Homocystinuria is a rare autosomal recessive disorder of the transsulfuration or methylation pathway in methionine metabolism.
We present a case of a 25 years old female, who presented with rapid onset loss of vision in both eyes and short-sightedness. She had a background of well-controlled epilepsy, normal mental and physical development. She had no family history of Marfans syndrome.
On examination, systemic review was unremarkable and she was clinically euthyroid. She had high arched palate with no other stigmata of Marfans syndrome. Ocular examination revealed inferior nasal subluxation of her lens bilaterally with zonule dehiscence.
Routine haematology and biochemistry indices were normal. Vitamin B concentration was 152 ng/L (191-663 ng/L). Urine homocysteine concentration was 524.5 umol/L (2.0-14.2 umol/L), and plasma homocysteine concentration measured on two occasions was 237.9 umol/L and 254.5 umol/L (0-16.0 umol/L) respectively. Genetic test confirmed a heterozygous pathogenic mutation on the cystathionine B synthase (CBS) gene c.833T>C; p1278T. ECG and Echo were normal. CT angiogram revealed normal aortic root dimensions.
Low protein diet was recommended. She was commenced on Pyridoxine 100 mg TDS. Folic acid and Vitamin B12 were supplemented. She was treated with bilateral vitrectomy and lensectomy with right intra-ocular lens implant. Increased risk of thromboembolism was also discussed and managed appropriately.
Although visual disturbances have been described as a complication in more common metabolic problems such as Thyroid Eye Disease, it is worth remembering rare metabolic causes in patients presenting with visual problems. Prompt diagnosis and management of a homocystinuria can reduce the risk of thromboembolic stroke in the young (<30 years).