PubMed Health⌕ Search

Biomedical subjects

C G Summers

Publications and source records attributed to C G Summers.

At least 19 recordsLinked to original sources
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↗
PubMed1991

Temperature-sensitive tyrosinase associated with peripheral pigmentation in oculocutaneous albinism.

Several types of autosomal recessive oculocutaneous albinism (OCA) are associated with abnormal tyrosinase function and a generalized reduction in or absence of cutaneous and eye melanin. Each is thought to result from a different mutant allele at the tyrosinase locus, with the mutation producing an enzyme with little or no activity in all involved tissues. In this paper, we report a new type of OCA that results from a tyrosinase allele producing a temperature-sensitive enzyme. The proband had white hair in the warmer areas (scalp and axilla) and progressively darker hair in the cooler areas (extremities) of her body. Melanocyte and melanosome architecture were normal. Quantitative hairbulb tyrosinase (dopa oxidase) assay demonstrated a loss of activity above 35-37 degrees C. Plasma pheomelanin and urine eumelanin intermediates were reduced and correlated with hair melanin content. This is the first temperature-sensitive tyrosinase mutation to be reported in humans and is analogous to the Siamese mutation in the cat and the Himalayan mutation in the mouse.

Albinism, Oculocutaneous↗
PubMed1991

Three different frameshift mutations of the tyrosinase gene in type IA oculocutaneous albinism.

Mutations in the gene for the pigment-producing enzyme tyrosinase are responsible for type IA (tyrosinase-negative) oculocutaneous albinism (OCA). Most reported mutations have been single base substitutions. We now report three different frameshift mutations in three unrelated individuals with type IA OCA. The first individual has a single base deletion within a series of five guanidines, resulting in a premature stop codon in exon I on one allele and a missense mutation at codon 382 in exon III on the homologous allele. The second individual is a genetic compound of two separate frameshift mutations, including both the same exon I single base deletion found in the first individual and a deletion of a thymidine-guanidine pair, within the sequence GTGTG, forming a termination codon (TAG) in exon I on the homologous allele. The third individual has a single base insertion in exon I on one allele and a missense mutation at codon 373 in exon III on the homologous allele. The two missense mutations occur within the copper Bbinding region and may interfere with either copper binding to the enzyme or oxygen binding to the copper. These five different mutations disrupt tyrosinase function and are associated with a total lack of melanin biosynthesis.

Albinism, Oculocutaneous↗
PubMed1990

Visual anomalies associated with albinism.

All mammals with hypopigmentation of the retinal pigment epithelium have abnormal visual systems. Albino mammals have been found to have: (1) reduced numbers of uncrossed optic fibers projecting to all visual centers, (2) disorganization of the pattern (lamination) of the dorsal lateral geniculate nuclei, and (3) disorganization of projections from the dorsal lateral geniculate nuclei to the visual cortex. The disorganization of central visual centers has catastrophic effects on stereovision and optokinetic nystagmus. Variable expression in oculocutaneous albinism suggests that affected individuals cannot always be identified by hypopigmentation, reduced visual acuity and nystagmus. Careful observation of foveal development in individuals even with normal vision is necessary to detect all persons with albinism. The scalp-recorded visually evoked potential designed to detect optic misrouting is the most reliable concomitant for determining albinism.

Albinism↗
PubMed1990

Albinism and Hermansky-Pudlak syndrome in Puerto Rico.

Five types of oculocutaneous albinism and two types of ocular albinism were found among 349 Puerto Rican albinos. The most prevalent type of albinism was the Hermansky-Pudlak syndrome (HPS). HPS was observed in five of every six albinos in Puerto Rico. The prevalence of HPS was highest in the northwestern quarter of the island, affecting approximately one in 1,800 persons, and approximately one in 22 are carriers of the gene. HPS is an autosomal recessively inherited triad of a tyrosinase-positive type of albinism, a hemorrhagic diathesis due to storage pool deficient platelets and accumulation of ceroid in tissues. The pigmentary phenotype of HPS albinos resembled that of any other type of oculocutaneous or ocular albinism. The most reliable method of diagnosing HPS is by a deficiency of platelet dense bodies observed by electron microscopy. The accumulation of ceroid in the tissues is associated with fibrotic restrictive lung disease and granulomatous enteropathic disease. The enteropathic disorder resembles Crohn's disease and with few exceptions, had its onset after 13 years of age. The major causes of death were fibrotic restrictive pulmonary disease, hemorrhagic episodes and sequelae of granulomatous enteropathic disease. Menometrorrhagia was common in women with HPS. No immune deficiency was found in HPS patients. The majority of patients with HPS had visual acuities of 20/200 or worse and consequently were legally blind. Albinos of all types, including HPS, lacked binocular vision due to nearly complete crossing of the optic tracts.

Albinism, Ocular↗
PubMed1989

Ocular changes in the mucopolysaccharidoses after bone marrow transplantation. A preliminary report.

Metabolic correction and physiologic response were evaluated after bone marrow transplantation in mucopolysaccharidosis. Eleven patients were prospectively evaluated to determine the effect of bone marrow transplantation on the progressive ocular manifestations of these disorders. Follow-up of 0.6 to 2.8 years after successful donor stem cell engraftment showed that some patients had slow clearing of the corneal clouding, reduction of intracytoplasmic inclusions in the conjunctiva, resolution of optic nerve edema, and stabilized or improved retinal function as determined by electroretinography. These preliminary results suggest that early bone marrow transplantation may alter some of the progressive ophthalmic characteristics of the mucopolysaccharidoses. Long-term follow-up is necessary to determine if these early alterations in the ocular features are predictive of a prolonged functional improvement in the visual status.

Bone Marrow Transplantation↗
PubMed1988

Hermansky-Pudlak syndrome. Ophthalmic findings.

Prospective ophthalmic evaluation was performed in 20 individuals with Hermansky-Pudlak syndrome, a type of oculocutaneous albinism with an associated deficiency of dense bodies in platelets. The extent of visual impairment and the possible relationship to the degree of hypopigmentation were studied. All patients showed nystagmus, visual acuity ranged from 20/60 to 20/400, and correction of refractive error provided a mild improvement in vision. Iris pigmentation varied in amount and did not correlate with the visual acuity measurement. Foveal hypoplasia was found in all patients, but variability in macular transparency and vascular architecture was noted. Visual-evoked potentials performed in 11 patients demonstrated excessive decussation of optic fibers. Recognition of this form of oculocutaneous albinism is important because of the associated pulmonary, gastrointestinal, renal, and cardiac manifestations of Hermansky-Pudlak syndrome.

Adolescent↗
PubMed1988

Clinical significance of hematic cyst of the orbit.

Hematic cyst is a rarely encountered orbital lesion consisting of encapsulated blood or blood breakdown products. The abnormality may be recognized by identifying the cystic structure by B-scan ultrasonography or computed tomography. Cysts located peripherally in the orbit tend to have histologic features suggesting hematoma formation. More centrally located orbital cysts are sometimes associated with vascular abnormalities. In other cases, the etiology is obscure, as in the case presented here. The visual prognosis is usually good, and associated systemic abnormalities are lacking.

Adult↗
PubMed1988

Paroxysmal facial itch: a presenting sign of childhood brainstem glioma.

Two children with neurofibromatosis and a chief complaint of severe, episodic, unilateral facial itching were found to have brainstem glioma. Initial computerized tomography of the brain was thought to be normal, but the brainstem tumor was subsequently demonstrated on magnetic resonance imaging. The paroxysmal facial itching resolved in both cases after a course of radiation therapy. The pathophysiology of the attacks of facial itching is unknown but must be related to the brainstem glioma. This is the first report of paroxysmal, unilateral facial itching as a presenting sign of childhood brainstem tumor.

Brain Neoplasms↗
PubMed1988

Albinism.

Genetic abnormalities of the melanin pigment system in which the synthesis of melanin is reduced or absent are called albinism. The reduction in melanin synthesis can involve the skin, hair follicle, and eye, resulting in oculocutaneous albinism, or can be localized primarily to the eye, resulting in ocular albinism. Approximately 1 in 17,000 individuals in the United States has oculocutaneous albinism, and more than 1 per cent of the population are heterozygous for a gene producing albinism.

Albinism↗
PubMed1987

Use of a modified binocular visual field to assess cyclodiplopia.

The patient who notes binocular diplopia may indicate that horizontal, vertical, or cyclorotary components are present. Although the single binocular visual field provides an indication of the area which is free of horizontal and vertical diplopia, it does not assess cyclorotary diplopia. A simple modification of the single binocular visual field which allows determination of the clinical significance of the cyclorotary component of diplopia is presented. Reproducible information is easily obtained, assisting in patient follow-up and management.

Adolescent↗
PubMed1987

Argon laser treatment of periocular lesions: an experimental study.

Argon laser photocoagulation is a promising alternative in the treatment of vascular lesions of the lid and periocular tissues. Experimental argon laser treatment of feline ocular and oral mucosa was undertaken to identify a protective shield that was satisfactory in preventing ocular damage and to identify a power that would be effective but avoid significant side effects.

Animals↗
PubMed1985

Juvenile iridoschisis and microphthalmos.

Spontaneous iridoschisis and corneal edema developed in the microphthalmic eye of an 8-year-old. There was no history of trauma, inflammation, or congenital iris abnormality.

Cell Count↗
PubMedDate not supplied

Vision despite tomographic absence of the occipital cortex.

A 14-month-old boy with developmental delay showed microcephaly, spastic diplegia, central visual fixation and an esotropia. A head tomographic scan disclosed absence of normal occipital cortex and electroencephalography showed markedly reduced voltages over the occipital region. Visual development in this patient may be related to heterotopic occipital cortex of a functioning non-striate system of visual processing. Visual function cannot be predicted when severe developmental anomalies of the occipital cortex are detected with computerized tomography.

Abnormalities, Multiple↗
PubMedDate not supplied

Ocular motor apraxia associated with intracranial lipoma.

Congenital ocular motor apraxia is rarely associated with brain tumors. A 10-month-old girl with normal vertical eye movements and head thrusting to initiate horizontal saccades is presented. CT brain scan revealed a midline posterior fossa mass and histopathology confirmed the clinical diagnosis of lipoma. Unlike previously described cases of posterior fossa brain tumors associated with congenital ocular motor apraxia, this patient showed persistent ocular motor apraxia despite complete resection of the tumor.

Apraxias↗