The Choroideremia Research Foundation (CRF) is dedicated to supporting research for choroideremia (CHM), a rare inherited disorder that causes progressive vision loss, and aims to find a cure or treatment for affected individuals.

Chromosome 18 Support and Resources is dedicated to supporting families affected by Chromosome 18 conditions through education, research, and community building.

Chromosome Disorder Outreach, Inc is a non-profit organization that supports individuals and families affected by rare chromosome and gene disorders through education, advocacy, and information.

The CRMO Foundation supports patients with Chronic Recurrent Multifocal Osteomyelitis (CRMO) by promoting research, providing education, and fostering community connections.

The CSS Association advocates for individuals affected by Churg-Strauss Syndrome (Eosinophilic Granulomatosis with Polyangiitis) by providing resources, support, and raising awareness about the disease.

Citrin Foundation is a non-profit organization focused on tackling citrin deficiency, a genetic metabolic disorder, by funding research and providing support to affected patients and their families.

The Clear Cell Sarcoma Foundation is dedicated to making clear cell sarcoma survivable through education and research, while providing support for patients and caregivers affected by this ultra-rare cancer.

The Cleft Lip & Palate Association supports, connects, and empowers individuals affected by cleft lip and palate in the United Kingdom, providing information, resources, and community support.

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.

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

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.

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 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.

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

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.

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.