Some hypotheses as to the cause of the disease include genetics, cycad seeds, and ingested beta-Methylamino-L-alanine (BMAA) from the consumption of fruit bats. Genetic hypothesis Genetics was first hypothesized due to the situation on Guam.<unk><unk>  was found in great numbers among members of the Chamorro community, so genetic factors were possible. The disease was shown to be familial but not genetic. Chamorro who grew up outside of Guam had not developed the disease, and some non-Chamorro who moved to the island and followed the culture did develop it. Targeted high-throughput sequencing in a relatively small sample demonstrates that disease in many patients can be explained by pathogenic mutations in known genes for neurodegeneration. This includes parkinsonism-dementia due to PINK1 homozygous mutations, a DCTN1 mutation that may be causal for Perry syndrome, Huntington’s disease due to HTT CAG expansions, and FUS and ALS2 mutations. Cycad hypothesis The starch from indigenous Cycas micronesica seeds is consumed in the traditional Chamorro diet. The seeds are ground to make a flour called fadang, and the flour is then used to make flatbread and dumplings. The flour is soaked and washed several times as the seed in its natural form is extremely toxic. Ample research on the cycad hypothesis found a component of the seeds, cycasin, was a potent toxin; it was discovered in the 1950s. As toxic as it was, it would not be the cause of the symptoms of<unk><unk> . Not only that, after nearly two decades of NIH-funded research, animal models failed to reproduce the chronic<unk><unk>  and the hypothesis was rejected for the first time. In 1967, following studies that linked lathyrism to ODAP, Marjorie Whiting, a nutritional antrophologist asked Arthur Bell, a plant biochemist, to test cycad seeds. Arthur Bell and his colleagues discovered another toxic substance in the seeds, BMAA (beta-Methylamino-L-alanine). Initial laboratory results found low levels of free BMAA in cycad flour. The cycad hypothesis was abandoned the second time because the acute toxicity showed by Spencer and Nunn was due to BMAA concentrations in orders of magnitude higher. Further laboratory analysis which included protein-bound BMAA found significant levels in fadang, and found also that the levels were higher in fadang made at settlements with a higher incidence of<unk><unk> . The theory was resurrected by Paul Alan Cox and Oliver Sacks after re-examining aspects of the Chamorro diet. Cox and his colleagues found that BMAA is produced by symbiotic cyanobacteria found in the coralloid roots of cycads. Other than that, fruit bats or flying foxes feed on cycad seeds, and were a common food for the Chamorros. The bats bioaccumulate BMAA in their fat, and eating even a few bats would cause a dose of BMAA similar to levels that produced disease symptoms in the earlier animal models. The content of free BMAA in fruit bats was up to 3 mg/g (approximately 30 mM), while that in the broth in which the fruit bats had been cooked was up to 3 mg/250 ml. Cox also observed decline in fruit bat consumption matching the decline in<unk><unk> . Support for the BMAA theory of the Guam disease came from the finding reported in 2016 that chronic dietary exposure of vervet monkeys homozygous for the APOE4 gene (which in humans increases risk of Alzheimer's disease) to the cyanobacterial toxin BMAA produces dense neurofibrillary tangles and sparse amyloid plaques similar to that found in the brains of Chamorro villagers in Guam who died from<unk><unk> .
Lytico-bodig disease
Crigler–Najjar syndrome
Nakajo syndrome
Degos disease
Fazio–Londe disease
Brill–Zinsser disease
Rhizomelic chondrodysplasia punctata
DeSanto-Shinawi syndrome