China
Africa
Explore chapters and articles related to this topic
Disorders of Pigmentation
Published in Ayşe Serap Karadağ, Lawrence Charles Parish, Jordan V. Wang, Roxburgh's Common Skin Diseases, 2022
Michael Joseph Lavery, Charles Cathcart, Hasan Aksoy
Overview: Oculocutaneous albinism is the most common form of albinism, which is inherited in an autosomal recessive pattern. The lack of pigment is the result of deficiency in tyrosinase, which renders the individual unable to synthesize melanin despite maintaining the same number of basal melanocytes.
Chediak−Higashi Syndrome
Published in Dongyou Liu, Handbook of Tumor Syndromes, 2020
Children with classic CHS tend to display: (i) partial oculocutaneous albinism (OCA, pigment dilution in hair, skin, and eyes, results in silvery or metallic hair [observable under the light microscope], reduced skin, iris, and retinal pigmentation, photophobia, and nystagmus); (ii) immunodeficiency (frequent/severe infections of the skin, upper respiratory tract, and periodontal region); (iii) immunodeficiency (recurrent infections); (iv) bleeding tendency (epistaxis, gum/mucosal bleeding, and easy bruising); (v) HLH (or accelerated phase; manifesting as fever, hepatosplenomegaly, lymphadenopathy, neutropenia, anemia, and sometimes thrombocytopenia, in addition to diffuse lymphohistiocytic infiltration of the liver, spleen, bone marrow, lymph nodes, and central nervous system; possibly triggered by Epstein−Barr virus infection and absence of NK cell function); (vi) neurologic features (low cognitive abilities, balance abnormalities, stroke, coma, ataxia, tremor, absent deep-tendon reflexes, and motor and sensory neuropathies) (Figure 65.1) [1,13–22].
The skin
Published in Angus Clarke, Alex Murray, Julian Sampson, Harper's Practical Genetic Counselling, 2019
Generalised oculocutaneous albinism is autosomal recessive. Two main types exist: A severe form, OCA1A (with an absence of tyrosinase activity). Those with this form have a total lack of pigment throughout life and have two inactivating mutations in the tyrosinase gene (TYR).A milder tyrosinase-positive form, OCA2, for which the gene is also known (OCA2, corresponding to ‘pink eye’ in the mouse). Some milder cases of TYR mutations (with reduced tyrosinase activity) have a similar phenotype but the disorder is known as OCA1B.
Clinical albinism score, presence of nystagmus and optic nerves defects are correlated with visual outcome in patients with oculocutaneous albinism
Published in Ophthalmic Genetics, 2021
Alina V. Dumitrescu, Johnny Tran, Wanda Pfeifer, Sajag V. Bhattarai, Andrew Kemerley, Taylor V. Dunn, Kai Wang, Tod E. Scheetz, Arlene Drack
Oculocutaneous albinism (OCA) represents a heterogeneous group of disorders that affect melanin production. Melanin is required for pigmentation of the skin and hair as well as for proper development of the visual system, and defects in the pathway required for melanin synthesis can lead to OCA(1). The disorder has been referred to as ocular albinism (OA) when decreased pigmentation appears to be restricted to the eye; however, this is a misnomer since patients with “ocular albinism” have abnormal macro-melanosomes on skin biopsy (2,3). Besides, mutations in a recently discovered albinism-like gene, SLC38A8, result in normal skin pigmentation with ocular findings of albinism (4,5). In some syndromic forms of albinism, like Hermansky-Pudlak syndrome (HPS), melanosome biogenesis is primarily affected as well as maturation and secretion of lysosome-related organelles (6). Albinism often causes lifelong visual impairment, although the range of visual acuities is wide from legal blindness to only a minimal decrease in vision. The prevalence is estimated to be around 1/20,000 worldwide and affects people of all races and ethnicities (7). It is more common in parts of Africa, such as Zimbabwe, where the prevalence is estimated to be 1:4000 (8).
The challenges faced by clinicians diagnosing and treating infantile nystagmus Part I: diagnosis
Published in Expert Review of Ophthalmology, 2021
Eleni Papageorgiou, Irene Gottlob
Albinism has been traditionally divided into oculocutaneous albinism (OCA) or ocular albinism (OA) on the basis of phenotypical features. However, the recent advances in molecular genetics have expanded the classification of various albinism subtypes based on the genetic profile of patients. Oculocutaneous albinism (OCA) is characterized by disruption of melanin biosynthesis, resulting in a lack of pigmentation in the eyes, skin, and hair [80]. Oculocutaneous albinism is a group of autosomal recessive disorders which are classified into seven types according to the affected gene [81]. OCA1 is caused by mutations in the tyrosinase gene (TYR) and is present in most populations except African-Americans [81]. It can present with either a complete lack of melanin production (OCA1A) or partial melanin production (OCA1B). Mutations in OCA2, TYRP1, SLC45A2, SLC24A5, and LRMDA have been attributed to subtypes OCA2, OCA3, OCA4, OCA6, and OCA7, respectively [81]. OCA2 and OCA3 are more common in African populations and are milder forms of albinism. OCA4 is another mild form of albinism that has been recently found in Turkish, Japanese, German, and Korean patients [81]. For OCA6 and OCA7 there are only case reports in a Chinese family and a consanguineous Faroese family. OCA5 is very rare, and has been only mentioned in a case report of a Pakistani family. The OCA5 locus is at 4q24, but the causative gene has not yet been identified [82].
Nystagmus associated with macular dysplasia
Published in Strabismus, 2020
Patients with oculocutaneous albinism mainly showed macular dysplasia, abnormal foveal depression, and increased foveal thickness with persistence of an inner nuclear layer, an inner plexiform layer, a ganglion cell layer, and a nerve fiber layer on SD-OCT. It was revealed that fundus was lack of pigment in retinal pigment epithelium with visible large choroidal vessels (Figure 1). Congenital aniridia showed a planar fovea in the macula with the lack of a foveal pit with nystagmus (Figure 2). The OCT section showed the absence of normal foveal pit in foveal hypoplasia (Figure 3). For monocular macular heterotopias, no nystagmus was detected with naked eyes (Figure 4). Nystagmus was not found in patients with congenital macular coloboma and congenital retinoschisis. SD-OCT images showed a macular coloboma in the right eye and macular epiretinal membrane was seen in the left eye and no other abnormalities were observed (Figure 5). SD-OCT images showed the congenital retinoschisis in both eyes (Figure 6).