BRAIN LIPIDS OF MICE HOMOZYGOUS FOR THE GENE‘DILUTE LETHAL’(d 1 )

— The lipid composition of brains of mice homozygous for the gene‘dilute lethal’and aged 13‐26 days has been determined. This period covers the early stages of myelination up to the time of death. The brains of affected mice contained up to 8 per cent less total lipid than normal. The lipids increasing most rapidly at this age period were most affected; cerebroside, which normally increased six‐fold between the 14th and 24th days of life, was as much as 25 per cent below normal, but there was no significant reduction in non‐myelin lipids. Studies with [l‐ 14 C]acetate suggested that the low levels of lipids reflected decreased rates of synthesis. In contrast to other reports, no myelin breakdown could be detected, either by TLC for cholesterol esters or histologically. The lowest levels of lipids and slowest rates of cerebroside synthesis occurred in the smallest affected mice; we suggest that the abnormalities in brain lipids reflect a reduced growth rate caused by poorer nutrition in the affected mice.