Introduction

Transcobalamin (TC) transports cobalamin (vitamin B₁₂) from plasma into cells. Its congenital deficiency is a rare autosomal recessive disorder due to mutations in the TCN2 gene. It causes intracellular cobalamin depletion with early onset in the first months of life, failure to thrive with pallor due to megaloblastic anemia. It can be associated with pancytopenia, gastrointestinal symptoms with vomiting, diarrhea, and neurological complications with myelopathy. Aggressive vitamin B12 parenteral therapy must be instituted early and continuously. Retinopathy and maculopathy are rarely associated with this condition.

Subject

We report the electrophysiological results of one TC-deficient patient diagnosed at the age of 4 months immediately and continuosly treated by hydroxocobalamin IM. Her visual function was followed by eight ophthalmological assessments, eight flash-ERG, six EOG, one mf-ERG, and seven P-ERG recordings over a 10-year period, between the age of 2y 9 m and 12y 6 m.

Results

Her ophthalmological assessment including visual acuity, fundi, optical coherent tomography (OCT), and retinal nerve fiber layer (RNFL) remained normal. From the age of 2y 9 m to 5y, dark-adapted and light-adapted flash-ERGs, EOGs and pattern-ERG were normal. From the age of 6y 4 m to 12y 6 m, dark-adapted flash-ERGs and EOGs remained normal. Cone a-wave amplitudes remained normal, whereas cone b-wave and flicker-response amplitudes were decreased. At the age of 12y 6 m, mf-ERG N1P1 amplitudes on the central 30° were decreased. From the age of 7y 4 m to 12y 6 m, P-ERG P50 amplitudes were decreased with no N95.

Comments

While clinical and anatomical assessments remained normal over a 10-year period, patient’s electrophysiological results suggested the progressive onset of a subclinical retinopathy of inner-cone dystrophy type, and a subclinical maculopathy on the central 30° including the ganglion cell layer deficiency on the central 15°, despite continuous intramuscular treatment, RPE and scotopic system remaining normal. The origins of such subclinical retinopathy and maculopathy are unknown and independent of early disease identification and aggressive intramuscular hydroxocobalamin therapy.

中文翻译：

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转钴胺素缺乏症的亚临床黄斑病变和视网膜病变：10 年随访

介绍

转钴胺素 (TC) 将钴胺素（维生素 B ₁₂）从血浆转运到细胞中。由于TCN2基因突变，其先天性缺陷是一种罕见的常染色体隐性遗传病。它会导致细胞内钴胺素耗尽，并在生命的最初几个月内早发，由于巨幼红细胞性贫血而无法茁壮成长。它可能与全血细胞减少、伴有呕吐、腹泻的胃肠道症状和伴有脊髓病的神经系统并发症有关。必须尽早并持续地进行积极的维生素 B12 肠外治疗。视网膜病变和黄斑病变很少与这种情况相关。

主题

我们报告了一名在 4 个月大时立即诊断并继续接受羟钴胺 IM 治疗的 TC 缺陷患者的电生理结果。在 10 年期间（2 岁 9 岁至 12 岁 6 岁之间）对她的视觉功能进行了 8 次眼科评估、8 次 flash-ERG、6 次 EOG、1 次 mf-ERG 和 7 次 P-ERG 记录。

结果

她的眼科评估包括视力、眼底、光学相干断层扫描 (OCT) 和视网膜神经纤维层 (RNFL) 保持正常。2y 9 m至5y，暗适应和光适应flash-ERGs、EOGs和pattern-ERGs正常。从 6 岁 4 m 到 12 岁 6 m，暗适应的 flash-ERG 和 EOG 保持正常。锥 a 波幅度保持正常，而锥 b 波和闪烁响应幅度降低。在 12y 6 m 时，中央 30° 的 mf-ERG N1P1 振幅降低。从 7 岁 4 米到 12 岁 6 米，P-ERG P50 振幅降低，没有 N95。

注释

虽然临床和解剖学评估在 10 年内保持正常，但患者的电生理结果表明内锥体营养不良型亚临床视网膜病变的进行性发作，以及中央 30° 的亚临床黄斑病变，包括中央的神经节细胞层缺陷15°，尽管持续肌内治疗，RPE 和暗视系统仍然正常。这种亚临床视网膜病变和黄斑病变的起源是未知的，并且与早期疾病识别和积极的肌内羟钴胺治疗无关。