Aim Neuronal ceroid lipofuscinosis type 2 (CLN2) disease is an autosomal recessive inherited neurodegenerative lysosomal storage disorder caused by deficient tripeptidyl peptidase 1 (TPP1) enzyme, leading to progressive deterioration of neurological functions commonly occurring in children aged 2–4 years and culminating in early death. Atypical cases associated with earlier or later symptom onset, or even protracted course, have already been reported. Such variable manifestations may constitute an additional challenge to early diagnosis and initiation of appropriate treatment. The present work aimed to analyse clinical data from a cohort of Latin American CLN2 patients with atypical phenotypes. Methods Experts in inborn errors of metabolism from Latin America selected patients from their centres who were deemed by the clinicians to have atypical forms of CLN2, according to the current literature on this topic and their practical experience. Clinical and genetic data from the medical records were retrospectively revised. All cases were presented and analysed by these experts at an Advisory Board Meeting in São Paulo, Brazil, in October 2018. Results Seizures, language abnormalities and behavioural disorders were found as the first manifestations, appearing at the median age of 6 years, an older age than classically described for the late infantile form. Three novel mutations were also identified. Conclusion Our findings reinforce the inclusion of CLN2 in the differential diagnosis of children presenting with seizures, behavioural disorders and language abnormalities. Early diagnosis will allow early initiation of specific therapy.

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Introduction: Late infantile neuronal ceroid lipofuscinosis type 2 (CLN2), is a neurodegenerative autosomal recessive disease caused by TPP1 gene variants, with a spectrum of classic and atypical phenotypes. The aim of treatment is to slow functional decline as early as possible, improving quality of life and survival. This study describes the clinical characteristics as well as response to treatment with cerliponase alfa. Materials and Methods: A retrospective study was conducted in five Latin-American countries, based on clinical records from patients with CLN2. Clinical follow-up and treatment variables are described. A descriptive and bivariate statistical analysis was performed. Results: A total of 36 patients are reported with a mean age of symptom onset and time to first specialized consultation of 4.7±2.3 and 6±3.1 years, respectively. Seizures were the predominant symptom (80.6%). In a subgroup analysis, most patients with the classic phenotype exhibited regression in language (90%), while the patients with the atypical phenotype had seizures as the predominant symptom (87%). The mean age of symptom onset and time to first specialized consultation was 3.5±2.0 and 4.9±3.2 years, respectively, in patients with the classic phenotype and 6.2±1.8 and 7.5±2.4 in patients with the atypical phenotype. The mean time interval between onset of symptoms and treatment initiation was 3.8 years in patients with classic phenotype and 7.4 in patients with atypical phenotype. All patients were treated with cerliponase alfa, maintaining overall functional stability as compared to pretreatment values. Discussion and conclusion: This study reports at this time the largest number of patients with CLN2 in treatment with cerliponase alfa in the world. Data show a higher frequency of patients with atypical phenotype and a high allelic proportion of intron variants in our region. There was evidence of long intervals until first specialized consultation, diagnosis, and enzyme replacement therapy. Follow-up after the initiation of cerliponase alfa showed slower-to-no-progression of the disease, associated with adequate clinical outcomes and stable functional scores. These improvements were consistent in both clinical phenotypes.

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