True statement among regarding autosomal dominant disorder:
(Refer: Robbins Pathologic Basis of Disease, 8thedition, pg no: 140-141)
Autosomal dominant inheritance pattern

Successive or multiple generations of family are affected.
One faulty copy of gene (i.e. mutant allele) in any autosomeand one copy of normal allele.
Disease phenotype is seen in all such individuals.
Patients having disease have 50% chance of passing on thedisease to the next generation.
Both males and females are affected equally.
Both males and females can transmit the condition to progeny
There is atleast one instance of male to male transmission.
Disease manifests in heterozygous state, so at least oneparent of an index case is usually affected.
When an affected person marries an unaffected one, every child has one chance in two of having the disease.
Clinical features can be modified by variations in penetranceand expressivity.
Some individuals inherit the mutant gene but are phenotypicallynormal. This is referred to as incomplete penetrance
Penetrance is expressed in mathematical terms. Thus, 50%penetrance indicates that 50% of those who carry the geneexpress the trait.
In practice, penetrance risk is less than 10%.
If a trait is seen in all individuals carrying the mutant gene but isexpressed differently among individuals, the phenomenon iscalled variable expressivity. For example, manifestations ofneurofibromatosis type 1 range from brownish spots on the skinto multiple skin tumors and skeletal deformities.
In many conditions the age at onset is delayed.
Symptoms and signs may not appear until adulthood (as inHuntington disease).
Many autosomal dominant diseases (e.g. achondroplasia) havebeen shown to be associated with increasing paternal age,
Paternal age is an important determinant in new germ cellmutation, causing both autosomal dominant and X-linkedrecessive illnesses.
Types of mutation
Present early in life
Complete penetrance common
New germ cell mutations in old fathers
Only one generation involved