Retrospective: Study the developmental course of the spectrum of patients with hexosaminidase deficiency, infantile Tay-Sachs disease, from retrospective data to establish a historical control specifically for a gene therapy trial. To create a quantitative and qualitative natural history of infantile Tay-Sachs disease.

Prospective: Will characterize the developmental course of infants with Tay-Sachs disease and longitudinally examine individual growth trajectories.

The infantile form (Classic Infantile) is the most common. Infants with Tay-Sachs disease appear normal at birth but begin to manifest progressive weakness, loss of muscle strength such as sitting up or turning over, deafness, and decreased attentiveness at approximately 6-10 months. This is followed by rapid deterioration of motor and slowed mental development (neurodegeneration), often with seizures. Retinal involvement leads to visual impairment and eventual blindness. Death typically occurs by the age of five.Currently there is no treatment for Tay-Sachs disease.

This study will focus on the developmental course of the spectrum of patients with hexosaminidase deficiency, infantile Tay-Sachs disease, from retrospective data to establish a historical control specifically for a gene therapy trial. The data from this study will be necessary to provide end-points for future therapies, guide medical decisions about treatment, provide objective measurement of treatment outcomes, and accurately inform parents regarding potential outcomes.

1. Retrospective data will be collected and analyzed to establish an historical control specifically for a gene therapy trial and generally for other treatments in children with infantile Tay-Sachs. It is important for all individuals identified with Hexosaminidase A deficiency to participate in the study in order to collect data for subsequent natural history studies for both juvenile and late onset forms; however, the current study will analyze infantile Tay-Sachs records as this is the population that will be selected for the gene therapy study.
2. Prospective: As new patients are seen at the University of Minnesota data will be collected to characterize the developmental course in infants with Tay-Sachs disease and longitudinally examine individual growth trajectories and with larger numbers be able to model the effects of predictors using developmental growth curve analysis. New patients will complete neurodevelopmental evaluations, clinical and laboratory observations, and possibly psychophysiological (event related potentials) measures. Data will be quantified to develop a stage of disease and disease severity scale.

Inclusion Criteria:

• individuals identified with Hexosaminidase A deficiency

Exclusion Criteria:

• individuals not identified with Hexosaminidase A deficiency