Clusterbusters is an advocacy organization focused on improving the lives of those suffering from cluster headaches by supporting research for better treatments and providing resources for patients.

CMTC Alliance focuses on supporting individuals with vascular anomalies and birthmarks, providing educational resources and organizing events for families and patients.

CMTC-OVM is a global non-profit community dedicated to improving the quality of life for individuals with rare vascular malformations, such as CMTC and Klippel-Trenaunay, and supports scientific research in this field.

The CMT Research Foundation is dedicated to accelerating research and funding for treatments and cures for Charcot-Marie-Tooth disease, which affects millions worldwide.

The Pulmonary Fibrosis Foundation is dedicated to supporting individuals affected by pulmonary fibrosis through research funding, advocacy, and providing resources and educational programs.

Coalition to Cure Calpain 3 supports research for limb-girdle muscular dystrophy, type 2A (LGMD2A/R1) and focuses on funding researchers and facilitating collaboration, rather than providing direct services to patients.

The Coalition to Cure CHD2 is dedicated to supporting individuals affected by CHD2-related disorders through research, community engagement, and raising awareness about the condition.

The Cody Dieruf Foundation supports families affected by Cystic Fibrosis in Montana by raising awareness, providing emotional and financial assistance, and encouraging health management.

The Coffin-Siris Syndrome Foundation supports, connects, and informs the Coffin-Siris Syndrome community while promoting and funding research related to this rare syndrome.

The Consortium for Outcome Measures and Biomarkers for Neurodevelopmental Disorders is a non-profit organization focused on accelerating clinical treatments for rare genetic neurological disorders.

The Compassionate Friends is a non-profit organization that provides support to bereaved families after the death of a child, offering friendship, understanding, and hope through a network of local chapters and online communities.

Compassion & Choices advocates for end-of-life options, including medical aid in dying, and provides resources to improve care for terminally ill patients.

This organization provides information, support, and education for individuals and families affected by Congenital Adrenal Hyperplasia (CAH).

Congenital Hyperinsulinism International is a nonprofit organization dedicated to improving the lives of individuals affected by Congenital Hyperinsulinism (HI) by providing resources, support, and advocating for better treatments and access to care.

Connect My Variant is a nonprofit organization that focuses on building communities for communication about genetic testing and hereditary disease prevention.

Conquer Chiari is a patient advocacy organization focused on raising awareness and providing resources for individuals affected by Chiari Malformation, a serious neurological disorder.

The Consortium of Multiple Sclerosis Centers focuses on advancing care and education for individuals affected by multiple sclerosis through various programs, advocacy, and professional engagement.