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Genetics Consultation

Consultation on Predictive Neurological Disease Testing for Late Installation

  • Predictive tests are genetic tests performed on asymptomatic individuals with a family history of late-onset neurological diseases, and are intended to predict the future risk of an inherited disease. These may be pre-symptomatic tests, susceptibility tests, and carrier tests. They identify the individuals at risk of a specific disease, in which we do not know its beginning, its evolution and its gravity.

  • They allow family members at risk to plan future children, justification for controlled clinical surveillance, including invasive techniques to reduce morbidity and mortality.

  • Because it is not a diagnostic test, conducting predictive tests requires one or more consultations of Medical Genetics and Neuropsychology.

Objectives:

  • Identifies individuals at risk for a specific disease

  • Report on a future disease that may or may not develop

  • Prevention of diseases

  • Family planning

  • Plan for medical or surgical follow-up

  • Not a diagnostic test

  • Effective but imperfect treatment

  • Gene analysis with high predictive value

Late-Onset Neurological Diseases, Examples

  • Alzheimer's disease

Alzheimer's disease (AD) is a dementia that begins slowly and progressively, associated with progressive loss of cortical neurons associated with the presence of beta-amyloid substance deposits. Dementia is a complex, mostly multifactorial disease with some well-known risk factors: age, family history of AD, and vascular risk factors (hypercholesterolemia, smoking, chronic ethanolism, diabetes mellitus, and hypertension uncontrolled arterial disease, chronic viral infections, etc.).

Prevalence has increased proportionately with life expectancy. It is the 1st most common neurodegenerative disease in the world.

It is estimated that about 25% of the etiology of AD is of family origin. The susceptibility to this disease is associated with the presence of APOE alleles. The genes identified from hereditary and early-onset AD are Presenilin 1 and 2 and have an autosomal dominant transmission.

  • Huntington's disease

Huntington's disease (DH) is a degenerative neurological disease, autosomal dominant, with a clinical picture characterized by involuntary choreotic movements, cognitive changes, and frequently associated with psychiatric pathology: depression and behavioral changes.

In its etiopathogenesis, DH has a protein that results from the expansion of triplets in the gene, located on chromosome 4p16.3, which is expressed in the central nervous system.

  • Machado-Joseph disease

Machado-Joseph disease, SCA3, is a progressive neurological disease characterized by progressive installation of ataxia (gait coordination problems) and involuntary eye movements.

It is an autosomal dominant disease, and originated in two families from the island of Flores. The mutation results from an expansion of triplets in the ataxin-3 gene, located on chromosome 14q24.3-q32.

  • Parkinson's disease

Parkinson's disease is characterized by a clinical picture constituted by tremor, muscular rigidity and slowing of movements. It is the 2nd most common neurodegenerative disease in the world. It affects 1% of adults over 55 years of age and 3% of adults over 75 years of age. It is considered a multifactorial disease that results from the interaction of several genes with environmental factors.

However, there are inherited forms of Parkinson's: Juvenile Parkinson's disease, the form of recessive transmission associated with the PARK2 gene and the dominant forms associated with PARK1, PARK3 and PARK8 genes.

  • Familial amyloid polyneuropathy

Familial amyloid polyneuropathy (PAF), also known as foot disease, is characterized by a neurological disease, progressive peripheral polyneuropathy, associated with nephropathy, cardiomyopathy and vitreous opacity. Usually, in most patients, it begins in the 3rd to 4th decade of life, and in a minority in the 6-7th-8th decades.

It is an autosomal dominant disease (transmitted from parents to offspring), caused by the presence of an amyloid substance, transthyretin, produced by a mutation in the TTR gene located on chromosome 18q11.2-q12.1.

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