The phenomenon where subsequent generations are at the risk of earlier and more severe disease is known as:
Ans. d. Anticipation (Ref: Robbins We p168-171)The phenomenon where subsequent generations are at the risk of earlier and more severe disease is known as anticipation."Anticipation. This refers to the observation that clinical features of fragile X syndrome worsen with each successive generation, as if the mutation becomes increasingly deleterious as it is transmitted from a man to his grand- sons and great-grandsons. "--Robbins 9/e p169AnticipationAnticipation: A phenomenon whereby the symptoms of a genetic disorder become apparent at an earlier age as it is passed onto the next generation. In most cases, an increase of severity of symptoms is also noted.Anticipation is common in trinucleotide repeat disorders, such as Huntington's disease and myotonic dystrophy,where a dynamic mutation in DNA occurs.All of these diseases have neurological symptoms.The clinical features worsen with each successive generation, as if the mutation becomes increasingly deleterious as it is transmitted from a man to his grandsons and great-grandsons.Diseases showing anticipationAutosomal dominantAutosomal RecessiveX-linkedWithout Expression Type* Several spinocerebellar ataxiasQ* Huntington's disease: CAGQ* Myotonic dystrophy: CTGQ* Dyskeratosis congenitaQ* Freidreich's ataxia: GAAQ* (Freidreich's ataxia does not usually exhibit anticipation because it is an autosomal recessive disorder.)* Fragile X syndrome: CGGQ* Crohn's disease* Behcet's disease
Mosaicism
Imprinting
Pleiotropy
Anticipation
Nature of Gene Abnormalities