Prenatal Diagnosis of Trichothiodystrophy Associated with a Novel ERCC2 Variant: Expanding the Genotype–Phenotype Spectrum— a case report

In the earliest stages of life, long before a baby is born, the body is engaged in a constant, invisible struggle to repair its own blueprint. Every cell contains a complex set of instructions, and as these cells divide and grow, they occasionally make mistakes or suffer damage from the environment. To survive, the body relies on a sophisticated repair crew, a group of molecular machines that scan the genetic code, find errors, and fix them before they can cause harm. When this repair system fails, the consequences can be severe, affecting everything from how a child grows to how their skin and hair develop. One such condition, known as trichothiodystrophy, is a rare genetic disorder where this repair mechanism is broken. The name itself describes the core problem: the hair becomes brittle and sulfur-deficient, breaking easily, while the skin often becomes dry and scaly. Because the damage occurs at such a fundamental level, the condition can also impact the brain, the immune system, and the ability to withstand sunlight. For doctors and families, the challenge has long been identifying this condition before birth, as the usual signs seen on ultrasound scans are often missing, leaving parents and physicians in the dark until the baby is born.

A team of researchers in Greece recently shared a story that sheds new light on this difficult diagnosis, offering a clearer path for the future. They followed the pregnancy of a twenty-nine-year-old woman who was carrying her second child. By the twenty-eighth week, the medical team noticed something troubling: the baby was not growing at the expected rate. In fact, the growth was so restricted that the baby's measurements fell below the first percentile, meaning the child was smaller than almost all other babies at that stage. Standard tests for common chromosomal issues came back normal, and the amniotic fluid, which surrounds the baby, showed no obvious genetic red flags. Yet, the baby's growth continued to lag, and the mother's blood showed unusually high levels of a specific pregnancy hormone. Faced with a mystery that standard tests could not solve, the doctors turned to a more powerful tool called whole exome sequencing. This technique reads the parts of the genetic code that provide instructions for making proteins, allowing scientists to look for tiny spelling errors that might explain the severe growth restriction.

The genetic analysis revealed the answer hidden within the instructions for a specific protein called XPD, which is part of the body's repair crew. The baby had inherited two different errors in the gene that makes this protein, one from the father and one from the mother. The error from the father was a known change that disrupts the repair process. The error from the mother was a deletion of a small section of the genetic code, a change that had never been seen before and was initially considered too uncertain to count. However, when the researchers looked at the baby's condition, the pieces began to fit together. The mother's genetic change removed a specific segment of the protein that is critical for the repair machine to function correctly. Because the baby had both the known error and this new, untested error, the repair system was effectively broken. The researchers concluded that this new genetic change was indeed harmful, reclassifying it from an unknown variant to a likely cause of the disease. This discovery expanded the known list of genetic errors that can lead to this condition, showing that the spectrum of causes is wider than previously thought.

The story of this pregnancy also highlighted a rare visual clue that appeared during the ultrasound. At thirty-two weeks, the doctors noticed that the baby's scalp looked unusually smooth, with no visible hair. While hair is usually visible on ultrasound images at this stage, its absence was a significant hint. After the baby was born by cesarean section at thirty-four weeks, weighing just 1,170 grams, the physical signs confirmed the suspicion. The newborn had a tight, shiny membrane covering the skin, a condition known as a collodion membrane, and the skin was red and peeling. The baby's face showed deep wrinkles on the forehead, and the eyelids were slightly turned outward. Inside the hospital, the medical team provided careful support to keep the baby warm and protect the fragile skin from infection. A few weeks later, when a small sample of hair was examined under a microscope, it revealed the classic sign of this disorder: a pattern of alternating bright and dark bands, often described as a tiger-tail appearance, which confirms the hair is brittle and lacks sulfur.

Despite the best efforts of the medical team, the infant's health continued to decline. The baby developed a temporary shortage of white blood cells, making it difficult to fight off infections, and an eye examination revealed the early stages of cataracts. The placenta, which had nourished the baby, showed extensive damage and signs of poor blood flow, suggesting that the genetic error had affected the development of this vital organ as well. Tragically, the baby passed away at eight months of age due to respiratory failure caused by a severe lung infection. This outcome is consistent with what is known about the condition, which carries a high risk of mortality in early childhood due to the body's inability to manage infections and repair cellular damage. The absence of brain abnormalities on the baby's MRI scan was also notable, as it matched the pattern seen in many other cases where the brain structure remains intact despite the genetic defect.

This case report serves as a crucial reminder of how modern medicine can connect the dots between a baby's growth, a mother's blood work, and a tiny genetic spelling error. By combining the observation of a smooth scalp on an ultrasound with advanced genetic testing, the doctors were able to identify the condition before the baby was born. This early diagnosis allowed the medical team to prepare for the specific needs of the newborn and provided the parents with clear information about the cause of the illness. The discovery of the new genetic variant adds to the growing understanding of trichothiodystrophy, helping to refine the map of what causes the disease. It demonstrates that even when a condition is rare and difficult to spot, a careful look at the details of fetal development, paired with genetic analysis, can reveal the truth. For families facing similar challenges, this work offers a more complete picture of the condition and a better chance for timely care and understanding.