Why are almost all inborn errors of metabolism autosomal recessive? Technically, the only inborn error of metabolism I know that is autosomal dominant is acute intermittent porphyria. Also, the only inborn of metabolism I know that is X-linked recessive is Lesch-Nyhan syndrome.

Most deleterious mutations are partial or complete loss-of-function (LOF) mutations; most of those can be functionally compensated for by the presence of a wild-type (normal) copy on the other chromosome and so are recessive. Genes on the non-pseudoautosomal parts of X or Y are effectively hemizygous in males and thus LOF mutations there will likely be dominant. Such LOF mutations in females may also be dominant, depending on whether mosaic expression (due to X-inactivation) results in the phenotype.