Inheritance pattern

AH of these techniques are most often, but not exclusively, used in the clinical setting in order to diagnose abnormalities or to evaluate inheritance patterns of polymorphic proteins. Many appHcations of these techniques exist (61—65). 

MS probably has a genetic component there is a 5% risk for family members of MS patients. Monozygotic twins, who share the same genetic material, are at highest risk, with a 25% to 30% concordance rate.4 However, a straightforward inheritance pattern cannot fully explain the etiology of MS, because only a small proportion of patients have a known family member with MS.4... 

There is a polygenic inheritance pattern which may account for disease susceptibility and expression.7 Family... 

Factor Deficient Inheritance Pattern Estimated Incidence Severity of Bleeding... 

It is clear from family studies that apo(a) gene polymorphism is a consequence of the autosomal codominant Mendelian inheritance of multiple alleles operating at a single chromosomal locus (G7, U4, U6). In families where this simple inheritance pattern was not followed, the existence of a null allele has been postulated (U4, U6). A null allele frequency of 6% was estimated for the subjects... 

This section gives you information on inheritance patterns and understanding risk. 

Reduced penetrance and variable expressivity are factors that influence the effects of particular genetic changes. These factors usually affect disorders that have an autosomal dominant pattern of inheritance, although they are occasionally seen in disorders with an autosomal recessive inheritance pattern. 

Single-gene diseases have clear inheritance patterns. 

The inheritance patterns of multifactorial diseases differ from those of single-gene dborders in several important ways. 

Figure 13-1. Definitions of symbols used to evaluate inheritance patterns for pedigree analysis and relationships within kindreds. Generations are assigned Roman numerals and individuals within each generation are indicated by Arabic numerals. The arrow points at the proband, the person in whom the genetic disorder was first diagnosed.

Figure 13-2. Pedigrees illustrating autosomal inheritance patterns. Recessive inheritance is shown in pedigrees A and B. Note that consanguinity in pedigree B reinforces the hypothesis of an autosomal recessive disorder. Dominant inheritance is shown in pedigree C, in which every affected person has an affected parent.

C. Most X-linked diseases show a recessive inheritance pattern (Figure 13-3). 

Figure 13-3. Pedigrees illustrating X-linked recessive (A) and dominant (B) inheritance patterns. Note the absence of male-to-male transmission in both pedigrees and the predominance of affected males over females in the X-linked recessive pedigree.

F. Mitochondrial disorders exhibit a maternal inheritance pattern. 

Figure 13-4. Pedigrees illustrating inheritance of (A) a mitochondrial disorder and (B) an autosomal dominant disorder exhibiting anticipation. In pedigree A note the similarity to the X-linked dominant inheritance pattern (Figure 13-3A), but incomplete penetrance as exemplified by individuals 11-4 and 111-4. In pedigree B, the age of onset, indicated next to the symbols for affected individuals, becomes progressively earlier with each generation.

The answer is B. The clinical symptoms in this case strongly suggest a mitochondrial disorder affecting both neurologic and musculoskeletal functions. In such cases, no male-to-male transmission is possible because the mother s ovum provides all the cytoplasmic components, including the mitochondria, for the fertilized egg. A pedigree for this family would resemble the inheritance pattern of an X-linked disorder with the likelihood of variable expression. 

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