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Genetics Neuro:

Red ragged muscle fibers are seen in mitochondrial diseases. Muscle fibers have this appearance because

abnormal mitochondria accumulate under the sarcolemma. Mitochondrial diseases show maternal

inheritance.

An increased number of trinucleotide repeats on the HD gene is associated with Huntington disease. The

larger the number of the repeats, the earlier the onset of the disease. Trinucleotide expansion occurs duringpaternal transmission, causing a genetic phenomenon called anticipation.

Neurofibromatosis type l is a single-gene autosomal-dominant disorder. It occurs due to mutation of the

NF-1 gene located on the chromosome i 7. Cafe-au-lait spots, multiple neurofibromas, and Lisch nodules

are the most common symptoms.

Early-onset (

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A -amyloid plays an important role in the development of Alzheimer disease. Its precursor protein (APP)

is coded by a gene located on chromosome 21. Patients with trisomy 21 (Down syndrome) are likely to

develop Alzheimer disease after age 40.

Other conditions associated with Down syndrome include:

1. Acute leukemias: both AML and ALL

2. Congenital heart disease: endocardial cusion defect, VSD, ASD

3. GIT defects: duodenal atresia and Hirschsprung disease