Pectoralis major defect and Poland sequence in second cousins: extension of the Poland sequence spectrum.

We report on a patient with congenital absence of the left pectoralis major muscle, whose second cousin had the full Poland sequence. This suggests that isolated pectoralis major muscle defect should be included in the spectrum of anomalies characterized as the Poland sequence, postulated to result from disruption of blood supply in the embryonic subclavian and vertebral arteries, the site and degree of obstruction determining the sites and severity of the resulting anomalies. Very few cases are familial; in these the family pattern is compatible with an autosomal dominant mutant gene with reduced penetrance or delayed mutation.