Composite heterozygousADTB3Amutation in 2 novel HPS2 patients. (A) Mutational analysis of ADTB3A in 2 patients (Pt 1 and Pt 2) and their parents showed 2 novel mutations. The mother and both the children (Pt 1, Pt 2) present a deletion/insertion in exon 10 at position 1063-1064 of the coding region. C and A are substituted by a 10-base sequence: TATCAATATC. The frame shift in the coding sequence (from the Q at 355 position) leads to a stop codon at position 360 (Q355fsX360). The father and the 2 patients carry a single A insertion at position 1789-1790 in the exon 16, leading to a frame shift (from I at 597 position) and to a stop codon at amino acidic residue 608 (I597fsX608). (B) Cell lysates from both HPS2 Pt 1 and Pt 2 (lanes 3 and 4), a previously identified HPS2 patient¹  (lane 2), and a control subject (lane 1) were separated by SDS-PAGE and probed for the AP-3 subunits (see “Patients, materials, and methods”). Lysates contained 2 × 10⁷ cells per milliliter. β-actin was used to compare protein levels. (C) Western blot probed with anti-β3A using lysates from control (lane 1), the previously identified HPS2 patient¹  using lysates with 4 × 10⁷ (lane 2) and 8 × 10⁷ (lane 3) cells per milliliter, and 4 × 10⁷ from HPS2 patients Pt 1 (lane 4) and Pt 2 (lane 5). β-actin was used to compare protein levels.