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Biomedical subjects

D Creel

Publications and source records attributed to D Creel.

At least 19 recordsLinked to original sources
PubMed1996

Children and adolescents with neurofibromatosis 1: a behavioral phenotype.

Twenty 6- to 17-year-old children with neurofibromatosis 1. (NF1) were compared to 20 age- and sex-matched siblings on a wide range of neuropsychological and behavioral dimensions. In familial cases, diagnostic status was confirmed by gene linkage with greater than 98% accuracy. Visual examinations that included assessments of visual evoked responses (VER) were performed on subjects with NF1. Forty-two percent of NF1 subjects had abnormal VER and underwent magnetic resonance imagery or computed tomography scans of the brain. On a variety of skills, subjects with NF1 performed more poorly than unaffected siblings. Children with NF1 were found to be less competent on measures of cognitive, language, and motor development, visual-spatial judgment, visual-motor integration, and academic achievement. Learning disabilities were common in children with NF1. Parents and teachers reported that NF1 subjects had internalizing problems and difficulty interacting with peers. A behavioral phenotype for NF1 and recommendations for preventative interventions are proposed.

Adolescent↗
PubMed1991

Variable expression of vision in sibs with albinism.

Oculocutaneous albinism is defined by the presence of cutaneous and ocular hypopigmentation, the latter associated with nystagmus, iris transillumination, reduced retinal pigment, foveal hypoplasia, and misrouting of the optic fibers at the chiasm. The visual acuity is variable but almost always reduced. We report on two brothers with oculocutaneous albinism and markedly different visual acuity. One brother has a visual acuity of 20/100, while the second has similar cutaneous pigmentation and visual acuity of 20/20 and had not previously been recognized as having oculocutaneous albinism. Both brothers have foveal hypoplasia and misrouting of the optic fibers at the chiasm. Biochemical analysis suggests that this is a tyrosinase-related type of oculocutaneous albinism. This study demonstrates that careful observation of foveal development in relatives with normal vision is necessary to detect all individuals with albinism in a family. A suspected diagnosis of albinism may be confirmed when the visual-evoked potentials show excessive decussation of the optic fibers at the chiasm.

Adolescent↗
PubMed1988

Electroretinograms in autism: a pilot study of b-wave amplitudes.

The authors recorded electroretinograms for 27 autistic patients and 20 age- and sex-matched healthy volunteers. Thirteen (48%) of the autistic patients demonstrated subnormal b-wave amplitudes, which may indicate abnormal retinal function. One patient was tested serially at two sites; his low b-wave amplitude did not vary over time or between the two sites. If this retinal finding can be confirmed at other laboratories and in larger samples of autistic patients, it might provide a marker for a specific subtype of autism.

Adolescent↗
PubMed1984

Dominant optic atrophy, deafness, ptosis, ophthalmoplegia, dystaxia, and myopathy. A new syndrome.

Twenty-three members of a 96-member family exhibited an autosomal dominant disorder which has not previously been described. This disorder involves progressive optic atrophy, abnormal electroretinography without retinal pigment changes, and progressive sensorineural hearing loss usually evident in the first or second decade of life. In midlife, ptosis, ophthalmoplegia, dystaxia, and a nonspecific myopathy occur.

Adult↗
PubMed1983

Auditory brainstem anomalies in albino cats. I. Evoked potential studies.

The amount of melanin pigmentation in the inner ear is positively correlated with the general pigmentation of the body and specifically with the amount of pigment in the eye. The misrouting of retinofugal projections which accompanies ocular and oculocutaneous albinism has been thought to be a defect in decussation unique to the visual system. Evidence suggests that functional abnormalities may also exist in the auditory systems of albino humans and animals. To evaluate this possibility, evoked potential techniques were used to examine the functional anatomy of decussating brainstem auditory pathways in albino and pigmented cats. Auditory brainstem responses (ABRs) were recorded from albino, pigmented, and Siamese cats using monaural stimulation. ABRs were recorded ipsilateral and contralateral to the stimulated ear. The albinos were complete tyrosinase-negative (cc), not the dominant white (W) variety associated with deafness. In pigmented cats, the amplitudes of ABRs recorded with the reference electrode ipsilateral to the stimulated ear and the ABRs recorded using the reference contralateral to the stimulated ear did not differ by more than 40% for individual components appearing between 2 and 4 ms after stimulus onset. In albino cats the components at these latencies were obliterated or greatly attenuated in the ABR recorded using the reference contralateral to the stimulated ear. These data indicate that anomalies may exist in the brainstem at the level of the acoustic striae, superior olivary nuclei and/or trapezoid body in tyrosinase-negative albino cats.

Animals↗
PubMed1983

Visual and auditory anomalies in Chediak-Higashi syndrome.

Albinism is correlated with misrouting of decussating retinal fibers in the brain. There is also evidence of anomalies of decussating auditory pathways in albinos. The Chediak-Higashi syndrome (CHS) is a rare form of partial albinism which includes increased susceptibility to infections, a hemorrhagic tendency and peripheral polyneuropathies. Binocular and monocular pattern-onset visually evoked potentials (VEPs) and monaural auditory brain stem responses (ABRs) were recorded from 4 subjects with CHS. Three of the CHS demonstrated asymmetric monocular VEPs and failed the Titmus stereovision test. All 4 CHS produced asymmetric ABRs similar to those reported for albinos. Although the hair, skin and irises are relatively well pigmented in CHS, these individuals apparently have anomalies of their central visual and auditory pathways.

Auditory Pathways↗
PubMed1983

Sudden severe visual loss associated with peripapillary burns during panretinal argon photocoagulation.

A 31-year-old woman lost central visual acuity in her left eye during scatter argon laser photocoagulation when her ophthalmologist treated the temporal peripapillary region. There was no evidence for a vascular explanation. Previous experimental work showed that the lateral spread of thermal energy into the optic nerve parenchyma from the peripapillary pigment epithelium and choroid can destroy adjacent nerve fibres. There is a risk of thermal optic neuropathy caused by peripapillary photocoagulation.

Adult↗
PubMed1982

Pattern evoked potentials in phenylketonuria.

Humans with untreated phenylketonuria (PKU) are candidates for having misrouted optic projections related to their hypopigmentation. Six tractable PKUs were tested using scalp-recorded evoked potentials. Both pattern reversal and pattern onset/offset (appearance/disappearance) stimuli were used under conditions of binocular and monocular stimulation. Evoked potentials were of normal form and hemispheric symmetry following both monocular and binocular stimulation in 5 of the 6 PKUs. The exception demonstrated a small hemispheric asymmetry upon stimulation of the left eye, but not following stimulation of the right eye. The asymmetry observed in this subject was probably idiosyncratic and not representative of PKUs in general. Four of the 6 PKUs produced reversal. This may be related to incomplete postnatal myelination. There appears to be no detectable optic misrouting in PKU. In spite of total absence of fetal phenylalanine hydroxylase activity, availability of tyrosine and melanin pigment is evidently sufficient during early development of the visual system to permit normal decussation of optic fibers at the chiasm.

Adult↗
PubMed1982

Retinal projections in tyrosinase-negative albino cats.

Retinal projections were examined in two tyrosinase-negative albino cats using autoradiographic techniques. Cats from this colony have pink eyes; their retinal pigment epithelium, ciliary body, and iris epithelium are completely devoid of melanin pigment. Test breeding for five generations indicates that these cats are true albinos (cc). The most striking feature of the albino cats' visual pathways was a reduction in ipsilateral input which was more severe than that reported for Siamese cats. The only evidence of ipsilateral input to the laminated dorsal lateral geniculate nucleus of the albino was a small lateral normal segment and a small projection to the lateral portion of lamina C1. Ipsilateral projections to the medial interlaminar nucleus, retinal recipient zone of the pulvinar complex, ventral lateral geniculate nucleus, superior colliculus, and pretectum also were reduced. Ipsilateral projections to the suprachiasmatic nucleus appeared to be normal in the albino cats studied. Our findings indicate that, compared to the normal cat as well as to the tyrosine-positive Siamese cat, the tyrosinase-negative albino has reduced ipsilateral retinal projections. The albino cat is a model system analogous to tyrosinase-negative albinism found in mammals.

Albinism↗
PubMed1982

Abnormal retinal projections in cats with the Chediak-Higashi syndrome.

The Chediak-Higashi syndrome (CHS) occurs in mammals, including humans and cats. The CHS is characterized by decreased oculocutaneous pigmentation, enlarged cytoplasmic granules, increased susceptibility to infections, and a hemorrhagic tendency. Ocular anomalies include pale irides and albinotic or subalbinotic fundi. Cats with CHS also have photophobia and prolonged postrotatory nystagmus. Since hypopigmentation of the pigment epithelium is correlated with misrouting of retinal ganglion cells in mammals, visual projections of CHS cats were examined by autoradiographic techniques to determine whether they exhibit abnormal retinogeniculate projections. In CHS cats, misrouted optic projections fragment layer A1 of the dorsal lateral geniculate nucleus into several islands, similar to the disruption of this lamina reported in the Siamese cat.

Animals↗
PubMed1981

Evoked potentials in albinos: efficacy of pattern stimuli in detecting misrouted optic fibers.

Misrouting of retinogeniculostriate projections associated with retinal hypopigmentation has been found to be a general phenomenon in mammals, including humans. Anomalous optic pathway projections of albinos may be detected by recording visually evoked potentials (VEPs). To determine the efficacy of various stimulus conditions for detecting misrouted optic fibers, we compared flash, modulated light, pattern reversal and pattern onset/offset (appearance/disappearance) stimuli. Pattern onset/offset were found superior in detecting anomalies of misrouting of retinogeniculostriate projections. As a group, humans with retinal hypopigmentation have poor evoked potentials to offset and pattern reversal stimuli. Nystagmus seems to be most symptomatic of poor pattern reversal responses. In general onset/offset pattern stimuli are more versatile for detection of abnormalities in the visual system than pattern reversal stimuli.

Adolescent↗
PubMed1980

Auditory brainstem anomalies in human albinos.

Brainstem auditory evoked potentials recorded from human albinos indicate significant hemispheric asymmetry. The asymmetry is symptomatic of differences between decussated and nondecussated auditory pathways in albino and pigmented humans at approximately the level of the superior olivary nuclei. Abnormal decussation of auditory pathways in albinos probably coincides with known visual system anomalies.

Adult↗
PubMed1980

Inappropriate use of albino animals as models in research.

Sensory-neural, biochemical-metabolic, and physiological anomalies occur in albino mammals. There are ontogenic and biochemical parallels between the senses, peripheral nervous system, endocrine glands, metabolism, and melanin pigmentation. All albino mammals examined have abnormal optic systems. Many drugs cannot be adequately evaluated in an albino model because of melanin's ability to bind and interact with some chemicals. There is evidence that a general reduction in melanin pigment is correlated with a paucity of amino acids necessary for normal chemical function of the brain. There is a high probability that enzyme levels indicative of metabolic performance are deficient in the liver and kidneys oif albinos. Congenital defects are associated with hypopigmentation in animal models and human syndromes. Melanin is found in abundance in the eye, inner ear, and midbrain where neural impulses are initiated indicating a possible role as an electrophysiologic mechanism. Microwave irradiation differentially affects albino and pigmented animals. Implications of these observations and other reports of anomalies associated with hypopigmentation suggest caution in the use of albino and other hypomelanotic animals as normal models in biological research.

Albinism↗
PubMed1980

Albinism in Nigeria with delineation of new recessive oculocutaneous type.

Seventy-nine Nigerian oculocutaneous albinos were investigated. Fifty-six had typical tyrosinase-positive albinism (TPA) and 23 had brown albinism (BA), a new oculocutaneous type. The TPA were characterized by localized but no generalized skin pigment, yellow hair, blue to brown irides, nystagmus, and reduced or absent retinal pigment. Localized skin pigment included freckles and lentigines. The iris and skin pigment were the result of the slow accumulation of pigment with age as both were found in older individuals. The most severe skin changes were premalignant keratoses and squamous cell carcinoma of the skin, and the skin malignancies were the major factor in limiting the lifespan for TPA. The BA were characterized by generalized light brown skin pigment, light brown hair, blue to brown irides, nystagmus, and reduced retinal pigment. There was little accumulation or change of pigment in the eyes or skin with age. The generalized light skin pigment was effective in reducing sensitivity to solar radiation and very few BA had premalignant keratoses. Pedigree analysis for BA suggested on autosomal recessive inheritance pattern.

Adolescent↗
PubMed1979

Ontogeny of the visual evoked response in the stump-tailed macaque.

Visual evoked responses (VER's) of stump-tailed macaques were studied from birth to 80 weeks in an attempt to establish the utility of this species as a model of human neurophysiological development. Although human subjects and monkeys share a unique complexity of the VER at birth, the postnatal development of their VER's does not appear to follow a parallel sequence. The relatively dynamic nature of the VER during the 1st few weeks in a monkey's life may limit the usefulness of this species as a model of human development. The rapid changes in the VER of the developing monkey and the observation that these changes continue beyond 2 years of age should be considered in studies of the VER in which repeated measures are obtained over a prolonged period of time.

Animals↗