The relationship of phenotype to genotype in a clinically and genetically well defined population of 157 affected patients and 62 kindreds with facioscapulohumeral muscular dystrophy (FSHD) was examined at the University of Rochester School of Medicine, NY, and Ohio State University, Columbus, OH. Using isometric myometry scores to quantify disease severity, a significant correlation between disease severity and the size of the 4q35-associated deletion was evident, and the offspring were more severely affected than their parents. This generation effect and presence of anticipation in FSHD suggests a possible underlying dynamic mutation and an unstable repeat element within the region of the 4q35 deletion. 
COMMENT. These findings have important significance in the genetic counselling of patients with FSHD. No differences in severity of disease were noted between paternally and maternally inherited FSHD, but a reduction in reproductive fitness in male compared to female patients was an unexpected finding.
FSHD with chromosome 9p deletion is reported in a 31-year-old man who also had congenital anomalies and mental retardation studied at Oita Medical University, Hasama-machi Oita 879-55, Japan . A translocation between chromosome 4q and 9p was not detected. The FSHD in this patient was probably not attributable to the 9p deletion syndrome, which consists of the following: mental retardation, trigonocephaly, high-arched eyebrows, micrognathia, wide-spaced nipples, kyphosis, and inguinal hernias.