Extensive laboratory studies showed lymphopenia, low-normal vitamin B12, vitamin D insufficiency, mild hyperhomocysteinemia, and mildly reduced IgA with normal IgG; tTG-IgA and tTG-IgG were negative; FSH and ceruloplasmin were within normal limits; HLA-B27 was not detected on microarray; rheumatoid factor, anti-GAD antibodies, and ANA-1 were negative; screening for HIV, Mycobacterium tuberculosis, Borrelia, and fecal calprotectin were negative. Here, GAD1 is linked to vitamin D deficiency.