q1 - aimhigh

[ArchivalUser]

The parents of a 6-month-old child who was normal at birth bring her into the clinic. Since their emigration
to the
U.S. from Eastern Europe soon after her birth, the child has developed diminished responsiveness,
progressive
blindness and deafness, and recently, seizures. Serum levels of which of the following compounds
would be
expected to be decreased in both of the parents?
A. Dystrophin
B. Hexosaminidase A
C. Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
D. Phenylalanine hydroxylase
E. Vitamin D3

[ArchivalUser]

dd??

[ArchivalUser]

bb tay sachs d

[ArchivalUser]

sorry change to bb

[ArchivalUser]

bb

[ArchivalUser]

The correct answer is B. This patient has Tay-Sachs disease, an autosomal recessive disorder caused
by the
deficiency of hexosaminidase A, which leads to the accumulation of ganglioside GM2 in neurons,
producing a
degenerative neurologic disease. Children appear normal at birth, but then begin to suffer from
diminished
responsiveness, deafness, blindness, loss of neurologic function, and seizures. A cherry-red spot on the
macula
may be seen by ophthalmoscopic examination. Death usually occurs by 4 to 5 years of age. There is
no therapy.
The incidence is higher among Jews of Eastern European descent. Since the parents must be
heterozygotes for
the mutant hexosaminidase A allele, they would be expected to have diminished levels of the enzyme.