Table 3.

Characterisation of blood smears of Down syndrome and normal control subjects.

Cell Types	Controls n = 20		Phenotypes and Outcome	Down Syndrome n = 20		Phenotypes and Outcome
Blood smear	Young (YC), n = 10 (age 30–40 years)	Old (OC), n = 10 (age 41–65 years)		Young (YDS), n = 10 (age 30–40 years)	Old (ODS), n = 10 (age 41–65 years)	All older DS participants developed Alzheimer’s disease pathology.
Red cells (RBCs)	Normal (Normocytic)(Figure 8A).	Normal, often paler zone in the centre (Figure 8B).	Staining is more intense at the periphery.	RBCs closed and overlapping (Figure 8C).	Mildly microcytic (Figure 8F).	Microcytic and hypochromic blood film was seen in old DS subjects (Figure 8F)
Neutrophils	Normal	Normal	The cytoplasm is pale pink and contain fine violet granules.	Normal	Increased granulation of neutrophils.	The nucleus has 2–4 lobes of coarse chromatin. Occasionally seen multi-segmented.
Eosinophils	Normal	Normal	Two lobes to the nucleus	Normal	Normal	The cytoplasm was filled with large eosinophilic granules
Basophils	Normal	Normal	Similar size to neutrophils with nucleus.	Occasionally seen large purple/black granules (Figure 8G).	Normal	Found in two cases who had hypothyroidism.
Lymphocytes	Normal	Normal	Normal adult count.	Small lymphocytes.	The lymphocytes population is heterogeneous.	The nucleus was an irregular shape.
Monocytes	Normal	Normal	Large cells, the nucleus was often irregular or kidney shape (Figure 8D).	Lymphocytosis developed and atypical mononuclear cells was found (Figure 8F).	Cells have irregular nuclei, often with nucleoli (Figure 8G).	Some of the monocytes were activated T cells. (Figure 8C,F)
Platelets	Normal	Normal	Platelets were round or oval and had an irregular outline (Figure 8D).	Platelet count was very low (Figure 8E)	Platelet count was reduced, and cell fragmentation was visible (Figure 8F).	Low platelet count is common in young DS, who are prone to suffer from acute myeloid leukaemia (AML).
Bone marrow	Not analysed	Not analysed	Not analysed	The proerythroblast was seen, large cells with high nuclear to cytoplasmic ratio (Figure 8J).	Not analysed	Bone marrow (BM) was hypercellular with gross myeloid hyperplasia. The cytoplasm was dense and there was often a perinuclear pale zone (Figure 8K).
Protein	Expression in	blood	smears
Glycophorin	Normal glycophorin-positive cell membrane (8A).	Normal glycophorin-positive cell membrane (Figure 8B).	Glycophorin is a siloglycoprotein of the membrane of a red blood cell.	RBCs were clumped but normal glycophorin expression (Figure 8C).	Glycophorin-positive membranes were clumped (Figure 8I).	Glycophorin protein could bind with ferritin and is involved in iron transport. DS participants suffer from hypoferritinaemia, that could damage RBC membranes.
RUNX1	Normal expression in the RBCs (Figure 8A).	Normal expression.	RUNX1 protein is crucial for processes such as the self-renewal of haematopoietic stem cells.	RUNX1 are expressed in human bone marrow megakaryocytes (Figure 8J).	There was marked dyshaemopoisis and modest increase of blast cells.	RUNX1 are expressed in bone marrow megakaryocytes, and differentiation of the myeloid and lymphoid cell lineages.
Hepcidin	Hepcidin-positive normal mononucleated cells (Figure 8D).	Hepcidin was found in the RBCs and in MNCs (Figure 8B).	Soluble hepcidin was seen in the RBCs and in MNCs (Figure 8B,D).	Hepcidin-positive monocytes, many of them were abnormal appearance (Figure 8E).	Soluble granular hepcidin was visible around the MNC and scattered throughout the smear (Figure 8G).	Hepcidin may be essential for normal development of RBCs and platelets, as well as transporting soluble proteins.
FPN	Normal appearance in RBCs and MNCs.	Normal appearance in RBCs and MNCs.	FPN expression was seen in all cell membranes.	Normal levels of FPN were present in RBC membranes.	Low levels of FPN were present in RBC membranes.	FPN proteins were expressed in the bone marrow blast cells.
TREM2	Normal membrane-bound TREM2 visible in RBCs membrane (Figure 8H).	Similar pattern but less intense was seen in OC.	TREM2 protein involved in erythrophagocytosis [29].	One young DS (DS18) carrying R47H mutation showed abnormally shaped RBCs (Figure 8I).	Another DS participant (DS55), carrying R47H mutation showed, and accumulation of soluble TREM2 around the MNCs.	TREM2 mutation impaired trafficking of TREM2 to the plasma membrane of erythrocytes in DS, which could affect amyloid clearance from blood cells [29].
Aβ42	Normal	Normal	Aβ42 accumulation was not seen in normal blood smears.	Aβ42 was visible in fractured platelets (Figure 8G).	Aβ42 was visible in in abnormal shape RBCs and co-localised in platelets (very low platelet count) (Figure 8F).	RBCs and platelets participate in amyloid clearance.
CD42b	Normal platelets (Figure 8D)	Normal platelets	CD42b is a platelet marker	Platelet count was very low (Figure 8E).	Platelet count was reduced, and cell fragmentation was visible (Figure 8F)	Low platelet count is also seen in acute myeloblastic leukaemia, which was seen in one young DS.