It is impossible to be certain about what caused Daniel Lambert's extreme weight, but it is considered unlikely to have been caused by an endocrine (glandular) or genetic disorder. Other than his weight gain, he showed no symptoms of a thyroid disorder, and none of his many portraits show the moon face of a patient with Cushing's syndrome. Patients with Bardet–Biedl syndrome and Prader–Willi syndrome, genetic syndromes which can lead to obesity in patients, also suffer from learning disabilities and muscular weakness, but all those who knew Lambert agreed that he was highly intelligent, was extremely strong physically, and, except for erysipelas and venous insufficiency (varicose veins) in his legs, did not suffer from any health problems. One contemporary commentator remarked that "Mr. Lambert scarcely knows what it is to be ailing or indisposed". Lambert's only recorded psychological problem was an occasional "depression of the spirits", during his time in London. Although he had an aunt and uncle who were overweight, his parents and surviving siblings remained of normal build throughout their lives.