A total of 14 missense mutations (10 mutations in men and 4 in women) were identified in cysteine codons 611, 618, and 620 (exon10) in 11 patients and three first-degree relatives as follows: four C611Y (three with FMTC and one relative), one C618R (FMTC), one C618S (sMTC), one C620G (sMTC), four C620R (one with FMTC and three with sMTC), and three C620F (one with FMTC and two relatives).
The different RET-activating capability of mutations of cysteine 620 or cysteine 634 correlates with the multiple endocrine neoplasia type 2 disease phenotype.