Sabinas brittle hair and mental deficit (SBHMD) syndrome is a rare inherited disease that results in brittle hair and nails and mild intellectual disability. The principal biochemical characteristics of the illness are reduced hair cystine levels, an increased copper:zinc ratio, and the presence of arginosuccinic acid in the blood and urine.
SBHMD syndrome received its name because it was first observed in a small town in Mexico called Sabinas. Some researchers believe that Sabinas syndrome is the same syndrome as Amish brittle hair syndrome and Pollitt syndrome, both of which also feature abnormal development of the hair and nails and mild intellectual disability.
SBHMD syndrome is an inherited genetic disorder, meaning that is passed down among family members. The exact genetic mutation or defect that causes SBHMD syndrome is unknown at this time. The disorder follows an autosomal recessive pattern of inheritance, meaning that two copies of the defective gene must be inherited for the disease to appear.
SBHMD syndrome is extremely rare, with only about 20 known cases. Its actual incidence is unknown. People with the disorder are likely to have parents who are consanguineous, or closely related. Because this condition does not affect any vital organs, it can be assumed that individuals with SBHMD syndrome can function normally, although they may exhibit mild intellectual disabilities.
Sabinas brittle hair and mental deficit (SBHMD) syndrome is a rare inherited disease that results in brittle hair and nails and mild intellectual disability. The principal biochemical features of the illness are reduced hair cystine levels, an increased copper:zinc ratio, and the presence of arginosuccinic acid in the blood and urine.
Cognitive: A common symptom of SBHMD syndrome is a mild intellectual disability.
Eyes: Occasionally, people with SBHMD syndrome will have eye problems, such as changes in the color of the iris, a breakdown of the fibers that form the optic nerve, which could lead to a loss of vision, and changes in the blood vessels of the eye.
Face: People with SBHMD syndrome may have distinctive facial features, including a small or receding chin, small nose, large ears, and an abnormally small head.
Hair: People with SBHMD syndrome tend to have sparse and brittle scalp hair or, in some cases, no scalp hair. Eyebrows, eyelashes, and hair on other parts of the body may also be sparse or absent.
Nails: The fingernails and toenails tend to be poorly developed, thick, and grooved.
Skin: People with SBHMD syndrome may have a skin condition called ichthyosis. This condition is sometimes referred to as fish-skin disease, because the skin develops the appearance of having scales.
Teeth: The teeth may be poorly developed or abnormally positioned and are usually crowded.
Other: People with SBHMD syndrome may also be of short stature and have reduced fertility.
General: Sabinas brittle hair and mental deficit (SBHMD) syndrome may be suspected based on the distinctive qualities of the hair, face, teeth, and skin, in particular, brittle hair and nails. Individuals with SBHMD syndrome may also display mild intellectual disability. Nevertheless, a thorough family history and complete physical exam should be completed.
Blood tests: A small sample of blood may be drawn to test the level of arginosuccinic acid, which is increased in the blood and urine of individuals with SBHMD syndrome. Arginosuccinic acid is normally formed as an intermediate agent during urea metabolism in the liver but is not normally present in the urine. Therefore, elevated arginosuccinic acid in the urine may indicate abnormal liver function.
Hair analysis: Unassisted visual inspection of the hair in patients with SBHMD syndrome may reveal a twisted appearance, known as pili torti. Using a microscope, a clinician may find that the hair is abnormally developed, with a decreased cuticle layer on the outside and a collapsed cortex on the inside. Chemical analysis may reveal decreased levels of sulfur and cystine and an increased ratio of copper to zinc.
Urine tests: A urine sample may be taken to test the level of arginosuccinic acid, which is increased in SBHMD syndrome.
Sabinas brittle hair and mental deficit (SBHMD) syndrome is a rare inherited disease that results in brittle hair and nails and mild intellectual disability.
Recurrent infection: Some people with SBHMD syndrome have recurrent infections, particularly in the digestive tract or lungs.
Liver problems: Arginosuccinic acid is elevated in the blood and urine of individuals with SBHMD syndrome. Arginosuccinic acid is normally formed as an intermediate agent during urea metabolism in the liver but is not normally present in the urine. Therefore, elevated arginosuccinic acid in the urine may indicate abnormal liver function.
Loss of vision:
Occasionally people with SBHMD syndrome will have eye problems, such as changes in the color of the iris, a breakdown of the fibers that form the optic nerve, which could lead to a loss of vision, and changes in the blood vessels of the eye.
General: There is no cure for Sabinas brittle hair and mental deficit (SBHMD) syndrome. Instead, treatment aims to reduce symptoms and prevent complications. People with SBHMD syndrome should be regularly seen by an urologist, dermatologist, and various surgeons, depending on individual patient needs.
Dental care: People with SBHMD syndrome should practice good preventive dental care, including brushing their teeth at least twice daily and flossing once daily. They should also see a dentist every six months and avoid cavity-causing foods and beverages. In addition, crowns or composite fillings may be used on small teeth. Partial or full dentures, implants, or dental surgery may be needed for missing teeth.
Drugs: Antibiotics may be used to treat bacterial infections. Over-the-counter and prescription drugs may also be used to treat the skin condition called ichthyosis. Skin softeners such as petroleum or mineral oil and retinoids, which are derivatives of vitamin A, may improve the appearance and texture of skin.
Education: By law, patients with SBHMD syndrome who suffer from intellectual disabilities must have access to education that is tailored to their specific strengths and weaknesses. According to the Individuals with Disabilities Education Act, all children with disabilities must receive free and appropriate education. This law states that staff members of the patient's school must consult with the patient's parents or caregivers to design and write an individualized education plan based on the child's needs. The school faculty should document the child's progress in order to ensure that his or her needs are being met.
Educational programs vary among patients depending on the child's specific learning disabilities. In general, most experts believe that children with disabilities should be educated alongside their nondisabled peers. The idea is that nondisabled students will help the patient learn appropriate behavioral, social, and language skills. Therefore, some SBHMD syndrome patients are educated in mainstream classrooms. Others attend public schools but take special education classes. Still others attend specialized schools that are equipped to teach children with disabilities.
Because Sabinas brittle hair and mental deficit (SBHMD) syndrome is inherited or caused by a spontaneous mutation, there are no known means of preventing it. Genetics tests are currently not available for the defective gene that causes this disorder. However, genetic counselors may be able to help prospective parents who either have or have a family history of SBHMD syndrome understand the risks of passing the disorder on to their children.
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General: Sabinas brittle hair and mental deficit (SBHMD) syndrome is a rare inherited genetic disorder. The genetic mutation or defect that causes SBHMD is not known at this time.
Autosomal recessive: SBHMD syndrome follows an autosomal recessive pattern of inheritance, meaning that an individual must inherit two copies of the defective gene, one from each parent. Individuals who inherit only one copy of the defective gene generally have no symptoms and are called carriers, because they can pass on the disorder to their children.
If one parent is a carrier, then each child will have a 50% chance of inheriting one defective gene and also being a carrier. If both parents are carriers, each child has a 25% chance of inheriting two defective genes, a 50% chance of inheriting only one defective gene, and a 25% chance of inheriting neither defective gene. Therefore, if both parents are carriers, approximately one in four children will have SBHMD syndrome.
Random occurrence: It is unknown whether SBHMD syndrome can occur as the result of a spontaneous genetic mutation with no family history of the disease.
The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.