On the converse, the failure to thrive we have found in mice lacking mucolipins 3 and 1 point to the importance of examining these and other endolysosomal system proteins, as well as the genes encoding them, in patients with intractable, neonatal failure to thrive and diarrhea, one of the most common causes of infant mortality worldwide (http://www.who.int/gho/child_health/mortality/en/index.html). The gene discussed is MCOLN3; the disease is Failure to thrive.