>80% during meiosis I
>95% derived from maternal meiosis
5% have a translocation with another acrocentric chromosome (Note: translocation errors are not related to maternal age

Ocular findings in Down syndrome

Summary Table: Genotypes and disease associations

Disease associations
HLA-B7 and DR2	Presumed ocular histoplasmosis syndrome (POHS) and multiple sclerosis
HLA-DR3	Thyroid eye disease (also HLA-B8 and genes for CTLA-4)Thygeson’s{' '} superficial punctate keratopathy
HLA-B8	Sjogren’s syndrome
Myasthenia gravis
Type 1 diabetes
Grave’s disease
Sarcoidosis
Intermediate uveitis
HLA-B27	Ankylosing spondylitis
Psoriatic arthritis
Reiter syndrome
Idiopathic, non-granulomatous iritis
IBD
HLA-B25	Acute anterior uveitis
HLA-B44	Retinal vasculitis
HLA-B51	Behcet syndrome
HLA-B54	Posner-Schlossman
HLA-DR4	Sympathetic ophthalmia
Vogt-Koyanagi-Harada syndrome (and HLA-DR1)
Juvenile rheumatoid arthritis
HLA-A29	Birdshot chorioretinopathy (most consistent association of any disorder)
HLA-DR15	Intermediate uveitis
Multiple sclerosis
NB: HLAs A, B and C are type 1 MHC molecules (meaning present on all cells except erythrocytes). HLA-D is the type 2 MHC which is present on APCs mainly