Tay Sachs Disease

Original Editor - Mmesoma Eyisi

Top Contributors - Mmesoma Eyisi and Khloud Shreif  

Introduction

Tay-Sachs disease (TSD) is a rare autosomal recessively inherited progressive neurodegenerative disorder. It is caused by a deficiency of the enzyme hexosaminidase A, which results in the accumulation of GM2 gangliosides within nerve cells, leading to mortality in early childhood. This buildup triggers nerve cell degeneration, impairing nervous system function and leaving the patient with severely reduced mental and physical capacity. Other names for TSD include GM2 gangliosidosis and hexosaminidase A deficiency.

Epidemiology

The incidence of TSD is extremely low, occurring in approximately 1 in 320,000 live births in the United States. However, the carrier frequency is significantly higher, affecting roughly 1 in 250 individuals who possess the mutated gene. TSD is more prevalent among the people of Ashkenazi Jewish heritage.

The prevalence of Tay-Sachs disease carriers within the Jewish population in the United States is estimated to be approximately 3.45% (1 in 29), with an incidence of affected live births occurring at a rate of roughly 0.029% (1 in 3,500).

Classifications

TSD is classified into three based on the age of presentation: Infantile, Late juvenile, and Late-onset TSD. Infantile TSD is the most common type with late-onset TSD being the least common type.

Infantile Tay Sachs Disease

Infantile TSD typically appears in infants between 3-6 months old, starting with slowed growth, muscle weakness, and loss of motor skills such as rolling, sitting, and crawling. As the condition progresses, infants may experience seizures, dysphagia, myoclonic jerks, and vision loss. They also exhibit an exaggerated startle response to loud noises. This genetic disorder is caused by a deficiency of enzymes called hydrolases, which are essential for cellular function and are typically found in lysosomes. Over time, the lack of these enzymes leads to cellular damage and the progressive deterioration of physical and cognitive abilities.

Late Juvenile Tay Sachs Disease

Late Juvenile TSD, a neurodegenerative disorder, presents in early childhood ages 2-10 due to partial deficiency of hexosaminidase A (Hex A). The disease's progression correlates inversely with the age of onset.

Late Onset Tay-Sachs disease

Adult late-onset TSD is rare, often diagnosed late around 8+ years. It's less severe due to partial Hex A enzyme activity (5-20% normal). Symptoms start in adolescence/early adulthood (15-30 years). Psychiatric features are also very common in adult-onset Tay-Sachs disease. About 40% of individuals develop psychiatric manifestations without dementia, including recurrent psychotic depression, hebephrenic schizophrenia with disorganization of thoughts, delusion and hallucination, paranoia, and bipolar symptoms.

Clinical Presentation

The clinical presentation of TSD is unique with the symptoms varying with severity and age of onset. Typically, individuals with TSD appear asymptomatic at birth and develop normally during the first few months of life.

Initial Presentation 0-6 months

• Mild motor weakness
• ⁠Irritability
• ⁠Hypersensitivity to sensory stimuli
• ⁠Exaggerated startle response
• Cherry-red spot in the retina by fundoscopic examination

Progressive Symptoms 6-18 months

• ⁠⁠Vision reduction
• ⁠Blindness (by 30 months)
• ⁠Retinal vessel narrowing
• ⁠Nystagmus
• ⁠Optic atrophy
• ⁠Doll-like facies
• ⁠Hypotonia
• ⁠Delayed developmental milestone
• ⁠Seizures (tonic-myoclonic type)

Advanced Stage (1-2 years):

• Spasticity
• ⁠Myoclonic seizures
• ⁠Ataxia
• ⁠Dyskinesia
• ⁠Sleep disturbances
• ⁠Macrocephaly (due to reactive cerebral gliosis)
• ⁠Decerebrate posturing
• ⁠Dysphagia
• Psychotic Depression

Differential Diagnosis

Misdiagnosing TAD is common and misdiagnosis follows the presentations, when the lower motor neuron symptoms are predominant it is often misdiagnosed as

• Spinal muscular atrophies, such as the Kugelberg-Welander type or Progressive Muscular Atrophy.

When the upper motor neuron findings are prominent, patients may be misdiagnosed with

• Multiple sclerosis or Hereditary Spastic Paraplegia.

When cerebellar symptoms predominate, patients are often misdiagnosed with

• Spinocerebellar Ataxia

Other differentials

• Spinal muscular atrophy
• Friedreich ataxia
• Amyotrophic lateral sclerosis
• Kufs' disease
• Sandhoff disease

Management

There’s no cure for  TSD. Treatment is mainly supportive and aimed at adequate nutrition, controlling seizures, managing infectious disease, protecting the airway, and early aggressive physiotherapy and occupational therapy. Treatment focuses on symptom control and ensuring greater patient well-being.

In managing TSD, physiotherapy interventions are fundamental in addressing physical impairments, promoting functional abilities, and enhancing the overall quality of life for affected individuals. Individuals with TSD are managed to meet unique needs and symptom profiles.

Physiotherapy for Infantile TSD

• Chest Physiotherapy to prevent mucus buildup
• Therapeutic positioning to improve circulation
• Early mobilisation
• Range of motion exercises

Physiotherapy for Late Onset TSD

• Gait training to improve gait and prevent the risk of fall.
• Muscle strenghtening
• Joint mobilisation to help keep the joint flexible
• Balance training