The familial form cannot be excluded, however, without full investigation of other family members, which is not possible here.

Also, symptoms tend to last longer with the familial form, typically about 24 hours although they may remain for as long as 48 hours.

Some familial forms of polycythemia vera are noted, but the mode of inheritance is not clear.

This syndrome is probably a familial form of mitochondrial encephalomyopathy.

The familial form is inherited in an autosomal dominant fashion with variable penetrance.

Rare familial forms have also been recognized, suggesting a genetic component in some cases.

The bulk of cases are sporadic but familial forms with autosomal dominant transmission have also been described.

Medullary thyroid cancer occurs in two forms, sporadic and familial.

In the familial form, the tumor is almost always bilateral.

One particular familial form is associated with sensorineural deafness (Pendred's syndrome).