17q12 microdeletion syndrome, also known as 17q12 deletion syndrome, is a rare chromosomal anomaly caused by the deletion of a small amount of material from a region in the long arm of chromosome 17. It is typified by deletion of the HNF1B gene, resulting in kidney abnormalities and renal cysts and diabetes syndrome. It also has neurocognitive effects, and has been implicated as a genetic factor for autism and schizophrenia. 17q12 microdeletion syndrome is not to be confused with 17q12 microduplication syndrome, caused by the addition of genetic material in the same region from which it is removed in the microdeletion, or 17q21.31 microdeletion syndrome, another name for Koolen–De Vries syndrome. Presentation
17q12 microdeletions have a variable phenotype, ranging from few or no symptoms to severe disability. The condition is thought to be underdiagnosed, and cases with milder phenotypes may not reach clinical attention unless they have an affected child themselves. The most characteristic symptom is renal cysts and diabetes syndrome (RCAD), also known as "type 5 diabetes", which is caused by deletion of the associated HNF1B gene in the region. RCAD is associated with kidney abnormalities and a characteristic form of diabetes that causes atrophy of the pancreas. However, some people with 17q12 microdeletions have normal renal function. RCAD is diagnosed in approximately 40% of people with 17q12 microdeletions, usually prior to age 25, while kidney abnormalities more broadly occur in approximately 85-90%.People with 17q12 microdeletions have a characteristic facial phenotype, albeit a subtle one not usually obvious in daily life.
Subungual exostoses are a type of non-cancerous bone tumor of the chondrogenic type, and consists of bone and cartilage. It usually projects from the upper surface of the big toe underlying the nailbed, giving rise to a painful swelling that destroys the nail. Subsequent ulceration and infection may occur.There is an association with trauma and infection. Diagnosis involves medical imaging to exclude other similar conditions, particularly osteochondroma. X-ray appearance may reveal a bony protuberance attached to the top or side surface of a toe bone.Treatment is by surgical excision and is effective.More than half are under the age of 18 years and males are affected equally to females. Combined with bizarre parosteal osteochondromatous proliferation, they comprise <5% of cartilage tumors. Signs and symptoms
They tend to be painful due to the pressure applied to the nail bed and plate. They can involve destruction of the nail bed. These lesions are not true osteochondromas, rather it is a reactive cartilage metaplasia. The reason it occurs on the dorsal aspect is because the periosteum is loose dorsally but very tightly adherent volarly. Diagnosis
Diagnosis involves medical imaging.Differential diagnosis includes mainly bizarre parosteal osteochondromatous proliferation (BPOP), which is more irregular and tends to involve the middle of the finger or toe rather than the end near the nail. They are distinct from subungual osteochondroma. Treatment
Treatment is by surgical excision and is effective. Epidemiology
It tends to occur in children and adolescents. Combined with BPOP, they account for less than 5% of cartilage tumors.