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A previously healthy 13 year-old boy presented with acute-onset headaches, aphasia and right-sided hemiparesis. Imaging showed cerebral ischemic infarction due to bilateral carotid occlusion, and investigation for stroke etiology diagnosed homocystinuria. Homocystinuria is an autosomal recessive condition that affects the metabolism of the amino acid methionine due to an enzyme deficiency. This disorder involves multiple organs systems, and complications include thromboembolic events, ectopia lentis, mental retardation, and skeletal abnormalities. The early diagnosis and treatment of hyperhomocystinemia can significantly improve outcomes. Therefore, metabolic screening for homocystinuria is strongly recommended for children presenting with stroke.

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ABSTRACT Homocystinuria is a treatable autosomal recessive inherited disorder. This condition may cause life-threatening complications such as thromboembolic events. Coronavirus disease 2019 (COVID-19) is associated with an increased risk of venous thromboembolic events. Here, we report a case of late diagnosis of homocystinuria presenting with deep venous thrombosis and COVID-19. This study highlights a sustained high index of suspicion for homocystinuria to prevent severe thromboembolic complications.

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PURPOSE: Deficiency in Cystathionine ß-synthase (CBS) leads to an abnormal accumulation of homocysteine and results in classical homocystinuria, a multi-systemic disorder that affects connective tissue, muscles, the central nervous system, and the eyes. However, the genetic players and mechanisms underlying vision alterations in patients with homocystinuria are little understood. MATERIALS AND METHODS: The fruit fly, Drosophila melanogaster, is a useful system to investigate the genetic basis of several human diseases, but no study to date has used Drosophila as model of homocystinuria. Here, we use Drosophila genetic tools to down-regulate CBS expression and evaluate its behavioral response to light. RESULTS: We show that CBS-deficient flies do not display the normal stereotypical behavior of attraction towards a luminous source, known as phototaxis. This behavior cannot be attributed to a motor or olfactory deficiency, but it is most likely related to a lower visual acuity. CBS-deficient flies are overall smaller, but smaller eyes do not explain their lack of phototactic response. CONCLUSIONS: The vision phenotype of CBS knock-down flies is consistent with severe myopia in homocystinuria patients. We propose to use Drosophila as a model to investigate ocular manifestations underlying homocystinuria.

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BACKGROUND: Classic homocystinuria (HCU), or cystathionine beta-synthase (CBS) deficiency, is a rare inborn error of methionine metabolism. Main clinical features may include skeletal and vascular manifestations, developmental delay, intellectual disability and eye disorders. MATERIAL AND METHODS: This is an observational and retrospective study aiming at describing eye abnormalities presented by a cohort of late-diagnosed HCU patients. Data regarding ophthalmological evaluation included visual acuity, refraction, biomicroscopy, Perkins tonometry, fundus examination, retinography, biometry, ocular ultrasound, optical coherence tomography, anterior segment photography and topography. RESULTS: Ten patients with HCU (20 eyes) were included. The most frequent findings were ectopia lentis(n = 20) and myopia (n = 9). Biometry, ultrasound, OCT and topography findings were available for four patients. One patient had keratoconus; one had abnormal retinal pigmentation; and two had lens surgery scars with irregular astigmatism. CONCLUSIONS: Eye abnormalities are very frequent in late-diagnosed HCU patients. The presence of ectopia lentis should always raise the diagnostic hypothesis of HCU.

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OBJECTIVE: describe cardiovascular findings from echocardiograms and electrocardiograms in patients with Classic Homocystinuria. METHODS: this retrospective exploratory study evaluated fourteen subjects with Classic Homocystinuria (median age = 27.3 years; male n = 8, B6-non-responsive n = 9 patients), recruited by convenience sampling from patients seen Hospital de Clínicas de Porto Alegre (Brazil), between January 1997 and July 2020. Data on clinical findings, echocardiogram and electrocardiogram were retrieved from medical records. RESULTS: Eight patients presented some abnormalities on echocardiogram (n = 6) or electrocardiogram (n = 5). The most frequent finding was mild tricuspid regurgitation (n = 3), followed by mitral valve prolapse, mild mitral regurgitation, enlarged left atrium and aortic valve sclerosis (n = 2 patients each). Aortic root ectasia was found in one patient. Venous thrombosis was reported in six patients: deep vein thrombosis of lower limbs (n = 3), ischaemic stroke (n = 1), cerebral venous sinus thrombosis (n = 1) and pulmonary vein thrombosis (n = 1). CONCLUSION: mild valvulopathies seen to be common in patients with Classic Homocystinuria, but more studies regarding echocardiogram and electrocardiogram in this population are needed to draw absolute conclusions.

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BACKGROUND: Biallelic pathogenic variants in CBS gene cause the most common form of homocystinuria, the classical homocystinuria (HCU). The worldwide prevalence of HCU is estimated to be 0.82:100,000 [95% CI, 0.39-1.73:100,000] according to clinical records and 1.09:100,000 [95% CI, 0.34-3.55:100,000] by neonatal screening. In this study, we aimed to estimate the minimal worldwide incidence of HCU. METHODS: The 25 most common pathogenic alleles of HCU were identified through a literature review. The incidence of HCU was estimated based on the frequency of these common pathogenic alleles in a large genomic database (gnomAD). RESULTS: The minimum worldwide incidence of HCU was estimated to be ~0.38:100,000, and the incidence was higher in Europeans non-Finnish (~0.72:100,000) and Latin Americans (~0.45:100,000) and lower in Africans (~0.20:100,000) and Asians (~0.02:100,000). CONCLUSION: Our data are in accordance with the only published metanalysis on this topic. To our surprise, the observed incidence of HCU in Europeans was much lower than those described in articles exploring small populations from northern Europe but was similar to the incidence described on the basis of neonatal screening programs. In our opinion, this large dataset analyzed and its population coverage gave us greater precision in the estimation of incidence.

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Classical homocystinuria (HCU) is characterized by increased plasma levels of total homocysteine (tHcy) and methionine (Met). Treatment may involve supplementation of B vitamins and essential amino acids, as well as restricted Met intake. Dysbiosis has been described in some inborn errors of metabolism, but has not been investigated in HCU. The aim of this study was to investigate the gut microbiota of HCU patients on treatment. Six unrelated HCU patients (males = 5, median age = 25.5 years) and six age-and-sex-matched healthy controls (males = 5, median age = 24.5 years) had their fecal microbiota characterized through partial 16S rRNA gene sequencing. Fecal pH, a 3-day dietary record, medical history, and current medications were recorded for both groups. All patients were nonresponsive to pyridoxine and were on a Met-restricted diet and presented with high tHcy. Oral supplementation of folate (n = 6) and pyridoxine (n = 5), oral intake of betaine (n = 4), and IM vitamin B12 supplementation (n = 4), were reported only in the HCU group. Patients had decreased daily intake of fat, cholesterol, vitamin D, and selenium compared to controls (p < 0.05). There was no difference in alpha and beta diversity between the groups. HCU patients had overrepresentation of the Eubacterium coprostanoligenes group and underrepresentation of the Alistipes, Family XIII UCG-001, and Parabacteroidetes genera. HCU patients and controls had similar gut microbiota diversity, despite differential abundance of some bacterial genera. Diet, betaine, vitamin B supplementation, and host genetics may contribute to these differences in microbial ecology.

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Resumen: En este artículo se presenta el caso de una niña de 13 años con historia de cefalea de 2 años de evolución, la cual ha sido estudiada por subluxación del cristalino y fenotipo marfonoide. Para llevar a cabo la investigación se realizó una tomografía cerebral simple que evidenció trombosis de varios senos cerebrales. Posteriormente se hospitalizó a la paciente en la unidad de cuidados intensivos, mientras se anticoagulaba con enoxaparina. Se solicitó un estudio para trombofilia junto con homocisteina en sangre, ante la sospecha de homocistinuria. Luego de confirmarse el diagnóstico se recetó piridoxina y ácido fólico, con lo cual la paciente evolucionó de manera satisfactoria y recuperó las funciones perdidas. El seguimiento de este caso para la investigación permitió encontrar una disminución mayor del 20 % de la homocisteina, sin que sus niveles estuvieran por debajo de 50 µmol/L, hecho que hace a la paciente respondedora parcial a la piridoxina.

Abstract: This article presents the case of a 13-year-old girl with a 2-year history of headache, which has been studied for lens subluxation and Marfanoid phenotype. To carry out this research, a simple brain tomography was performed that showed thrombosis of several sinuses. Subsequently, the patient was hospitalized in the intensive care unit and anticoagulated with enoxaparin. A study was requested for thrombophilia along with homocysteine in blood, on suspicion of homocystinuria. After confirming the diagnosis, pyridoxin and folic acid were prescribed, with which the patient evolved satisfactorily and recovered lost functions. Follow-up on this case for the research allowed us to find a decrease in homocysteine greater than 20 %, without its levels being below 50 µmol/L, which makes the patient partially responsive to pyridoxine.

Resumo: Neste artigo, é apresentado o caso de uma menina de 13 anos, com história de cefaleia de dois anos de evolução, a qual tem sido estudada por subluxação do cristalino e fenótipo marfanoide. Para realizar a pesquisa, foi tomada uma tomografia cerebral simples que evidenciou trombose de vários seios cerebrais. Em seguida, a paciente foi internada na unidade de tratamento intensivo onde recebeu tratamento anticoagulante com enoxaparina. Foi solicitado um estudo para trombofilia junto com homocisteina em sangue, diante da suspeita de homocistinúria. Após o diagnóstico ter sido confirmado, foram receitados piridoxina e ácido fólico, com os quais o estado da paciente evoluiu de maneira satisfatória e ela recuperou as funções perdidas. O seguimento do caso para a pesquisa permitiu verificar uma diminuição maior de 20% da homocisteina, sem que seus niveis estivessem abaixo de 50 µmol/L, fato que torna a paciente apta parcialmente à piridoxina.

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Abstract Genetic homocystinurias are a group of inborn errors of metabolism that result in the massive excretion of homocysteine (Hcy) in the urine due to Hcy accumulation in the body, usually causing neurological and cardiovascular complications. The three most frequent causes are classical homocystinuria [deficiency of cystathionine beta-synthase (CBS)], methylmalonic aciduria with homocystinuria, cblC type (cblC deficiency) and severe methylenetetrahydrofolate reductase (MTHFR) deficiency. In this review, we highlight the similarities and differences among these disorders. Briefly, their joint manifestation is the accumulation of tHcy, however, the other sulfur amino acids show various and even invers profiles. Vascular disease, developmental delay and seizures are found in all homocystinurias, nevertheless, the complications of CNS differ in a wide variety of presentations and severities and are apparently less pronounced in CBS deficiency. Moreover, patients with remethylation defects typically do not present ectopia lentis and bone disturbances, tall stature and osteoporosis. Whereas hematological alterations, such as megaloblastic anemia, thrombocytopenia neutropenia and life-threatening microangiopathy, are specific findings of cblC deficiency.

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ABSTRACT Homocystinuria is one of a group of genetic disorders called inborn errors of metabolism. It is characterized by a deficiency of the enzyme that converts homocysteine to cystathionine. Keratoconus is an ophthalmologic condition characterized by thinning of the corneal stroma, which causes the cornea to assume a conical shape. There is little information in the scientific literature about the association between keratoconus and homocystinuria. We believe that a collagen cross-linking defect may be the key to understand the connection between these two conditions. This case report describes a 38-year-old male patient with a diagnosis of classical homocystinuria since age 13. At the age of 16, he received a diagnosis of asymmetrical keratoconus when referred for lensectomy with vitrectomy of his left eye. To the best of our knowledge, this is the first report of a patient with simultaneous homocystinuria and keratoconus.

RESUMO Homocistinúria é parte de um grupo de doenças genéticas chamado erros inatos do metabolismo. É caracterizada por uma deficiência da enzima que converte a homocisteína em cistationina. O ceratocone é uma patologia oftalmológica caracterizada pelo afinamento do estroma corneano, o que faz com que a córnea assuma um formato cônico. Há pouca informação na literatura científica sobre a associação entre ceratocone e homocistinúria. Acreditamos que um defeito no cross-linking do colágeno possa ser a chave para entender a conexão entre estas duas condições. Este relato de caso descreve um paciente masculino de 38 anos com diagnóstico de homocistinúria clássica desde os 13 anos. Aos 16 anos, recebeu o diagnóstico de ceratocone assimétrico quando foi encaminhado para lensectomia com vitrectomia do olho esquerdo. Até onde sabemos, este é o primeiro relato de um paciente com homocistinúria e ceratocone simultâneos.

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BACKGROUND: Classical homocystinuria (HCU) is a monogenic disease caused by the deficient activity of cystathionine ß-synthase (CßS). The objective of this study was to identify the CBS mutations in Brazilian patients with HCU. METHODS: gDNA samples were obtained for 35 patients (30 families) with biochemically confirmed diagnosis of HCU. All exons and exon-intron boundaries of CBS gene were sequenced. Gene expression analysis by qRT-PCR was performed in six patients. Novel missense point mutations were expressed in E. coli by site-directed mutagenesis. RESULTS: Parental consanguinity was reported in 16 families, and pyridoxine responsiveness in five (15%) patients. Among individuals from the same family, all presented the same phenotype. Both pathogenic mutations were identified in 29/30 patients. Twenty-one different mutations were detected in nine exons and three introns; being six common mutations. Most prevalent were p.Ile278Thr (18.2%), p.Trp323Ter (11.3%), p.Thr191Met (11.3%), and c.828+1G>A (11.3%). Eight novel mutations were found [c.2T>C, c.209+1delG, c.284T>C, c.329A>T, c.444delG, c.864_868delGAG c.989_991delAGG, and c.1223+5G>T]. Enzyme activity in E. coli-expressed mutations was 1.5% for c.329A>T and 17.5% for c.284T>C. qRT-PCR analysis revealed reduced gene expression in all evaluated genotypes: [c.209+1delG; c.572C>T]; [c.2T>C; c.828+1G>A]; [c.828+1G>A; c.1126G>A]; [c.833T>C; c.989_991delAGG]; [c.1058C>T; c.146C>T]; and [c.444delG; c.444delG]. The expected phenotype according to the genotype (pyridoxine responsiveness) matched in all cases. CONCLUSIONS: Most patients studied were pyridoxine nonresponsive and presented early manifestations, suggesting severe phenotypes. Many private mutations were observed, but the four most prevalent mutations together accounted for over 50% of mutated alleles. A good genotype-phenotype relationship was observed within families and for the four most common mutations.

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Abstract This study described a broad clinical characterization of classical homocystinuria (HCU) in Brazil. This was a cross-sectional, observational study including clinical and biochemical data from 72 patients (60 families) from Brazil (South, n = 13; Southeast, n = 37; Northeast, n = 8; North, n = 1; and Midwest, n = 1). Parental consanguinity was reported in 42% of families. Ocular manifestations were the earliest detected symptom (53% of cases), the main reason for diagnostic suspicion (63% of cases), and the most prevalent manifestation at diagnosis (67% of cases). Pyridoxine responsiveness was observed in 14% of patients. Only 22% of nonresponsive patients on treatment had total homocysteine levels <100 mmol/L. Most commonly used treatment strategies were pyridoxine (93% of patients), folic acid (90%), betaine (74%), vitamin B12 (27%), and low-methionine diet + metabolic formula (17%). Most patients diagnosed with HCU in Brazil are late diagnosed, express a severe phenotype, and poor metabolic control. Milder forms of HCU are likely underrepresented due to underdiagnosis.

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BACKGROUND: We describe body composition, lipid metabolism and Stearoyl-CoA desaturase-1 (SCD-1) indices in patients with classical homocystinuria (HCU). METHODS: Eleven treated HCU patients and 16 healthy controls were included. Body composition and bone mineral density were assessed by dual X-ray absorptiometry. Sulfur amino acids (SAA) and their derivatives (total homocysteine, cysteine, methionine, S-adenosylmethionine, S-adenosylhomocysteine, and glutathione), lipids (free fatty acids, acylcarnitines, triglycerides and lipoproteins), glucose, insulin, leptin, adiponectin, and isoprostanes were measured in plasma. Insulin resistance was evaluated by HOMA-IR. To estimate liver SCD-1 activity, SCD-16 [16:1(n-7)/16:0] and SCD-18 [18:1(n-9)/18:0] desaturation indices were determined. RESULTS: In HCU patients, SCD-16 index was significantly reduced (p=0.03). A trend of an association of SCD-16 index with cysteine was observed (r=0.624, p=0.054). HCU patients displayed lower lean mass (p<0.05), with no differences in fat mass percentage. Leptin and low-density lipoprotein concentrations were lower in HCU patients (p<0.05). Femur bone mineral density Z-scores were correlated with plasma cysteine (r=0.829; p=0.04) and total homocysteine (r=-0.829; p=0.04) in HCU patients. CONCLUSIONS: We report alterations in leptin and SCD-1 in HCU patients. These results agree with previous findings from epidemiologic and animal studies, and support a role for SAA on lipid homeostasis.

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ABSTRACT Purpose: Artisan iris-claw lens implantation (AICLI) is a surgical technique for treating ectopia lentis. We aimed to compare visual outcomes and possible long-term complications of AICLI surgery in pediatric patients with ectopia lentis with or without a diagnosable hereditary disease. Methods: Seventeen children with non-traumatic ectopia lentis were retros pectively classified into two groups: group 1 included children with a diagnosable hereditary disease (11 patients, 65%), and group 2 included children without any definable hereditary disease (six patients, 35%). Patients were evaluated for post-surgical refraction, best-corrected visual acuity, and clinical follow-up complications. Results: The average follow-up time was 38 months, and the average age of the patients was 103 ± 53 months (30-196 months). Best-corrected visual acuity values were significantly increased in both groups after surgery (p<0.05). Target refraction values were achieved at a rate of 47% in group 1 and 22% in group 2. Post-surgery complications, such as lens dislocation (36%, 11 eyes of 10 patients) and hypotonia (10%, three eyes of three patients) were observed in both groups, and retinal detachments (10%, three eyes of three patients) were observed in three patients from group 1. Conclusions: Compared with previous similar studies, this study utilized the largest pediatric patient group and had the longest post-surgery follow-up time. Moreover, it is advisable that pediatric patients with non-traumatic ectopia lentis be carefully screened for any underlying hereditary disease, especially diseases related to connective tissue metabolism.

RESUMO Objetivo: A implantação de lentes intraoculares de fixação iriana em garra (AICLI) é uma técnica cirúrgica para o tratamento de ectopia lentis. Nosso objetivo foi comparar resultados visuais e possíveis complicações em longo prazo da cirurgia de AICLI em pacientes pediátricos com ectopia lentis com ou sem doença hereditária diagnosticável. Métodos: Dezessete crianças com ectopia lentis não-traumática foram classificadas retrospectivamente em dois grupos: o grupo 1 com pacientes apresentando doença hereditária diagnosticável (11 pacientes, 65%) e o grupo 2 com pacientes sem qualquer doença hereditária definível (6 pacientes, 35%). Os pacientes foram avaliados quanto à sua refração pós-operatória, acuidade visual melhor corrigida e complicações. Resultados: O tempo médio de seguimento foi 38 meses. A média de idade dos pacientes foi de 103 ± 53 meses (30-196 meses). Os valores de acuidade visual me lhor corrigida aumentaram significativamente em ambos os grupos (p<0,05). Os valores de refração alvo foram alcançados a uma taxa de 47% no grupo 1 e 22% no grupo 2. Complicações pós-operatórias como luxação da lente (36%, 11 olhos de 10 pacientes) e hipotonia (10%, 3 olhos de 3 pacientes) foram observados nos dois grupos e foram observados descolamentos de retina (10%, 3 olhos de 3 pacientes) em 3 pacientes do grupo 1. Conclusões: Em comparação com relatos anteriores na literatura, este estudo utilizou um grupo maior de pacientes pediátricos e tempo de seguimento pós-operatório mais longo. É aconselhável que pacientes pediátricos com ectopia lentis não-traumática sejam cuidadosamente selecionados em relação a doença subjacente hereditária, especialmente as doenças relacionadas com o metabolismo do tecido conjuntivo.

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Homocystinuria is an inborn error of amino acid metabolism caused by deficiency of cystathionine ß-synthase (CBS) activity, biochemically characterized by homocysteine (Hcy) and methionine (Met) accumulation in biological fluids and high urinary excretion of homocystine. Clinical manifestations include thinning and lengthening of long bones, osteoporosis, dislocation of the ocular lens, thromboembolism, and mental retardation. Although the pathophysiology of this disease is poorly known, the present review summarizes the available experimental findings obtained from patients and animal models indicating that oxidative stress may contribute to the pathogenesis of homocystinuria. In this scenario, several studies have shown that enzymatic and non-enzymatic antioxidant defenses are decreased in individuals affected by this disease. Furthermore, markers of lipid, protein, and DNA oxidative damage have been reported to be increased in blood, brain, liver, and skeletal muscle in animal models studied and in homocystinuric patients, probably as a result of increased free radical generation. On the other hand, in vitro and in vivo studies have shown that Hcy induces reactive species formation in brain, so that this major accumulating metabolite may underlie the oxidative damage observed in the animal model and human condition. Taken together, it may be presumed that the disruption of redox homeostasis may contribute to the tissue damage found in homocystinuria. Therefore, it is proposed that the use of appropriate antioxidants may represent a novel adjuvant therapy for patients affected by this disease.

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An association between sulfur amino acids (methionine, cysteine, homocysteine and taurine) and lipid metabolism has been described in several experimental and population-based studies. Changes in the metabolism of these amino acids influence serum lipoprotein concentrations, although the underlying mechanisms are still poorly understood. However, recent evidence has suggested that the enzyme stearoyl-CoA desaturase-1 (SCD-1) may be the link between these two metabolic pathways. SCD-1 is a key enzyme for the synthesis of monounsaturated fatty acids. Its main substrates C16:0 and C18:0 and products palmitoleic acid (C16:1) and oleic acid (C18:1) are the most abundant fatty acids in triglycerides, cholesterol esters and membrane phospholipids. A significant suppression of SCD-1 has been observed in several animal models with disrupted sulfur amino acid metabolism, and the activity of SCD-1 is also associated with the levels of these amino acids in humans. This enzyme also appears to be involved in the etiology of metabolic syndromes because its suppression results in decreased fat deposits (regardless of food intake), improved insulin sensitivity and higher basal energy expenditure. Interestingly, this anti-obesogenic phenotype has also been described in humans and animals with sulfur amino acid disorders, which is consistent with the hypothesis that SCD-1 activity is influenced by these amino acids, in particularly cysteine, which is a strong and independent predictor of SCD-1 activity and fat storage. In this narrative review, we discuss the evidence linking sulfur amino acids, SCD-1 and lipid metabolism.

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OBJETIVO: Avaliar os resultados pós-operatórios da subluxação congênita do cristalino, corrigida por uma nova abordagem cirúrgica. MÉTODOS: Foram estudados 21 olhos de 13 pacientes, portadores de subluxação não traumática do cristalino submetidos à cirurgia na Fundação Altino Ventura, no período de abril de 1999 a abril de 2004. A idade média foi de 8,7 ± 5,4 anos, e o tempo médio de seguimento foi 21,5 ± 19,3 meses. Os pacientes foram submetidos à facoaspiração, implante do anel endocapsular e lente intraocular (LIO). Uma das alças da LIO foi amputada e apoiada sobre o anel, no interior do saco capsular, centralizando a LIO. RESULTADOS: Houve melhora da acuidade visual (AV) em todos os casos, e redução significante do equivalente esférico e componente esférico comparando-se a refração pré e pós-operatória (p<0,01). Não houve diferença entre o componente cilíndrico pré e pós-operatório (p=0,71). Opacificação da cápsula posterior do cristalino foi a complicação encontrada em 71,4 por cento dos casos. Foi realizada capsulotomia posterior precoce nestes pacientes sem intercorrências. CONCLUSÃO: Implante de LIO com uma alça amputada e apoiada sobre o anel endocapsular é uma opção no tratamento cirúrgico da subluxação congênita do cristalino, podendo-se observar centralização da LIO e melhora da AV no pós-operatório.

PURPOSE: To evaluate the postoperative results of congenital lens subluxation corrected by a new technique. METHODS: Retrospective chart review of 21 eyes of 13 patients with no traumatic lens subluxation who underwent surgery in Altino Ventura Foundation from April, 1999 to April, 2004. The mean age was 8.7 ± 5.4 years old, and the mean follow-up period was 21.5 ± 19.3 months. Patients underwent phacoaspiration, endocapsular ring and intraocular lens (IOL) implantation. The implanted IOL had one loop haptic excised and was supported above the ring, inside the capsular bag promoting intraocular lens centralization. RESULTS: Visual acuity improvement was observed in all cases. There was a significant reduction of the spherical equivalent and spherical component comparing the pre and postoperative refraction (p<0.01). There was no statistically significant difference between the pre and postoperative cylinder component (p=0.71). Posterior capsule opacification was a postoperative complication found in 71.4 percent of the cases. Early posterior capsulotomy was performed with no complications in these cases. CONCLUSION: Intraocular lens implantation with one loop haptic amputed and supported above the endocapsular ring is an option for the congenital lens subluxation surgical treatment, promoting lens centralization and postoperative visual acuity improvement.

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Introducción. Homocistinuria es la segunda causa de aminoacidopatías, después de fenilcetonuria. Se hereda en forma autosómica recesiva. El defecto está en el cromosoma 21 q 22.3. Incidencia: 1:300 000 a 1:60 000. Es un trastorno del metabolismo de la metionina con aumento de homocisteína, y alteraciones en ojos y sistemas nervioso central, cardiovascular y esquelético. Casos clínicos. Mujeres de 9 y 11 años, con retardo psicomotor, pérdida de la agudeza visual y actividad motora, subluxación de cristalino, nistagmo, mala oclusión dentaria, prognatismo, escápulas aladas, aracno y clindactilia, genuvalgo, pie cavo, ataxia y signo de Romberg positivo. Tamiz metabólico: caso 1: metionina 1 194 (normal 7-47 ng/mL), B12 1 167 (normal 220-960 pg/mL), folatos 20-7.2 (normal 3-17 ng/ mL). Caso 2: metionina 180-1 740, vitamina B12: 1 749 y 1 744, folatos 3. Tratamiento: piridoxina, folatos, vitamina C, B12 y aspirina. Evolución estable. Conclusión. El diagnóstico oportuno de homocistinuria previene complicaciones.

Introduction. Homocystinuria is a metabolic disorder of methionine which results elevated homocysteine, visual, central nervous system, cardiovascular system and skeletal disturbances, and the second most frequent amino acid disorder after phenylcetonuria. It is a recessive autosomic hereditary condition. The defect is located in chromosome 21q22-3. Incidence: 1:300 000 to 1:60 000. Case reports. Two girls ages 9 and 11 years presented with mental retardation, loss of visual acuity and of motor activity; lens sub luxation, nistagmus, ataxia and positive Romberg's sign. Metabolic screening: Case 1: methionine, 1 194 ng/mL (normal, 7-47 ng/mL); B12, 1 167 pg/mL (normal, 120-960 pg/mL); folates, 20-7.2 ng/mL (normal, 3-17 ng/mL). Case 2: methionine, 180-1 740; vitamin B12, 1 749; folates 3 (normal 3-17 ng/mL). Treatement: pyridoxine, folates, vitamin C, B12 and aspirin. The clinical course of these patients has been stable. Conclusion. Early diagnosis of homocystinuria prevents complications.