VAPs (VAMP (Vesicle-associated membrane protein) associated proteins) are a small gene family that are characterized by the presence of a N-terminal MSP (major sperm protein) domain. MSP domains are molecular complexes with identically linked molecules that form polymers to make polar filaments that round around on another to form macromolecular fibre complexes. Within VAP there are mutations in humans that cause disruptions in cell activity. Of the mutations, the P56S mutation in VAPB (the B isoform of VAP) has been linked to late-onset ALS8 (amyotrophic lateral sclerosis). With its expression, there is formation of large ER (endoplasmic reticulum) aggregates. ER aggregates are misfolded proteins that are clumped together which often lead to the onset of many diseases. Looking at the over-expression of VAPA (the wild-type A isoform of VAP), inhibition of ER-to-Golgi transportation occurred. Decreased segregation of membrane proteins into ER vesicles allowed for the blockage. With obstruction of ER-to-Golgi transportation, VAPA also inhibits lateral diffusion, likely due to its link with microtubules. Lateral diffusion is the horizontal movement of membrane proteins in which they exchange places with neighboring proteins. In order to counteract these disruptions from VAPA, over-expression of FFAT (two phenylalanines in an acidic tract) is necessary. The MSP domain of VAP is known to interact with the FFAT motif, allowing for sterol regulation. Over-expression of FFAT has led to restoration of ER-to-Golgi transport and lateral diffusion of membrane proteins, and also resolution of the large ER aggregates in VAPB-P56S. Expression of FFAT peptides are also restored in ER vesicle budding and disrupted VAP-microtubule association. ER vesicle budding is where there is growth of vesicles from the ER, whereas VAP-microtubule association is the interactions of VAP and microtubules. With VAPA's and VAPB's individual expressions, over-expression of both isoforms in conjunction maintains ER membrane proteins by not allowing lateral diffusion to occur into their transport vesicles. And although this occurs with both being over-expressed, this effect can be dismissed by the expression of the FFAT motif.