There is a group of genetic neurologic conditions called neurocutaneous syndromes where skin findings can be the first clue to a broader syndrome. One of the most common is neurofibromatosis type 1 (NF1), which occurs in up to 1 in 3000 individuals. This is a condition where benign tumors grow on nerve tissue, causing skin, bone, and sometimes brain issues.

One of the first signs of NF1 can be "café-au-lait spots", which are typically light to dark-brown flat, discrete, round or oval skin patches. These spots become more common with age, and can be more common in African-Americans, but most of us have 3 or less. If more than 5 café-au-lait spots (>5mm each) are seen, this should be considered NF1 until proven otherwise. Other findings like freckling in the armpits or groin, or firm, rubbery neurofibromas typically show up later, in preadolescence. Many with NF1 only develop a few fibromas, but they can be quite cosmetically significant for some.

Mental retardation is rare with NF1, but attentional and specific learning issues are common in this disorder. While fibromas are benign, there is a somewhat increased risk of malignancy (3-5%), and brain fibromas can be associated with epilepsy. Short stature and large head are common in NF1.

The majority of folks with NF1 have mild disease, and complications are often correctable to some degree. Treatment focusses on surgery for painful or cosmetically significant fibromas, and addressing learning issues through early intervention and school supports.

Here are the diagnostic criteria for NF1 (2 or more are required for the diagnosis), from GeneReviews:

Six or more café au lait macules over 5 mm in greatest diameter in prepubertal individuals and over 15 mm in greatest diameter in postpubertal individuals
Two or more neurofibromas of any type or one plexiform neurofibroma
Freckling in the axillary or inguinal regions
Optic glioma (tumor of the optic pathway)
Two or more Lisch nodules (iris hamartomas)
A distinctive osseous lesion such as sphenoid dysplasia or thinning of long bone cortex with or without pseudarthrosis (related orthopedic issues)
A first-degree relative (parent, sib, or offspring) with NF1 as defined by the above criteria