Back to Annual Meeting Program

BACKGROUND:Macrodactyly is a rare family of congenital disorders characterized by the diffuse enlargement of 1 or more digits. Multiple tissue types within the affected digits are involved, but skeletal patterning and gross morphological features are preserved. Not all tissues are equally involved and there is marked heterogeneity with respect to clinical phenotype. The molecular mechanisms responsible for these growth disturbances offer unique insight into normal limb growth and development, in general. To date, no genes or loci have been implicated in the development of macrodactyly.
METHODS: In this study, we performed transcriptional profiling of macrodactyly tissue. RNA was isolated from 4 macrodactyly adipose tissue samples and hybridized to Affymetrix U133A Plus 2.0 microarrays. Microarray data were analyzed with principal component analysis, hierarchical clustering, and gene enrichment analysis. Significant results were confirmed using quantitative real time polymerase chain reaction and immunohistochemistry.
RESULTS: 7,295 genes are differentially expressed in macrodactyly adipose tissue compared to subcutaneous adipose tissue. In particular, pleiotrophin (PTN) was 127.6-fold (p-value = 0.049) overexpressed across all our macrodactyly samples. At the biological pathway level, gene enrichment analysis found that subcutaneous adipose tissue (SAT) was enriched for classic adipose tissue gene ontology categories such as “regulation of catabolic processes” and “response to insulin stimulus”. In contrast, macrodactyly tissues demonstrated enrichment of vastly different gene ontology categories such as “extracellular space” and “pattern binding”.
CONCLUSIONS:Pleiotrophin is a promising candidate gene for the pathogenesis of macrodactyly because it promotes growth of nearly all the tissues affected by macrodactyly, including nerve, skin, bone, and cartilage. PTN thus represents a promising target for further investigation into the etiology of overgrowth phenotypes.

Top 10 greatest fold-change probesets in macrodactyly

Probeset ID	Gene	Description	p-value	Fold-Change (vs. subcutaneous adipose tissue)
209465_x_at	PTN	pleiotrophin	0	34.44
223475_at	CRISPLD1	cysteine-rich secretory protein LCCL domain containing 1	1.85E-42	21.42
211737_x_at	PTN	pleiotrophin	0	19.86
220504_at	KERA	keratocan	0	18.51
203913_s_at	HPGD	hydroxyprostaglandin dehydrogenase 15-(NAD)	1.40E-45	15.71
216834_at	RGS1	regulator of G-protein signaling 1	2.72E-25	14.19
205430_at	BMP5	bone morphogenetic protein 5	0	13.97
209466_x_at	PTN	pleiotrophin	0	12.97
209189_at	FOS	FBJ murine osteosarcoma viral oncogene homolog	3.03E-15	12.82

Top 10 greatest fold-change probesets in subcutaneous adipose tissue

Probeset ID	Gene	Description	p-value	Fold-Change (vs. Macrodactyly)
214456_x_at	SAA1 /// SAA2	serum amyloid A1 /// serum amyloid A2	4.20E-45	91.68
208607_s_at	SAA1 /// SAA2	serum amyloid A1 /// serum amyloid A2	4.84E-26	72.59
204424_s_at	LMO3	LIM domain only 3 (rhombotin-like 2)	0	17.56
214146_s_at	PPBP	pro-platelet basic protein (chemokine (C-X-C motif) ligand 7)	1.72E-21	16.27
228434_at	BTNL9	butyrophilin-like 9	0	14.31
211699_x_at	HBA1 /// HBA2	hemoglobin, alpha 1 /// hemoglobin, alpha 2	0	14.28
209458_x_at	HBA1 /// HBA2	hemoglobin, alpha 1 /// hemoglobin, alpha 2	0	13.49
204018_x_at	HBA1 /// HBA2	hemoglobin, alpha 1 /// hemoglobin, alpha 2	0	12.66
204105_s_at	NRCAM	neuronal cell adhesion molecule	2.39E-27	12.49

Enriched gene ontology categories in macrodactyly

# of genes	P-adjusted	GO ID	GO Category
6	0.001	GO:0071363	cellular response to growth factor stimulus
6	0.039	GO:0070848	response to growth factor stimulus
10	0.048	GO:0030199	collagen fibril organization
18	0.011	GO:0001501	skeletal system development
19	0	GO:0005578	proteinaceous extracellular matrix
22	0	GO:0031012	extracellular matrix
30	0	GO:0005539	glycosaminoglycan binding
34	0	GO:0001871	pattern binding
34	0	GO:0030247	polysaccharide binding

Enriched gene ontology categories in subcutaneous adipose tissue

# of genes	P-adjusted	GO ID	GO Category
3	0.002	GO:0015671	oxygen transport
12	0.013	GO:0003995	acyl-CoA dehydrogenase activity
17	0	GO:0046320	regulation of fatty acid oxidation
24	0.023	GO:0032869	cellular response to insulin stimulus
36	0.004	GO:0032868	response to insulin stimulus
43	0	GO:0001525	angiogenesis
55	0.013	GO:0051056	regulation of small GTPase mediated signal transduction
60	0.049	GO:0006732	coenzyme metabolic process
87	0.004	GO:0009894	regulation of catabolic process