Tay-Sachs (TS) disease is a monogenic recessive disorder involving the lysosome’s lipid storage function. In this case, there is an accumulation of ganglioside GM2 in the brain cells. Deficiency in HEX-A leads to impaired biodegradation of the gangliosides. During infancy, there is normal development but an accumulation of the gangliosides with age leads to muscle atrophy and consequent paralysis. Some of the symptoms that present before this include loss of vision, problems in swallowing, deafness and seizures. Tay-Sachs disease does not have a treatment so far. Supportive treatment in form of seizure control using anticonvulsants and good nutrition are however helpful. The most effective way of avoiding TS is having a prenatal diagnosis (NINDS para 1-2).
Tay-Sachs disease results from hexosaminidase A (HEX-A) isoenzyme deficiency. There is rapid degeneration of neurons and the affected individual experiences slowed development. Due to the rapid and continuous degeneration, death mainly occurs at the age of 3 to 4 years. This is mainly due to recurring infections. The incidence of TS has been particularly high among the Ashkenazi Jews, where 1 in every 27 U.S. Jews carries the TS gene. This is in comparison to 1 in every 250 persons in other populations (Genome.gov para 7).
The autorecessive nature of TS implies that a child develops the disease only if each of the parents has the mutant gene (the couple must be heterozygous). This implies that there exists a 25% probability of developing the disease for every child born of carrier parents. The existence of only one of the two gene copies that produce HEX-A is enough to prevent Tay-Sachs from occurring. However, individuals with one inactive copy are carriers and will be phenotypically healthy (Genome.gov para 4-5).
I would enlighten the couple that Tay-Sachs disease is a condition that is inherited from carrier parents. The disease involves progressive neurodegeneration which is eventually fatal by the age of four years. During the disease, the couple should expect the child to experience vision loss, deafness and swallowing difficulties. The couple should also expect psychological anomalies such as seizures in the child. The above events are expected to progress rapidly to muscle wasting, paralysis and eventual death. In a bid to help the couple understand why their child has TS yet none of them has the disease, I would explain to the couple that the disease affects the child if both parents are carriers of the defective gene. This means that both parents may present normal but they are able to pass down the gene to their offspring. In this case, there is a 25% likelihood of passing the gene to their children. At the same time, there is a 50% likelihood of having their offspring as carriers of the condition.
The lack of any history of TS in the families of the couple is an indication that each parent obtained the defective gene from parents who were carriers of a single copy of the defective gene; with the other copy being normal hence they all appear healthy. The most appropriate advice for this couple would be to undergo prenatal diagnosis for TS in any subsequent pregnancy. This would be effective in preventing further passing down of the disease to their offspring. I would propose molecular prenatal diagnostic procedures such as pre-implantation genetic diagnosis as among the most effective preventive measures.
Works Cited
Genome.gov. Learning about Tay-Sachs disease. National Human Genome Research Institute, 2011. Web.
NINDS. NINDS Tay-Sachs disease information page. National Institute of Neurological Disorders and Stroke, 2007. Web.