upturned nares, and a long upper lip with thin upper lip vermillion similar to the phenotype suggested by Motegi et al [1983a] for patients with this deletion. Review of the literature documents 2 other patients with deletions of band 13q14 but without retinoblastoma, indicating that retinoblastoma is not a necessary consequence of this deletion. Of the 12 reported patients with deletions limited to band 13q14, seven had normal intelligence and five were macrocephalic. Insufficient clinical information is provided to draw conclusions about phenotype. The family which we describe and those reviewed by Motegi et al suggest that there may be a characteristic appearance in patients with this deletion.

Information collected during the residency match process does not predict clinical performance.

OBJECTIVE: To determine whether information collected during the National Resident Matching Program (NRMP) predicts clinical performance during residency. METHODS: Ten faculty members rated the overall quality of 69 pediatric house officers as clinicians. After rating by the faculty, folders were reviewed for absolute rank on the NRMP match list; relative ranking (where they ranked in their postgraduate year 1 [PGY-1] group); scores on part I of the National Board of Medical Examiners (NBME) examination; grades during medical school pediatrics and internal medicine rotations; membership in the Alpha Omega Alpha Medical Honor Society; scores of faculty interviews during intern application; scores on the pediatric in-service examination during PGY-1; and scores on the American Board of Pediatrics certification examination. RESULTS: There was substantial agreement among faculty raters as to the overall quality of the residents (agreement rate, 0.60; kappa = 0.50; P = .001). There was little correlation between faculty ratings and absolute (r = 0.19; P = .11) or relative (r = 0.20; P = .09) ranking on the NRMP match list. Individuals ranked in the top 10 of the match list had higher faculty ratings than did their peers (mean +/- SD, 3.66+/-1.22 vs. 3.0+/-1.27; P = .03), as did individuals ranked highest in their PGY-1 group (mean +/- SD, 3.88+/-1.45 vs. 3.04+/-1.24; P = .03). There was no correlation between faculty ratings and scores on part I of the NBME examination (r = 0.10; P = .49) or scores on the American Board of Pediatrics certification examination (r = 0.22; P = . 11). There were weak correlations between faculty ratings and scores of faculty interviews during the intern application process (r = 0.27; P = .02) and scores on the pediatric in-service examination during PGY-1 (r = 0.28; P = .02). There was no difference in faculty ratings of residents who were elected to Alpha Omega Alpha during medical school (mean +/- SD, 3.32+/-1.21) as compared with those who were not (mean +/- SD, 3.08+/-1.34) (P = .25). CONCLUSIONS: There is significant agreement among faculty raters about the clinical competence of pediatric residents. Medical school grades, performance on standardized examinations, interviews during the intern application process, and match-list ranking are not predictors of clinical performance during residency.

Normal pyruvate oxidation in Friedreich ataxia and Charcot-Marie-Tooth disease fibroblasts.

Partial defects in activity of the pyruvate dehydrogenase complex have been described by some investigators in cell lines from Friedreich ataxia and Charcot-Marie-Tooth disease patients. Methylene blue was used to stimulate the rate of pyruvate oxidation in two different assay systems of pyruvate dehydrogenase activity in cultured human fibroblasts to determine if such partial defects, if present, could be detected in a stimulated assay system. Cell lines from normal controls, five patients with Friedreich ataxia, six related persons with Charcot-Marie-Tooth disease patients were studied. Although methylene blue (at a concentration of 25 mumol/l) significantly increased pyruvate oxidation in both assay systems and in all cell lines studied, no significant differences in pyruvate oxidation could be demonstrated between the control cells and either the Friedreich ataxia or Charcot-Marie-Tooth cell lines.