GENETICS: 1. Early onset of Mr. Jimenez\'s daughter is a phenomenon known as? 2.
ID: 90198 • Letter: G
Question
GENETICS:
1. Early onset of Mr. Jimenez's daughter is a phenomenon known as?
2. How many types of Myotonic dystrophy have been described, and how we can differentiate them?
3. What is the molecular basis for Myotonic dystrophy?
CLINICAL GENETICS PROBLEMS MOLECULAR GENETICS CASE 1 Mr Jimenez a 44-year-old male was recently diagnosed with Myotonic dystrophy and wants to know more about the disease. He reports that the first symptoms of a muscular disorder appeared approximately 15 years ago, when he was in his late twenties. The first thing he noticed was that he could not let go of objects. he Later also noticed muscular weakness. The disease affects his job as a butcher, for he has trouble with activities that demand manual dexterity. For a while it has also been difficult for him to walk, especially upon awaking in the mornings. As he ages, he notices that he has very little energy. He has difficulty swallowing and needs fluids help him swallow his food. He also has trouble chewing, and his speech has begun to slur. He has not experienced constipation or diarrhoea. Mr Taylor is married and has two children, aged 17 and 19, who up to now have not experienced muscular weakness. Yet his 17-year-old daughter is often tired and in the last year experienced difficulty in physical education classes. Further questioning revealed that Mr Taylor 's 70-year-old father has a drooping eyelid and a somewhat throaty speechExplanation / Answer
1. Early onset of Mr. Jimenez's daughter is a phenomeon known as anticipation.
2. There are two main types of Myotonic dystrophy DM1 (mutation in DMPK gene) and DM2 (mutation in CNBP gene) Myotonic dystrophy is characterised by was wasting of muscle, cataract, heart conduction defects, endocrine defects and myotonia. DM2 is milder and rarer in severity compared to DM1. Besides DM1 has severe congenital form(absent in DM2) and mild childhood and adult onset form. DM1 is due to CTG repeats while DM2 is due to CCTG repeats. Both types are associated with insulin resistance.
3. Molecular basis of Muscular dystrophy: Myotonic dystrophy is an autosomal dominant disorder with trinucleotide repeat expansion of CTG( in DMPK gene) and CCTG(in CNBP gene) in DM1 and DM2 respectively. DMPK gene codes for myosin kinase whose exact function is not known but probably it is involved in communication and structural integrity. It is known to inhibit a muscle phosphatase which is required for muscle contraction and relaxation.CNBP is a CHC-type zinc finger nucleic acid binding protein. Function of this protein is not known but perhaps it is involved in the production and use of cholestrol . It binds to mRNA with the help of its zinc finger motifs.
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