Blood Based Methods for Assessing Adolescent Depression in a Subject

1 . A method for assessing adolescent depression in a subject, comprising

(a) measuring an amount of one or more fatty acids in a tissue sample from a subject at risk of suffering from adolescent depression;

(b) comparing the amount of the one or more fatty acids to a control; and

(c) determining a probability that the adolescent subject has depression based on the comparison.

2 . The method of claim 1 , wherein the one or more fatty acids are selected from the group consisting of myristic acid, palmitic acid, palmitelaidic acid, palmitoleic acid, stearic acid, elaidic acid, oleic acid, linolelaidic acid, linoleic acid, gamma linolenic acid, cis-11-eicosenoic acid, alpha-linolenic acid, cis-11,14-eicosadienoic acid, cis-8-11-14-eicosatrienoic acid, arachidonic acid, lignoceric acid, eicosapentaenoic acid (EPA), nervonic acid, docosatetraenoic acid, n-6 docosapentaenoic acid, n-3 docosapentaenoic acid, and docosahexaenoic acid (DHA).

3 . The method of claim 1 , wherein the one or more fatty acids are selected from the group consisting of linolelaidic acid, palmitelaidic acid, alpha-linolenic acid, myristic acid, gamma-linolenic acid, docosatetraenoic acid, palmitoleic acid, linoleic acid, arachidonic acid, and cis-8-11-14-eicosatrienoic acid.

4 . The method of claim 3 , wherein the method comprises measuring the amount of two or more of the fatty acids.

5 . The method of claim 4 , wherein the method comprises measuring the amount of three or more fatty acids.

6 . The method of claim 1 wherein the tissue sample comprises red blood cells, whole blood, serum, platelets, white blood cells, plasma or plasma phospholipids.

7 . The method of claim 1 wherein measuring an amount of one or more fatty acids comprises measuring a percent total of the individual one or more fatty acids as a percent of total fatty acids from the tissue.

8 . The method of claim 7 , wherein comparing the amount of the one or more fatty acids to a control comprises

(a) multiplying the percent total of the individual one or more fatty acids by a predetermined risk factor coefficient to produce an individual fatty acid score; and

(b) summing the individual fatty acid scores to produce a risk score.

9 . The method of claim 7 , further comprising subjecting the percent total of the individual one or more fatty acids to an analysis selected from the group consisting of generalized models, multivariate analysis, and time-to-event survival analysis, to produce a modified risk score; wherein the modified risk score is used to determine the probability for adolescent depression.

10 . A method for determining the fatty acid composition of a tissue membrane, comprising

(a) methylating fatty acids in the tissue sample to produce fatty acid methyl esters (FAMEs) by treatment with a boron-trifluoride methanol solution;

(b) extracting FAMEs from the tissue sample using a hexane solvent;

(c) separating the FAMEs by gas chromatography in a fused silica capillary column;

(d) determining retention times of the FAMEs in the column by means of a flame ionization detector (FID); and

(e) comparing the retention time to a FAME standard; and

(f) calculating FAME response factors for each FAME in the sample based on a FAME standard.

11 . The method of claim 10 , wherein calculating response factors for each FAME comprises:

(i) identifying an area count for a reference fatty acid with a known percent composition in the FAME standard and calculating a ratio of counts to percent;

(ii) applying the ratio to correct area counts for the fatty acids in the FAME standard; and

(iii) calculating a response factor for each of the fatty acids.