Ischiocoxopodopatellar Syndrome with or Without Pulmonary Arterial Hypertension, also known as small patella syndrome, is related to chromosome 17q23.1-q23.2 deletion syndrome and heritable pulmonary arterial hypertension. An important gene associated with Ischiocoxopodopatellar Syndrome with or Without Pulmonary Arterial Hypertension is TBX4 (T-Box Transcription Factor 4), and among its related pathways/superpathways are Signaling by BMP and Heart development. Affiliated tissues include bone and lung, and related phenotypes are aplasia/hypoplasia of the patella and abnormality of the knee