Federico Justin R., Krishnamurthy Karthik
Baptist Medical Center
HCA Florida Orange Park Hospital
Albinism, from the Latin , meaning "white," is a group of heritable conditions associated with decreased or absent melanin in ectoderm-derived tissues (most notably the skin, hair, and eyes), yielding a characteristic pallor. The most commonly thought of presentation is that of oculocutaneous albinism (OCA). OCA is a group of phenotypically similar genetic disorders derived from errors in melanin synthesis. As the name implies, the most dramatic effects are in the eyes and skin. The skin manifestations are more heterogeneous and appear along with a spectrum of severity depending upon the subtype of OCA. The ocular structures rely upon melanin for signaling as they develop, in utero; thus, misrouted optic nerve fibers yield more uniform ocular manifestations of the disorder. To date, seven types of nonsyndromic albinism (OCA1 to OCA7) have been described. These are all due to isolated genetic mutations whose constellation of signs and symptoms do not manifest so broadly that they can be classified as syndromic. A discussion on albinism, however, would be incomplete without the mention of isolated ocular albinism (OA1) and the syndromic albinisms: Hermansky-Pudlak syndrome (HPS) and Chediak-Higashi syndrome (CHS). The syndromic albinisms have the same hallmark lack of dermal and ocular pigment as OCA. They, however, involve genes that encode for proteins that have more extensive applications to cellular function. Loss-of-function mutations in these genes, therefore, yield predictable systemic consequences associated with the syndromes mentioned. Examples include inactivation of genes involved in lysosomal synthesis (and not simply melanin synthesis) that lead to bleeding diathesis in HPS and propinquity to infection in CHS. Other conditions may present like albinism with congenital nystagmus and/or generalized hypopigmentation. Most of these are included in the Differential Diagnosis section. Of special mention is a pair of syndromes that derive their albino-like features because of deletions in the same genes that are mutated in OCA type 2: Angelman (AS) and Prader-Willi (PWS) syndromes.
白化病，源于拉丁语，意为“白色”，是一组遗传性疾病，与外胚层来源组织（最显著的是皮肤、毛发和眼睛）中黑色素减少或缺乏有关，导致特征性的苍白。最常被想到的表现形式是眼皮肤白化病（OCA）。OCA是一组表型相似的遗传性疾病，由黑色素合成错误引起。顾名思义，最显著的影响在眼睛和皮肤。皮肤表现更为多样，且根据OCA的亚型不同，严重程度也有所不同。眼部结构在子宫内发育时依赖黑色素进行信号传导；因此，视神经纤维走错路线会导致该疾病更一致的眼部表现。迄今为止，已描述了七种非综合征性白化病（OCA1至OCA7）。这些都是由孤立的基因突变引起的，其体征和症状的组合并不广泛到可被归类为综合征性。然而，关于白化病的讨论如果不提及孤立性眼部白化病（OA1）以及综合征性白化病：赫尔曼斯基-普德拉克综合征（HPS）和切迪阿克-希加综合征（CHS），就是不完整的。综合征性白化病与OCA一样，具有皮肤和眼部色素缺乏的相同特征。然而，它们涉及编码对细胞功能有更广泛应用的蛋白质的基因。因此，这些基因的功能丧失突变会产生与上述综合征相关的可预测的全身后果。例如，参与溶酶体合成（而不仅仅是黑色素合成）的基因失活会导致HPS中的出血倾向和CHS中易感染。其他疾病可能表现为类似白化病，伴有先天性眼球震颤和/或全身性色素减退。其中大多数包含在鉴别诊断部分。特别值得一提的是一对综合征，它们由于与OCA2型中突变的相同基因缺失而具有类似白化病的特征：安吉尔曼（AS）综合征和普拉德-威利（PWS）综合征。
