শনিবার, ২৩ এপ্রিল, ২০১৬

MUTATIONS


MUTATIONS

As is well known, the term mutation refers to permanent changes in the DNA. Those that affect germ cells are transmitted to the progeny and may give rise to inherited diseases. Mutations in somatic cells are not transmitted to the progeny but are important in the causation of cancers and some congenital malformations.


Details of specific mutations and their effects are discussed along with the relevant disorders throughout this text. Here we cite only some common examples of gene mutations and their effects.
Point mutations result from the substitution of a single nucleotide base by a different base, resulting in the replacement of one amino acid by another in the protein product. The mutation giving rise to sickle cell anemia is an excellent example of a point mutation that alters the meaning of the genetic code. Such mutations are sometimes called missense mutations.

In contrast, certain point mutations may change an amino acid codon to a chain termination codon, or stop codon. Such "nonsense" mutations interrupt translation, and the resultant truncated proteins are rapidly degraded.
Frameshift mutations occur when the insertion or deletion of one or two base pairs alters the reading frame of the DNA strand.


Trinucleotide repeat mutations belong to a special category, because these mutations are characterized by amplification of a sequence of 3 nucleotides. Although the specific nucleotide sequence that undergoes amplification differs in various disorders, all affected sequences share the nucleotides guanine (G) and cytosine (C). For example, in fragile X syndrome, prototypical of this category of disorders, there are 200 to 4000 tandem repeats of the sequence CGG within a gene called FMR1. In normal populations, the number of repeats is small, averaging 29. The expansions of the trinucleotide sequences prevent normal expression of the FMR1 gene, thus giving rise to mental retardation. Another distinguishing feature of trinucleotide repeat mutations is that they are dynamic (i.e., the degree of amplification increases during gametogenesis). These features, discussed in greater detail later in this chapter, influence the pattern of inheritance and the phenotypic manifestations of the diseases caused by this class of mutations.

To these well-known categories, it is necessary to add a heterogeneous group of genetic disorders that, like mendelian disorders, involve single genes but do not follow simple mendelian rules of inheritance. These single-gene disorders with nonclassic inheritance include those resulting from triplet repeat mutations, those arising from mutations in mitochondrial DNA, and those in which the transmission is influenced by an epigenetic phenomenon called genomic imprinting.
With this brief review of the nature of mutations, we can turn our attention to the three major categories of genetic disorders: (1) those related to mutant genes of large effect, (2) diseases with multifactorial (polygenic) inheritance, and (3) those arising from chromosomal aberrations. The first category, sometimes referred to as mendelian disorders, includes many uncommon conditions, such as the storage diseases and inborn errors of metabolism, all resulting from single-gene mutations of large effect. Most of these conditions are hereditary and familial. The second category includes some of the most common disorders of humans, such as hypertension and diabetes mellitus. Multifactorial, or polygenic, inheritance implies that both genetic and environmental influences condition the expression of a phenotypic characteristic or disease. The third category includes disorders that are the consequence of numeric or structural abnormalities in the chromosomes.

বুধবার, ২০ এপ্রিল, ২০১৬

Dizziness


Vestibular Exercise Program to Overcome
Dizziness

                                                                      Aims of Exercise:

1.       To loosen up the muscles of the neck and shoulders, to overcome the protective muscular spasm and tendency to move “in one piece.”
2.       To train movement of the eyes, independent of the head.
3.       To practice balancing in the everyday situations with special attention to developing the use of the eyes and muscle senses.
4.       To practice head movements that cause dizziness, anad thus gradually overcome the disability.
5.       To become accustomed to moving about naturally in daylight and in the dark.
6.       To encourage the restoration of self-confidence and easy spontaneous movement.


All exercises are started in exaggerated slow time and gradually progress to more rapid time.  The rate of progression from the bed-to-sitting to standing exercises depends upon the dizziness in each individual case.  Perform these exercises twice daily.


SITTING POSITION – WITHOUT ARM RESTS

1.       Eye Exercises – at first slow, then quick, 20 times
a.       Up and Down
b.      Side to Side
c.       Repeat A and B; focusing on finger at arms length.

2.       Head exercises – look at a fixed object and move head left and right, up and down.
a.       Head movements at first slow - 20 times
b.      Then quick – 20 times

3.       Shrug shoulders and rotate head, left to right – 20 times
4.       Bend forward and pick up objects from the ground – 20 times
5.       Rotate both head and shoulders slowly, then quickly – 20 times
6.       Rotate head, shoulders, and trunk with eyes open, then closed – 20 times


       STANDING POSITION

7.       Repeat #1
8.       Repeat #2
9.       Repeat #5
10.   Change from a sitting position to a standing position with eyes open, then eyes closed.*
11.   Throw a ball from hand to hand above eye level.
12.   Throw a ball from hand to hand below knee level.
13.   Change from a sitting position to a standing position and turn around in between.
14.   Repeat #6


                                    WALKING

15.   Walk across the room with eyes open, then eyes closed, - 10 times.*
16.   Walk up and down a slope with eyes open, then eyes closed, - 10 times.
17.   Do any games involving stooping, or stretching and aiming, such as bowling, shuffleboard, etc.
18.   Stand on one foot with eyes open, then closed.* 

19.   Walk with one foot in front of the other with eyes open, then eyes closed.*