There is disclosed a method for diagnosing neurotransmission or developmental disorders in a mammal comprising the step of detecting in a bodily fluid of said mammal autoantibodies to an epitope of the muscle specific tyrosine kinase (MuSK). One such method comprises a) contacting said bodily fluid with said MuSK or an antigenic determinant thereof; and b) detecting any antibody-antigen complexes formed between said receptor tyrosine kinase or an antigenic fragment thereof and antibodies present in said bodily fluid, wherein the presence of said complexes is indicative of said mammal suffering from said neurotransmission or developmental disorders. Also disclosed are kits for use in the diagnosis of neurotransmission and subsequent developmental disorders.