CBC- Genetic Risk

Question 1

What are the two types of tests are commonly used for newborn hearing screening?

Answer 1

otoacoustic emissions (OAEs) and auditory brainstem response (ABR)

Question 2

Seventy-five to eighty-five percent of hereditary nonsyndromic deafness is inherited by which mode of inheritance?

Answer 2

autosomal recessive

Of these, 50% are due to DFNB1. DFNB1 is characterized by congenital, nonprogressive mild-to- profound sensorineural hearing impairment. No other associated medical findings are present (see Figure 1). DFNB1 is diagnosed by molecular genetic
testing of the GJB2 gene (which codes for the protein connexin 26) and the GJB6 gene (which encodes the protein connexin 30). DFNB1 related hearing loss has an approximate prevalence in the general population of 14/100,000 (~1/7,000).

Question 3

What are the common mutations of the DFNB1 gene?

Answer 3

The most common mutation, 35delG, is found in over two-thirds of persons with DFNB1, but at least 80 other disease-causing mutations have been identified. The remaining 2% of individuals with DFNB1 have one identifiable GJB2 mutation and a large deletion which includes a portion of GJB6 i.e., they are double heterozygotes.

Question 4

What is the most common type of hearing loss found in neonates?

Answer 4

Sensorineural

-occurs when there is damage to the inner ear (cochlea), or to the nerve pathways from the inner ear to the brain

Question 5

What is the mode of inheritance of Duchenne’s muscular dystrophy?

Answer 5

X-linked recessive

Approximately one-third of affected individuals have a new mutation in the DMD gene and two-thirds of affected individuals have inherited a DMD mutation from their mothers, who are carriers.

Question 6

What is the symptoms of Duchenne’s muscular dystrophy?

Answer 6

progressive muscle weakness and cardiomyopathy, with death by the third decade in affected males

Question 7

What is the the most common cause of congenital, non-hereditary hearing loss?

Answer 7

CMV (cytomegalovirus)