Complex sentence: Hypobetalipoproteinemia is a genetic disorder that can be caused by a mutation in the APOB gene, "APOB", although it is usually caused by a mutation in the MTP gene, "MTP".
Split into simpler sentences: Hypobetalipoproteinemia is a genetic disorder that can be caused by a mutation in the APOB gene, "APOB". Abetalipoproteinaemia is usually caused by a mutation in the MTP gene, "MTP".