Fatalities have been rare.In April 2020, a small group of children with evidence of SARS-CoV-2 infection or exposure to COVID-19 were found to display clinical features corresponding to the diagnostic criteria of Kawasaki disease, sometimes accompanied by shock. Kawasaki disease is a rare syndrome which mainly affects young children (adult onset has occasionally been reported). It is a form of vasculitis, where blood vessels become inflamed throughout the body, and it results in a persistent fever. Recovery typically occurs spontaneously, though some children later develop mid-sized or giant coronary artery aneurysms in the heart – a potentially fatal complication. Symptoms of toxic shock (a syndrome caused by bacterial toxins) occasionally occur – an association sometimes referred to as Kawasaki shock syndrome, which is characterized by systolic hypotension or signs of poor perfusion. While the exact cause of Kawasaki disease is unknown, one plausible explanation is that it may stem from an infection triggering an autoimmune and/or autoinflammatory response in children who are genetically predisposed. No specific diagnostic test exists for Kawasaki disease, and its recognition is based on various combinations of clinical and laboratory findings (including persistent fever, widespread rashes, enlarged lymph nodes, conjunctivitis, changes to the mucous membranes, and swollen hands and feet). Characteristics
MIS-C / PIMS-TS is a systemic disorder involving persistent fever, extreme inflammation (hyperinflammation), and organ dysfunction, which is temporally associated with exposure to COVID-19. Onset may be delayed or contemporary with ongoing SARS-CoV-2 infection, which may pass without symptoms.
Buschke–Ollendorff syndrome (BOS) is a rare genetic disorder associated with LEMD3. It is believed to be inherited in an autosomal dominant manner. It is named for Abraham Buschke and Helene Ollendorff Curth, who described it in a 45-year-old woman. Its frequency is almost 1 case per every 20,000 people, and it is equally found in both males and females. Signs and symptoms
The signs and symptoms of this condition are consistent with the following (possible complications include aortic stenosis and hearing loss):

Osteopoikilosis
Bone pain
Connective tissue nevi
Metaphysis abnormality

Pathogenesis
Buschke–Ollendorff syndrome is caused by one important factor: mutations in the LEMD3 gene (12q14), located on chromosome 12.Among the important aspects of Buschke–Ollendorff syndrome condition, genetically speaking are:

LEMD3 (protein) referred also as MAN1, is an important protein in inner nuclear membrane. LEMD3 gene gives instructions for producing protein that controls signaling for transforming growth factor-beta. LEMD3 gene helps in the bone morphogenic protein pathway
Both of the above pathways help grow new bone cells
BMP and TGF-β pathways controls SMADs proteins, which then bind to DNA
LEMD3 once mutated, causes a reduction of the protein, which in turn causes excess of the above two pathways. Diagnosis
The diagnosis of this condition can be ascertained via several techniques one such method is genetic testing, as well as:
X-ray
Ultrasound
Histological test

Differential diagnosis
The differential diagnosis for an individual believed to have Buschke–Ollendorff syndrome is the following:
Melorheostosis
Sclerotic bone metastases. Treatment
In terms of the treatment of Buschke–Ollendorff syndrome, should the complication of aortic stenosis occur then surgery may be required.Treatment for hearing loss may also require surgical intervention.