Preferred Minimum: 8 mL whole blood Absolute Minimum: 4 mL whole blood

DFNB4 and Pendred syndrome DFNB4 Baldwin and colleagues reported linkage of a family with recessive, nonsyndromic deafness to chromosome 7q31 in 1995 and designated this locus as DFNB4. Mutations in SLC26A4 are causally related to deafness at this locus. Inner ear computed tomography has shown that DFNB4 includes dilation of the endolymphatic duct (DVA, also called enlarged vestibular aqueduct syndrome, EVA). Pendred Syndrome Pendred syndrome is a common syndromic form of hearing loss (Fraser 1965). Clinical features include inner ear abnormalities, sensorineural hearing loss and diffuse thyroid enlargement or goiter. Inner ear computed tomography has shown that the Pendred Syndrome phenotype includes dilation of the endolymphatic duct and sac, enlargement of the vestibular aqueduct and cochlear dysplasia. This constellation of anomalies is known as Mondini malformation or Mondini dysplasia. SLC26A4 (encoding Pendrin) Mutations in SLC26A4 cause Pendred Syndrome. The gene is a member of the solute carrier gene family and functions as an anion carrier. It has 21 exons and the encoded protein, called Pendrin, has 780 amino acids. Sensitivity is greater than 99%.