Genetics
LNS is due to mutations in the HPRT1 gene, so named because it codes for the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT or HGPRT, EC 2.4.2.8). This enzyme is involved in the biochemical pathways the body uses to produce purines, one of the components of DNA and RNA. Defects of this enzyme lead to increased production of uric acid. Since the HPRT gene is located on the X chromosome, LNS is an X-linked inherited disease.The father of an affected male will not be the carrier of the mutant allele, and will not have the disease. An obligate carrier would be a woman who has an affected son and one other affected relative in the maternal line.If a woman is the first in her family with an affected son, Haldanes rule predicts a 2/3 chance that she is a carrier and a 1/3 chance that the son has a new germline mutation.The risk to siblings of an affected individual depends upon the carrier status of the mother herself. A 50% chance is given to any female who is a carrier to transmit the HPRT1 mutation in each pregnancy. Sons who inherit the mutation will be affected while daughters who inherit the mutation are carriers. Therefore, with each pregnancy, a carrier female has a 25% chance of having a male that is affected, a 25% chance of having a female that is a carrier, and a 50% chance of having a normal male or female.Males with LNS do not reproduce due to the characteristics of the disease.
Sinus pericranii (SP) is a rare disorder characterized by a congenital (or occasionally, acquired) epicranial venous malformation of the scalp. Sinus pericranii is an abnormal communication between the intracranial and extracranial venous drainage pathways. Treatment of this condition has mainly been recommended for aesthetic reasons and prevention of bleeding. Signs and symptoms
Sinus pericranii typically present as soft palpable masses along midline skull, which may fluctuate in size depending on body positioning. Classically, these lesions are not associated with color change of the overlying skin,  such as with other vascular lesions such as hemangioma. Cause
The nature of this malformation remains unclear. Congenital, spontaneous, and acquired origins are accepted. The hypothesis of a spontaneous origin in the current case of SP is supported by no evidence of associated anomalies, such as cerebral aneurysmal venous malformations, systemic angiomas, venous angioma dural malformation, internal cerebral vein aneurysm, and cavernous hemangiomas. Mechanism
Sinus pericranii is a venous anomaly where a communication between the intracranial dural sinuses and dilated epicranial venous structures exists. That venous anomaly is a collection of nonmuscular venous blood vessels adhering tightly to the outer surface of the skull and directly communicating with intracranial venous sinuses through diploic veins. The venous collections receive blood from and drain into the intracranial venous sinuses. The varicosities are intimately associated with the periosteum, are distensible, and vary in size when changes in intracranial pressure occur. Diagnosis
Treatment
The surgical treatment involves the resection of the extracranial venous package and ligation of the emissary communicating vein.