Are there any cases of a person with misophonia for which the condition has been passed on to their child? genetics increase one's risk of PTSD, as well PTSD can be developed through vicarious trauma. 

Misophonia condition appears to have the following in common with PTSD;
Anger , muscle tension, feeling of stress, loss of concentration
in reaction to specific sounds 

If a parent has misophonia does that increase the risk for the child to develop the condition as well? 

Are there any known cases that both parent and child have misophonia ?

I can't find research on whether it has been confirmed if misophonia is a stream of PTSD. Or if it has been confirmed if it is genetic.
Noise sensitivity aggregates in families and the estimate of heritability is 36% (Shepherd et al., 2015).

A popular scientific source states that misophonia is not caused by a traumatic event, but might as well be caused by (seemingly) harmless sounds in the past that become associated with stress responses. Both PTSD and misophonia are classified as classical conditioning, though, so there seem to be parallels there (source: Misophonia Institute), but I don't think they misophonia is a form of PTSD.

Heritability of PTSD is approximately 30% in males, and in females it seems even higher (Sartor et al., 2012). 

References
- Sartor et al., Arch Gen Psychiatry (2012); 69(3): 293–9
- Shepherd et al., Noise Health (2015); 17(76): 165–71