Fig4 haploinsufficiency does not improve the Mtm1-knockout phenotype. (A) Hematoxylin and eosin stain of quadriceps muscle from wild-type (WT; plt+/−) (top), Mtm1-knockout (Mtm1-KO) (SM, middle) and plt+/−/Mtm1-KO (DM, bottom) animals. There was no obvious difference in the appearance of the muscle or in the number of abnormal fibers (arrows). (B) Distribution of fiber area. Fiber area was measured from WT; plt+/−), single-mutant (SM; Mtm1-KO) and double-mutant (DM; plt+/−/Mtm1-KO) skeletal muscles. Thirty fibers from each animal were measured (n = 4 for SM and DM, n =2 for WT). (C) Terminal body weight (measured in grams). There was significant reduction in the Mtm1-KO body weight compared to WT. There was no improvement in body weight in plt+/−/Mtm1-KO animals. Average values were as follows: 17.8 ± 0.6 g for WT (n = 8), 11.4 ± 0.7 g for Mtm1-KO (n = 9, P < 0.0001 compared to WT) and 10.5 ± 0.9 g for plt+/−/Mtm1-KO (n = 5, P = 0.48 compared to Mtm1-KO). (D) Haploinsufficiency of Fig4 did not provide any survival benefit. Average survival was 32 ± 2 days for Mtm1-KO (n = 9) and 31 ± 3 days for plt+/−/Mtm1-KO (n = 5).